EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: Therm Mr. on June 11, 2024, 07:46:21 pm
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Since I just signed up I thought I would say hello. So hi, let me introduce my self. I am a semi retired A/C Contractor. When I was younger, BC (Before Children) I was an electronics hobbyist. Then life got in the way for about forty years and here I am.
So now just an old man with too much time on my hands. Thus I decided to get back onto the “bicycle” so to speak, and take on some electronics projects. Currently I am planning to build a professional quality linear power supply. I know I could buy one cheaper but I want the challenge.
I found a hp/Agilent 3610a schematic and parts list (I think on this site). It’s a 8v@3a and 15v@2a dual supply. It also has CC and CV capability. So, lets get to the questions.
1) It uses a darling pair of 2N6036 power transistors. I believe they are now obsolete. Any suggestion of what to use in their place? Also any suggestion for a fan cooled heat sink for them?
2) Also there is a U3 listed I can not reference and I have no specs for. It is a LM336BZ any idea on what it is.
3). The transformer shows 8 wires feeding three different bridge rectifiers how would I sort that all out? One controls high low range to pass trans, one to display power and one reference and bias supply. How can I spec the correct transformer.
4) There also is no schematic for the LED display driver board. How can I find an alternative for that?
5) Do you know of a more modern alternative that you think may be a better power supply project? A schematic, parts list and maybe PCB design would be helpful?
I will attach the schematic file. Thanks in advance for any help or advice offered. I know I may let out some smoke and $$ but an education costs money sometimes. :)
Therm
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For the start I would consider only a signle channel, so just 1 voltage. The others are kind of copies of the same / similar (e.g. reuse the same PCB tye).
The power transistors in the plan look like MOSFETs. AFAIK HP used IRFP150 - todayone would use the slight higher voltage IRFP250 as an alternative, though the new ones are not as suitable as the old ones.
The circuit is made in a way that it could also use Darlington transistors instead (relatively little changes needed).
One could use integrated darlingtons or separate transistors. For the start it helps to keep the voltage / power small. Scaling is later not that difficult.
For the transformer the control part and display only needs relatively little current. For a better estimate it needs a final circuit, especially the display part. The is a chance to use the same supply for the control and display and this way simplify the transformer selection. For of the shelf transformers one may use 2 separate transformers for the main power and the control part.
For the display part there are several options: old style ICL7106 panel meters, modern cheap panel meter modules from China (usually ADC+µC based) and your own ADC+µC version.
Some need a separate transformers. Some could use the control supply.
More modern PSUs use digital control of the set point. This needs a slightly different circuit at the ref. side / voltage adjustment. The old way with an adjustable divider has its draw backs anyway. There are also plans around for some of the cheap Chinese supplies - largely similar principle, but could be simpler parts. It is definitely worth also looking at 1 or 2 of those.
There are 2 design here in the formum base around LM324 and using 1 supply only.It is a little less flexible, but a real possibilty.
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1)
TIP36CTIP147 (https://www.onsemi.com/download/data-sheet/pdf/tip140-d.pdf) (PNP darlington) is a readily available substitute in a TO-247 package instead of the original (https://www.onsemi.com/download/data-sheet/pdf/2n6035-d.pdf) TO-3. It's only the E3612A that uses the MOSFETs so the schematic is a bit misleading with additional, unpopulated, or substituted components based on model. See service manual (https://xdevs.com/doc/HP_Agilent_Keysight/HP%20E3610A,%2011A,%2012A%20Operating%20&%20Service.pdf) page A-6 to A9.
EDIT: according to the service manual the series pass transistors should be 2N6056 (https://www.mouser.com/datasheet/2/68/get_document-1100791.pdf) not "36"; typo? This is an NPN darlington part. As such use the TIP35CTIP142 (https://www.onsemi.com/download/data-sheet/pdf/tip140-d.pdf) instead.
2) Instead of the LM336BZ5.0 (https://www.ti.com/lit/ds/symlink/lm336-5.0.pdf?ts=1718099402144) you can use a common TL431 (https://www.ti.com/lit/ds/symlink/tl431.pdf?ts=1718110449262) with two 10K resistors to make a 5V zener: anode-10K-adjust pin-10K-cathode. I did just this in my E3611A.
3) You could use two transformers; one for the main power source and another for the floating Ref+Bias supply. Then use an isolated DC-DC for the display supply off of the Ref+Bias supply. The Ref+Bias supply transformer can be low power (< 5VA) as it only supports the op amps and display.
4) The display is just two separate ICL7107 ADC + LED driver boards. You can buy generic 0-200mV 3-1/2 digit voltmeters and add appropriate divider resistors. The important bit to remember is that most of them require their power source to be isolated; that is, the negative sense input (to the voltmeter) should not be connected to the negative power supply lead (to the voltmeter).
5) You do not necessarily need to implement exactly what you see. You can strip away some of the circuit and simplify to better understand how it works (https://www.eevblog.com/forum/beginners/power-supply-need-help-deciphering-the-schematic/msg5444687/#msg5444687) (and this one too (https://www.eevblog.com/forum/beginners/need-help-understanding-how-hp-e3610a-can-output-above-5-volts/msg4081597/#msg4081597)). ie. Rewrite the schematic to show its core parts by removing/substituting the components for a specific supply like the E3610A, removing the the CV/CC indicator parts (comparators), display divider resistors and supply parts. You can add them back in later. Important hint: notice the (+S) symbol connects the output +(red) post with the GND of the Ref+Bias supply.
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The TIP35 / TIP36 are normal transistors, not darlingtons. They are still a reasonable choice, but may need an extra transistor to make it a darlington circuit.
Standard power darlingtons are TIP140/145.
Depending on the skill level it makes sense to not just build a 1:1 copy, but only take the principle configuration and configure / trim the circuit yourself. Here it can really help to simulate the circuit to get a good understanding.
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The TIP35 / TIP36 are normal transistors, not darlingtons. They are still a reasonable choice, but may need an extra transistor to make it a darlington circuit.
Standard power darlingtons are TIP140/145.
Yes, of course. I don't know why I wrote that.
Brain probably thought TIP35/36 were darlingtons to TIP31/32.
Corrections were made to my post.
Thank you.
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Thank you both for the replies. Very informative and helpful.
pqass don't be too hard on yourself mistakes just prove your human. :) The Component and tech info you provided will be very helpful.
Kleinstein your advice will too be considered and appreciated. When I was doing this 30-40 years ago the World Wide Web was a baby. Now I am getting help from people all over the world. This is great.
I am trying to stay as true to this design as possible due to my engineering skills being limited. I understand what things do but the why they do it is is where I am most lacking. My craftsmanship is is good and I learn pretty fast. I would consider my skill level Not beginner, not expert but intermediate. I am definitely open to changing the design as long as my end product is a quality device. I have the time to take my time and learn from the experience.
A few more questions if you don't mind.
1) I can have a good design and good craftsmanship but if I have poor quality components I will not have a good device. How do I assure quality components? Which manufacturers do I look to?
2) The attached section of the schematic shows all the components that are deleted in the 3610a. It seems as though the section needs a complete redesign with the TIP147. Is there a reference somewhere I can use to help with that?
3) Also in this section Q1,2 will be the Darlingtons. It shows two components next to them D6,7 that look identical to Q1,2. These are not listed in the parts list and Have me a bit confused. What are they? Edit: I have uploaded a PDF of the schematic in the original post. It is much more clear and D6,7 are actually Q6,7. Still not listed parts, so still confused.
I am told stupid questions are the ones you don't ask.
Thanks again
Therm
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To Therm Mr. some remarks which might help:
2) Also there is a U3 listed I can not reference and I have no specs for. It is a LM336BZ any idea on what it is.
pls .see datasheet (TI.com etc.). It'S a shunt refetce (similar to a zener diode, but better specs).
3). The transformer shows 8 wires feeding three different bridge rectifiers how would I sort that all out? One controls high low range to pass trans, one to display power and one reference and bias supply. How can I spec the correct transformer.
The HP is already a quite clever design with some good engeneering practices used. For your projecte I'd recommend a 2x12V Transfomrer with 4A capabilty for the main power (based on if you go for the specs HP has in.
It is close to the ratings you need, but of course you have to keep in mind: HP has custom wound their transfomrer, which makes sense if you bulid 1000+ power supplies. for a single project, it's econimic to go for the parts RS etc. sell from shelf.
The other windings: well, you have the +/- reference - I'd take a 2x15V 200mA Transformer for my power supply projects for this part.
And you need power for the DVM/DAM displayd - I'd recommend you buy the digitla modules from shelf (available as 200mV and 20V Fullscale models).
And after the buy, get some transformer that powers these seprately - remeber to keep the auxiliary power separted, no common ground.
4) There also is no schematic for the LED display driver board. How can I find an alternative for that?
pls. take a set of 2 DVM moduels as above mentioned.
5) Do you know of a more modern alternative that you think may be a better power supply project? A schematic, parts list and maybe PCB design would be helpful?
Well, honestly spoken: The performance you will get out of the HP36 series is hard to beat (low ripple, low dissipation, low PARD) and still quite impressive.
I would not call it a "beginners project" to bult a clone (I buld lab bench supplies since more than 3 decades on my own) -- but you can learn a lot.
And, you can download the complete HP36 sevice manual for free -- it has a lot description on how to ansd why they build it the way HP build it.
If you like a more indrotion, I recommend the classic:
DC Power Supply Handbook (Agilent Technologies Application Note 90B)
It's stone old, but for the basic it shows and teaches all the does and don't on how to build an use a power supply .
Have fun!
PS: As you might have noticed, I did not give a remark like you oftne see in forum as "building makes no sense, buy is dead cheaper" etc.
Yes, you get these power supplies from Philips, Delta elektonika, Kepco, etc for 50 bucks on the used market/flea market.
But I think that's not at all you intention - build one is not cheap, but can be very intuitive .-)
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The part with Q4 and Q5 and R44/R45 is there to get better balance in the current with MOSFETs. With BJTs one can usually skip that part if the emittter resistors are large enough.
Q4/Q5 may drawn the wrong way around (E and C swapped). With 4 transistors one should have 4 emitter resistors, not just 2 as in the plan.
What looks like D6 D7 should be Q6 Q7, just a poor scan / copy of the plan.
A lab supply looks simple at first. If done right and with all the details it can be quite envolved and a good learning experience. It is a basic feedback amplifier or regulator problem. A point that makes it a bit tricky is that one wants stablitly / fast regulation even with a changing load (system). In control theory terms this is calling for a robust regulator.
It is not only about getting quality parts, but also about the right regulator tuning (frequency compensation in amplifier terms). There are mainly 2 ways such supplies can go wrong:
one is the thermal design with overheating / overloading parts so they will eventually fail. The other is borderline compensation which results in large overshoot or turn on spikes or oscillation with certain loads (especially capacitive).
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Back in the 1970s, I built the ETI 131 power supply, it is so good that I still use it today. I modified it to use a digital Volts/Amps display as the old analogue meter had become prone to sticking.
With a print board design package you could update the board layouts to have a set manufactured in China for very low cost, JLCPCB charge approx $2 + postage for a set of 5 boards!
The original article is on this page in two zip files:
https://www.thebackshed.com/forum/ViewTopic.php?TID=4422 (https://www.thebackshed.com/forum/ViewTopic.php?TID=4422)
SJ
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Back in the 1970s, I built the ETI 131 power supply, it is so good that I still use it today. I modified it to use a digital Volts/Amps display as the old analogue meter had become prone to sticking.
With a print board design package you could update the board layouts to have a set manufactured in China for very low cost, JLCPCB charge approx $2 + postage for a set of 5 boards!
The original article is on this page in two zip files:
https://www.thebackshed.com/forum/ViewTopic.php?TID=4422 (https://www.thebackshed.com/forum/ViewTopic.php?TID=4422)
SJ
That ETI design is similar to what I used for my last bench PSU build, https://www.eevblog.com/forum/beginners/lm324-power-supply-with-variable-voltage-and-current/msg3582664/#msg3582664 (https://www.eevblog.com/forum/beginners/lm324-power-supply-with-variable-voltage-and-current/msg3582664/#msg3582664)
Slightly simpler than Harrison topology with good performance.
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Thank you andrewtaylor. Good info and references, I will look at all of them. Your post pretty well describes my motivations and intents.
Kleinstein, I must have been editing while you were posting. I added a much clearer PDF of the schematic from the manual to the original post. It shows Q6,7 just like you posted. I will pay close attention to those things you mention.
Thanks for the info Solder_Junkie I have a long way to go in design and testing before I am ready for PCB.
Therm
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Therm, back in the 1970s I used a Dalo etch resist pen and ferric chloride to hand draw and home etch PCBs. I have been using heat transfer paper and ferric chloride until recently.
Only in the past few months have I started to have boards made by JLCPCB, the quality is incredible and they are really low cost. My last batch was delivered in under 2 weeks from uploading on a Saturday, the cost was the equivalent of $4.93 for 5 boards, inc postage and tax. Well worth looking into.
SJ
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If you want some other schematics, a few of Circuit Specialist power supply schematics and a TTi psu schematic / service manual type of pdf and the hp e3620a schematic
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A few more questions if you don't mind.
1) I can have a good design and good craftsmanship but if I have poor quality components I will not have a good device. How do I assure quality components? Which manufacturers do I look to?
2) The attached section of the schematic shows all the components that are deleted in the 3610a. It seems as though the section needs a complete redesign with the TIP147. Is there a reference somewhere I can use to help with that?
3) Also in this section Q1,2 will be the Darlingtons. It shows two components next to them D6,7 that look identical to Q1,2. These are not listed in the parts list and Have me a bit confused. What are they? Edit: I have uploaded a PDF of the schematic in the original post. It is much more clear and D6,7 are actually Q6,7. Still not listed parts, so still confused.
See attached refactor of the Series Pass and Driver transistors for an E3610A implementation.
The non-applicable components (those for the E3612A) were removed or replaced with a short if they were in-series. Also, only one series pass transistor + emitter resistor is shown since it's the minimum required. You can add as many as you need depending on the output current desired; needing more current means hotter transistor so double,quadruple-up to keep any one from exceeding its spec.
1) Quality of components:
If obtained from a reliable source any manufacturer equivalent part would do. The design isn't demanding; no high-speed switching requiring low ESR caps, Q1, Q2, CR4,5,8 can have many alternatives, etc. However, there is some nuance in the design (notice the the ferrite bead L1).
Mini rant: HP seems to use odd valued components (non E12 series (https://en.wikipedia.org/wiki/E_series_of_preferred_numbers#Examples)) and precision (< 5%) in the most mundane of places like pullup resistors; no BOM consolidation at all. No wonder even their simplest products are so expensive.
2) Redesign schematic for darlingtons:
The HP schematic is generic for three implementations (E3610,11,12A) but as is, it's hard to see the core within the clutter. Just re-writing it without the clutter helps (see attached).
3) Diodes across MOSFETs (I think you're referring to):
These are the "body" diodes (https://www.powerelectronictips.com/remember-mosfet-body-diode-faq/) inside every MOSFET.
Sometimes the schematics are not accurate (C2 on page A6 vs A9) or intentionally omit. In the context, Q6,7 are the doubling-up of Q1,3 so should be the same parts.
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you have many projects on the web for linear supplies, CV, CC etc ... with simple pass transistors and op amps
why choosing the complicated route ?
You ask for under 50 watts supplies 8v 3a, 15v 2a .... even cheap ones based on lm723 are good ??
and for the displays, you have low cost but good 3 1/2 digit led or lcd panels, 4 1/2 too if you want to get fancy
even kits like this :
https://www.ebay.com/itm/155160183261? (https://www.ebay.com/itm/155160183261?)
https://www.ebay.com/itm/355584454179? (https://www.ebay.com/itm/355584454179?)
i understand you want to get back on a "bicycle" but start at a proper level, mosfets based psu's are somewhat trickier to build. and avoid self oscillations, pcb's designs too etc ...
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It does not have to be expensive. I don't know what the original 3610A cost but I just (re) viewed Dave's old teardown
https://www.eevblog.com/2011/04/22/eevblog-166-hp-agilent-e3610a-lab-power-supply/ (https://www.eevblog.com/2011/04/22/eevblog-166-hp-agilent-e3610a-lab-power-supply/)
and there is nothing special in it, and the posted schematic also confirms this. So I wonder why it's considered "so good".
Also, you may have a suitable transformer or other parts laying around, a box to put it all in maybe?
For myself, I would put a microcontroller in it. (With ADC and DAC). I much rather have encoders instead of the 10 turn pots, and it can also handle the rest of the front panel (Display / buttons). On top of that, an uC makes it easy to add remote control or to link multiple power supplies.
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The HP supplies were good at the time when they came out. it looks like a good thermal design (no overheating) and the trim of the regulation is likely good (so not much overshoot / ringing). Many of the early supplies from cheaper sources (and new ones from China) had there troubles with overheating / overloading parts to cause a high failure rate. Also some have a tendency to ring or even oscillate with a difficult loads. In fairness one must note that the tricky very low ESR electrolytic capacitors are relatively new. It is not that the HP supply is especially good. It is more than many others were so poor.
The LM723 is not making things much easier and cheaper. A version with LM358 and TL431 can get you better current regulation with only slightly more reference noise. The LM723 still needs the right compensation and needs extra complications to work down to 0 V.
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This is a typical schematics of a cheapo 18V/3A PSU (or 15V/3A, etc) you may find under dozens of various names, with LED or LCD 710x based meters (Voltage/Current)..
I got one as a gift and it works fine.. I wanted to mod it heavily, but finally I resigned on that effort and I only added a front panel switch and a resistor with the current shunt R22 split into 3A and 0.2A ranges.
PS: there are 2 additional simple 7809 floating (isolated) power sources inside on the pcb (the transformer has got 2 additional windings + diode bridges + caps + 7809s), powering the two (current and voltage) front panel 7106 LCD meters. They are sensing the current and voltage at the shunt R15.
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It does not have to be expensive. I don't know what the original 3610A cost but I just (re) viewed Dave's old teardown
and there is nothing special in it, and the posted schematic also confirms this. So I wonder why it's considered "so good".
Also, you may have a suitable transformer or other parts laying around, a box to put it all in maybe?
For myself, I would put a microcontroller in it. (With ADC and DAC). I much rather have encoders instead of the 10 turn pots, and it can also handle the rest of the front panel (Display / buttons). On top of that, an uC makes it easy to add remote control or to link multiple power supplies.
HP Catalog for 1993 has it for $300. That's $661 in today's money.
I like the aesthetics and UI simplicity. Although, I wish it had an output on/off.
Sometimes it's good to go back to basics - to build a minimalist implementation in order to fully understand the core.
See here (https://www.eevblog.com/forum/beginners/power-supply-need-help-deciphering-the-schematic/msg5444687/#msg5444687) and attached. You can always add on to it later.
Furthermore,
the attached implementation (below) of the circuit (link above) does work. However, it does have some issues that I'm working through. This is when learning happens.
That is: Understand theory > simulate it > prototype it > test/characterize > revise until all goals are met > product-ize it.
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We have a similar E3630A and it is pretty stable. If i manage to adjust it for 10 V and come back some hours later it will be within 1 mV. It's well built, except the meter push buttons sometimes jump out. Maybe i should use glue to fix them once and forever.
Regards, Dieter
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The HY1803 uses the same basic principle, but it still misses out on details of the compensation that can make the difference between good and prone to oscillation (or awfully slow). The resistors in series to the feedback cap at the OP-amp are the step of going from a crude I-regulator to a better PI regulator. The additional RC element at the voltage divider makes it a full PID.
There is quite some though / calculation (or try and error) in these small details. It is a shame those cheap supplies failed in this detail that adds very little costs, but can make quite some difference in the performance. Especially with modern simulation tools available there is no good excuse for this in a series product.
Adding at least a simple output on / off is relatively easy and you are free to do this for a DIY build.
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This thread is giving me one heck of an education. Thank you all.
That power supply handbook is chock full of info.
Lots of variety in all those schematics posted also.
pqass is the pic I uploaded in this post the proper way to add another trans?
Do you guys have any preferred schematic drawing software? I did that one on one of the online programs. It was a bit clunky. I am fairly good with CAD programs. I use BricsCad because AutoCad only rents now you can't buy it. But Brics still let's you buy.
It will take me a bit time to absorb all the info in this thread. I likely wont be able to absorb it all. But I will get a lot of it. This place is great.
Therm
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pqass is the pic I uploaded in this post the proper way to add another trans?
Do you guys have any preferred schematic drawing software? I did that one on one of the online programs. It was a bit clunky. I am fairly good with CAD programs. I use BricsCad because AutoCad only rents now you can't buy it. But Brics still let's you buy.
See attached for revised schematic. Changes/corrections are in red.
As I'd said, HP loves odd values but you can substitute:
1K for 1.2K, 4.7K for 5K, 1N400x (x=3-7) for CR8, 1N4148 for CR4,5, and
don't bother with L1 for now (it's actually a tiny ferrite donut on the leg of Q2).
Yes that's how to add another transistor.
The emitter resistor is very low value of about 1R or less.
It's used to equally spread the current load across all parallel transistors due to manufacturing differences.
I like kicad. It's actively being developed and provides much more than what I need (schematic capture and layout of simple circuits).
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That power supply handbook is chock full of info.
completely agreed .-)
the detailed description in a HP E36xx service manual gives you even more "brain food"
Lots of variety in all those schematics posted also.
Here is where the pain in brain begins: Question is where to start? Which one to choose/take?
If I would be in your situation, my recommendation: Start with any one, and finish it to the very end. So stay fully focussed. Once your through this very time consuming 1st build, the next ones will be easier.
Next ones? Yes, one rarely stays with only a single power supply when you are into this hobby .-)
Do you guys have any preferred schematic drawing software?
I like KiCad. Fairly easy to learn, a lot of tutorials,
and good for PCB (BTW: v.7 has an autorouter extension, I guess v.8 will soon follow to get one).
It will take me a bit time to absorb all the info in this thread. I likely wont be able to absorb it all. But I will get a lot of it. This place is great.
Take your time, as previously Kleinstein has mentioned: Build is simple, but build it RIGHT to work without oscillation etc. is the key that divides a design from poor to "excellent for use every day".
Go for the last.
my 2cts of opinion .-)
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For relatively simple schematics one can also use the a simulation tool like Tina or LTspice. For getting suitable values for the tuning (e.g. the small capacitors) the simulation tool can be a big help.
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Thanks pqass that is very helpful info. I did download KiCad I am about half way through the drawing. So it is pretty intuitive. I stopped to resolve the below issue before I get ahead of myself and have to backtrack. The one thing I did notice is the library is missing many components. Like the tip142 not being in there. It does not seem like a big deal because I can use others as a generic symbol. Seems like it would only be a problem if I wanted to print the parts list, which I don't plan on doing. But I do like the program so far. I'll post the drawing for any critique when I am done.
At the very end of the drawing there are two caps, c3 and c4 that are deleted in the 3610. Now wiring a direct by-pass looks like it would create a dead short between output positive, output negative and ground. My thoughts are to eliminate the line between ground and output positive but maintain the line between output negative and ground. Am I thinking correctly here?
andrewtaylor thanks for the advice and I am all in on the 3610 build. The other schematics will be good learning tools and references in the future. Also I found an app Electronics Engineer Helper. Lots of good tools to help. I use a Mac so good software is not as prolific as on windows.
Kleinstein I do plan on working a little with both TINA and LTspice to evaluate them for use. One can never have too many tools.
Therm
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Tina and LTspice are about comparable - usually no real need to have both. There is still some learning curve for the UI.
In the original plan one could get away without C4 or or C5. They both get a capacitive link to mains ground, mainly for RFI purposes. Because of RF oddities (even wires can have an effect) it can still make sense to have them both.
A capacitor like C3 at the output is essential and the capacitance (with details like ESR) here is an important point in the design. One may even consider more than 1 capacitor in place of C3, like a small (e.g. 100 nF range) film or ceramic and a larger electrolytic (e.g. 100 µF, possibly more) that acts as capacitor with some ESR. The compensation is a bit similar to classic LDO regulators and similar to these the regulator can be a bit picky about the output capacitor(s).
The plan has different ground symbols and it is correct to have the positive output connected to the +S ground that is also the center of the regulator supply.
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Thanks pqass that is very helpful info. I did download KiCad I am about half way through the drawing. So it is pretty intuitive. I stopped to resolve the below issue before I get ahead of myself and have to backtrack. The one thing I did notice is the library is missing many components. Like the tip142 not being in there. It does not seem like a big deal because I can use others as a generic symbol. Seems like it would only be a problem if I wanted to print the parts list, which I don't plan on doing. But I do like the program so far. I'll post the drawing for any critique when I am done.
At the very end of the drawing there are two caps, c3 and c4 that are deleted in the 3610. Now wiring a direct by-pass looks like it would create a dead short between output positive, output negative and ground. My thoughts are to eliminate the line between ground and output positive but maintain the line between output negative and ground. Am I thinking correctly here?
With Kicad, you typically won't find specific part numbers in the library. So when adding to the schematic editor choose generic symbols like "Q_NPN_Darlington_BCE" for TIP142; making sure the pin numbering 1,2,3 corresponds to your actual part ordering for B,C,E. Then change the value of the highlighted symbol via mouse right button > Edit Value item to "TIP142". After you're done with the schematic editor, run the Footprint Assignment Tool to select the correct footprint for every part. In your case, for TIP142, you can choose "Package_TO_SOT_THT:TO-247-3_Horizontal_TabUp" if you wish to sandwich the part horizontally between heatsink and PCB.
In the case of C5 and C4... don't take my earlier advice too literally ("non-applicable components were removed or replaced with a short"). Context is important. The E3612A has high-voltage outputs (120VDC) and as such will have Y-rated safety caps to earth ground (the pitchfork symbol, aka the 3rd mains prong). So, no, don't short C5 and C4; just remove them entirely. You will find all these lab supplies have the earth ground available on the front face-plate giving the option to the user to tie the positive or negative output post to it, or not; leaving the output "floating" WRT earth (ie galvanically isolated).
Try to understand the purpose of each component.
Is the component required for core functionality or does it support a secondary feature (eg. CV, CC, voltage, current display)?
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Kleinstein I do plan on working a little with both TINA and LTspice to evaluate them for use. One can never have too many tools.
Therm
I use both, LTspice is excellent if you are using their devices, but I find the user interface of Tina "better" for most uses. I guess it depends on what you become used to.
While I have a copy of KiCad, I find it frustrating to use and much prefer Sprint Layout: https://www.electronic-software-shop.com/lng/en/electronic-software/sprint-layout-60.html (https://www.electronic-software-shop.com/lng/en/electronic-software/sprint-layout-60.html) but as with Tina vs LTspice, it depends on your preference. I have made a lot of boards, both home etched and made by JLCPCB, using Sprint Layout.
SJ
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KiCad is quite impressive it has a few quirks but is easy to learn and use and you can't beat the price. The symbols are not scalable so they are probably not vector drawings. You guys really hooked me up good with that one. KiCad is pretty functional for a free program. I expect Ltspice/TINA will be good too.
This is the drawing I did in KiCad. I left everything in for now ie, display power and CC/CV circuits. I wanted to have a good representation of what a 3610a circuit looks like, not a multi unit circuit. Also I used three transformers that just for drawing purposes for now I will figure that out as I go. I found some DVM modules at Mouser made by Murata, that are loop powered by the input voltage and current. They would eliminate the power supply circuit. I need to investigate that a bit more though.
I will admit the whole V- V+ and floating ground vs earth ground thing has me a bit confused. Also +S is a giant WTF. But its only a matter of time before it starts to sink in. Right now the connector J1 has two number threes but it won't be hard to sort out once I pick a display. Let me know if you see anything I messed up.
Thanks again Gents
Therm
Found a few errors in the original file so I deleted and re-uploaded.
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Wow, that diagram is impressive! Well done getting that far in KiCad. The harder part is turning it into a print board layout 😂
SJ
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With Kicad, you typically won't find specific part numbers in the library. So when adding to the schematic editor choose generic symbols like "Q_NPN_Darlington_BCE" for TIP142; making sure the pin numbering 1,2,3 corresponds to your actual part ordering for B,C,E. Then change the value of the highlighted symbol via mouse right button > Edit Value item to "TIP142". After you're done with the schematic editor, run the Footprint Assignment Tool to select the correct footprint for every part. In your case, for TIP142, you can choose "Package_TO_SOT_THT:TO-247-3_Horizontal_TabUp" if you wish to sandwich the part horizontally between heatsink and PCB.
pqass
Try to understand the purpose of each component.
Is the component required for core functionality or does it support a secondary feature (eg. CV, CC, voltage, current display)?
I was finding mistakes the more and more I looked over the circuit drawing. I was trying to make sure everything was right before I tried to run the foot print assignment tool. Just to try it out, not because I have finalized anything. I was editing because there were some lines drawn over the top of the symbol that I did not put there. U4 and U5 which of both have A and B sections and the A and B were doubling and I was trying to figure out why. So I went back and re-read the above several times trying to look for answers. Thats when it hit me and I started to understand what you were saying.
So now I am wondering if I need to go back and change some of the components I inserted not just edit them. I am going to post to pics in this post to see if you can confirm that I do now understand your post.
The pics are of Q 1 and 3. I changed the pins on Q 3 to match the transistor in the other picture. Did I do that correctly?
When I was putting in U2, 4 and 5 I just picked the symbols at random if they matched the numbering I needed for the drawing. If not I edited them to match. The components in the parts list did not have matches in the symbol library. Will that screw me later when I go to the footprint assignment tool? Better to correct it now than later.
Where can I cross reference obsolete parts to find the modern replacements?
Kleinstein good info on the caps thanks.
I just noticed that Q3 changed to Q2. I re-uploaded to fix. I have had this happen on many things while working is it me or the program just glitching?
Thanks
Therm
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The pics are of Q 1 and 3. I changed the pins on Q 3 to match the transistor in the other picture. Did I do that correctly?
Yes. Q1 should look like Q2 in your attachment. That is, for the TIP142 part, pin 1=B, 2=C, 3=E.
If not I edited them to match.
Not sure what you mean. I hope you didn't change the symbol via the Symbol Editor. That shouldn't be necessary for the complexity in this schematic. The haystack is pretty big so sometimes it's hard to find an appropriate generic symbol for your needs.
Where can I cross reference obsolete parts to find the modern replacements?
LF411 and LF442 both have generic footprints; 1 opamp, and 2 opamp packages, respectively. If you implement IC sockets, you can try many specific devices during testing. Unfortunately, there are lots of modern parts to choose from which usually requires you to read the datasheet on the old part and compare it to more common modern parts. I'm not aware of a specific xref list except to say that my 2nd Ed Art of Electronics says LF411=jellybean. Digikey also still sells the LF411, however, the LF442 is listed as obsolete though shows substitutes (not sure of the value, worth checking though).
LM336BZ5.0 can be substituted for with a TL431 + two 10K (https://www.electrothinks.com/2023/07/tl431-shunt-voltage-regulator-circuit-working-explanation.html) divider resistors.
LM393 is still readily available.
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Yes I went into the editor and edited till I got a match. Is there a way to reload that library? :palm:
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You should have seen a message (just under the icons): "Editing symbol ? from schematic. Saving will update the schematic only."
So delete the symbol from your schematic and Add the generic one back in.
The edited symbol might still be in a cache in your local directory so don't re-select it as it may be listed as most recent in the Add list.
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Thank you, That is exactly what I saw. Your help is very much appreciated.
Therm
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I found some DVM modules at Mouser made by Murata, that are loop powered by the input voltage and current. They would eliminate the power supply circuit. I need to investigate that a bit more though.
I will admit the whole V- V+ and floating ground vs earth ground thing has me a bit confused. Also +S is a giant WTF. But its only a matter of time before it starts to sink in. Right now the connector J1 has two number threes but it won't be hard to sort out once I pick a display. Let me know if you see anything I messed up.
The thing with lab power supplies is that you can dial the output down to 0V. So you can't really power the voltmeter with the output voltage as it will cut-out at some point as you dial down. Also, ammeter modules include their own shunt (another low value resistor like R2) which will lower the output by the burden voltage (https://en.wikipedia.org/wiki/Multimeter#Burden_voltage).
In the case of the E3610A R2=0.1ohm, therefore a 1A current will produce 100mV and a reading of 1000 on a 0-200mV full-scale 3-1/2 digit voltmeter.
In the case of the E3611A R2=0.2ohm, therefore a 1A current will produce 200mV but to use the same voltmeter, R11+R12 (10K+10K) divider is used to cut that in half.
So the purpose of the R11+R12 divider is to adapt the shunt to the voltmeter selected (as ammeters are just voltmeters measuring shunts).
Same for R18+R17; to adapt the output voltage range to the voltmeter selected (showing the output voltage reading to the user).
Yes, I saw the pin3 referenced twice mistake too.
Now, onto a critique of your schematic...
Wires should go from symbol pin to symbol pin; don't just end wires as it will fail DRC and will be a mess going forward into the PCB layout stage. Unused pins should have the "x" (no connection) flag attached (see right icon bar).
Don't mimic switches with wires; there are many switch symbols. Search under the "Switch" category in the Add symbol popup or search for "SPST", "DPDT", etc. in the search bar. It's a big haystack. For example, if you can't find one like "SP7T", open "SW_SP3T", edit it, create/save-as to your own library for future projects.
I find HPs schematic hard to follow with all the long wires going between sub-circuits. I like to isolate bite-sized parts (but not go too microscopic) and connect them through global or local labels. See what others have done on the Internet to get a feel for it.
Use the power symbols; Add symbol from the "Power" category or ⏚ on right icon bar. Don't just end wires with "+12V" or "[+S]" text. If you have two rails that are the same voltage but should be isolated, then select a different power symbol (eg. "+5V", "+5VD"). Also, google "kicad PWR_FLAG".
[Not in yours but] most schematic readers expect inputs on the left, outputs on the right. Similarly, positive power is ordered above GND and negative power below GND.
Once you think you're done with the schematic,
a. either manually change all reference designators (eg. "Q?", "U?") to match HPs schematic or use the Annotate Schematic popup to (randomly) assign them for you.
b. Then run rules check via Electrical Rules Checker popup.
c. Then call Assign Footprints popup to select footprints for each symbol.
d. Only then you can proceed to the PCB layout editor.
Attached, you will find my take on a re-written version of the the E3610A. Your style may be different and that's okay.
a. I've purposely cleared all reference designators to "?" and kept the default for the symbol value field to show the generic symbol chosen. I also re-organized and separated the sub-circuits into functional chunks which I believe are easier to read/understand.
b. Op amp GND (▽) and "+S" label are attached at the positive output post.
c. I use the protective earth symbol for the 3rd plug prong which is isolated from op amp GND above. Unfortunately, the stupid plug symbol has a ⏚ which is confusing with PE symbol attached to the pin. I/you should just make your own library version without the ⏚ lineart.
d. +5V in the original isn't really used as a power rail. It's really a stable +5V reference so I made it a label instead of using a power symbol.
e. Notice the display power uses +5VD/GNDD which is isolated from any other rail.
f. I've substituted a TL431+2*10K for the LM336.
g. I've used connectors for J1 and the output posts. As far as I'm aware, you can't split a single connector; distributing the pins over the schematic like HP did for J1. It must be a single n-way connector with wires or labels attached.
That's all for now.
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That is all? That is a mind and a half full. :)
I do already have some questions but let me digest that all a for bit first. While drawing the HP version I learned a lot just from the process. As I wrestled my way through it and KiCad together, I though I might go into info overload. Yet I lived through it. That drawing was a little intense to flow through. By breaking it up into bite size nuggets you definitely have made it little more friendly to the brain for sure. That must have been a bunch of work.
I will probably read that last post 10 times before I comprehend the better part of it. I can't even begin explain how much I appreciate the education. I started a spread sheet for a parts list that I have been working on with this. I have even got a couple of saved carts with parts at some suppliers. I want to get these parts so I can start building some circuits for testing. I just have to be careful not to get ahead of myself.
Getting some build time on the bench with a DMM and a scope will hopefully pull all this random stuff rattling in my head together.
Thanks
Therm
PS Thanks for the critique. It will certainly help me improve my drawings.
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The thing with lab power supplies is that you can dial the output down to 0V. So you can't really power the voltmeter with the output voltage as it will cut-out at some point as you dial down.
Thinking about it that is pretty much a no brainer. You can’t power a display at zero volts. Sometimes I wonder about myself.
Wires should go from symbol pin to symbol pin; don't just end wires as it will fail DRC and will be a mess going forward into the PCB layout stage. Unused pins should have the "x" (no connection) flag attached (see right icon bar).
This is very helpful I have been deleting unused pins or picking the wrong symbol to try and match the HP drawing. It would have become a big problem later. Thanks
Don't mimic switches with wires; there are many switch symbols. Search under the "Switch" category in the Add symbol popup or search for "SPST", "DPDT", etc. in the search bar. It's a big haystack. For example, if you can't find one like "SP7T", open "SW_SP3T", edit it, create/save-as to your own library for future projects.
Noted and I will make the changes. When using a created library do you need to switch back and forth between libraries to use them? Or how does that work?
I find HPs schematic hard to follow with all the long wires going between sub-circuits. I like to isolate bite-sized parts (but not go too microscopic) and connect them through global or local labels. See what others have done on the Internet to get a feel for it.
I find HPs schematic a bit quirky too. I do understand the circuitry much much better the way you drew it. But I lose the big picture in the little bits and need to see the circuit whole and connected to visualize the and understand project. If thats make any sense.
Use the power symbols; Add symbol from the "Power" category or ⏚ on right icon bar. Don't just end wires with "+12V" or "[+S]" text. If you have two rails that are the same voltage but should be isolated, then select a different power symbol (eg. "+5V", "+5VD"). Also, google "kicad PWR_FLAG".
I think I am starting to get this. I am still a bit confused by all the different power rails and grounds and the reasons for them. My understanding of this part of it is getting better all the time. I imagine at some point I will have that epiphany moment.
Once you think you're done with the schematic,
a. either manually change all reference designators (eg. "Q?", "U?") to match HPs schematic or use the Annotate Schematic popup to (randomly) assign them for you.
b. Then run rules check via Electrical Rules Checker popup.
c. Then call Assign Footprints popup to select footprints for each symbol.
d. Only then you can proceed to the PCB layout editor.
I have a ways to go before I get here. I have been putting HPs designators in because it helps me match to their parts list. So are you saying redraw and just leave them blank for now?
Attached, you will find my take on a re-written version of the the E3610A. Your style may be different and that's okay.
a. I've purposely cleared all reference designators to "?" and kept the default for the symbol value field to show the generic symbol chosen. I also re-organized and separated the sub-circuits into functional chunks which I believe are easier to read/understand.
They are much easier to understand. How do the global/local labels work when running the rules and PCB layout? Also where can I find out about using them and where to create them.
b. Op amp GND (▽) and "+S" label are attached at the positive output post.
Noted
c. I use the protective earth symbol for the 3rd plug prong which is isolated from op amp GND above. Unfortunately, the stupid plug symbol has a ⏚ which is confusing with PE symbol attached to the pin. I/you should just make your own library version without the ⏚ lineart.
I wondered why you did that what is the difference between the two?
d. +5V in the original isn't really used as a power rail. It's really a stable +5V reference so I made it a label instead of using a power symbol.
? Reference for what? This has me confused.
e. Notice the display power uses +5VD/GNDD which is isolated from any other rail.
Noted this I understand.
f. I've substituted a TL431+2*10K for the LM336.
In HPs drawing is this a mistake? The LM336 has no adjust wire attached what exactly is this doing?
g. I've used connectors for J1 and the output posts. As far as I'm aware, you can't split a single connector; distributing the pins over the schematic like HP did for J1. It must be a single n-way connector with wires or labels attached.
I liked how you did that. The actual HP device has just such a connector. When I looked it up in the symbol library it did not have the yellow rectangle around it. Thats when I figured out you must have edited and created it. Then I did the same it was a good lesson by itself.
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When using a created library do you need to switch back and forth between libraries to use them? Or how does that work?
No.
You can create a library from the Symbol Editor menu: File > New Library... Save to <home>/Schematic/lib/<library name>
Then in the Schematic Editor, add it to the bottom of menu: Preferences > Manage Symbol Libraries...
It will show up as an expandable category on the Add (symbol) popup. And the content is searchable via search bar.
But I lose the big picture in the little bits and need to see the circuit whole and connected to visualize the and understand project.
I agree, too fine a sub-circuit breakdown leads to disjointed puzzle pieces. That's where placement of the pieces and label names visually helps (flow from left -> right, top -> bottom). You can always create a high-level function diagram in a corner. Or if too elaborate for one large sheet, use hierarchical sheets. BTW: you can change to a larger sheet via File > Page Settings then scale down to a US Letter when printing to PDF.
I am still a bit confused by all the different power rails and grounds and the reasons for them.
The display power is isolated from the rest of the circuit because ICL7107-based 3-1/2 digit voltmeters need that; can't be galvanically attached to the thing they're measuring.
The op-amp power needs to be isolated because the only point of its attachment will be its GND with the +OUTPUT post. Why? A:Because the opamps need to change the voltage on the base of the darlingtons relative to their emitters (which are two low-value resistors away from +OUTPUT) and don't have to take into consideration the variable output voltage setting. Like a bird on wire; it doesn't know it's at many KVs relative to earth.
I have been putting HPs designators in because it helps me match to their parts list. So are you saying redraw and just leave them blank for now?
No. I left them ? because (1) I didn't want to distract from calling them something else (by auto generating) vs. the HP drawing., and (2) it's more work to match HPs drawing. The intent of my drawing is to show sub-circuit breakdown and layout, not do it for you. :)
How do the global/local labels work when running the rules and PCB layout? Also where can I find out about using them and where to create them.
Global labels connect wires over separate pages; local labels don't leave the page. Find them on the first two "A"s on the right icon bar.
I wondered why you did that what is the difference between the two? [GND vs PE]
Ground is such an over-loaded word! To electronic engineers it means 0V; what other wires are measured from. To power/electrical engineers it means the planet. Sometimes electronic engineers need to reference both so call one GND/0V the other PE (protective earth). In the case of this power supply, a feature is that it is isolated (like it were a battery) which allows us to stack several in series. If one output was attached to PE, it may cause shorts in the thing you're powering or other non-isolated power supplies. Hence, leave it to the user to tie to PE at the front post if he so wishes.
[RE +5V Reference] ? Reference for what? This has me confused.
A power source (vs reference) is meant to supply energy to the circuit. It may be a regulated voltage but isn't expected to be very precise; can vary +/-5% in most cases. A reference is meant to be very stable so it can be used to measure with. In this case, +5V is used to set up the desired current and voltage settings. It's not meant to supply, say, the op-amp power pins.
In HPs drawing is this a mistake? The LM336 has no adjust wire attached what exactly is this doing?
No, HPs drawing isn't a mistake. the LM336 is a fixed 5V zener; adjustment not possible. I substituted it for a TL431 because I had one for the repair to my E3611A and wanted to show it was a viable substitute. You can go with the LM336 if you wish.
The actual HP device has just such a connector. When I looked it up in the symbol library it did not have the yellow rectangle around it. That's when I figured out you must have edited and created it.
Scroll-down, it's there under "Connector_Generic" category. I didn't use any home-made symbols. All of them are out-of-box. That's why I didn't change their default value to a meaningful name.
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Instead of a 431 plus 2 resistors one can also use 2 x TL431 in series for slightly lower noise.
The ICL7107 in principle has a differential input. If you build your own PCB for the converter one can power it from the same supply (with extra regulators from the +-12 V) as the regulator part. It is only the ready made panel meter modules that usually have the negative side linked to the supply.
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pqass
That answers alot of questions and the ground explanation was an eyeopener. I wondered why there was a ground and neg terminal on the front panel. So the ground is earth or protective the negative is just isolated to the device. Is that correct?
What is S+ why a plus if a ground?
The power flag is just to let the program know there will be power on the circuit? Correct? Why does the display and reference need it but not the power circuit?
I think I figured out the labels looking at the properties of yours. I thought one would be an output and one and input but yours were both inputs. ie VMETER were both inputs. I first thought the circuit side would be an output and the plug side an input. So what determines the shape?
Kleinstein good to know about the lower noise.
So the ICL7107 PCB can be designed to eliminate the additional supply without sacrificing device performance? Is that what you are saying?
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Yes one can design a ICL7106/7 circuit that does not need an extra supply just for the display. Just use the differential input of the ICL7107 (most panel meters tie the neg side to the supply or a fixed ref. voltage and for this reason need the separate supply). No complicated circuit (maybe even patch / hack a standard panel meter) needed and essentially the same performance. One may need extra voltage regulators (e.g. +-5 V).
The power flags are for the design rule checks. Some of the symbols like ground or +12 V have an implicite power flag.
The actual DC supply is normally isolated from main ground (PE). The PE terminal is there to allow for the connection (usually to the neg side, but could be the positive side too) by the user.
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The advice and help I have received has led to many improvements. I think I am getting closer to a doable plan. I am sure its not perfect yet but I will get there. I have a bunch of stuff to do for most of the rest of the week. I will be chomping at the bit to get back to this.
Here is the latest rendition. Thanks you guys great.
Therm
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The signal to the current error amplifier is wrong: it should not be - output, but more Tp1. The curretn control signal is also not reaching the regulator.
The regulator supply also has a mistake: ground and the neg side of the rectifier are swaped. There is also a connection missing from the regulator GND pins.
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"... the negative is just isolated to the device. "
Yes the "-" (center) post is the negative to the "+" (left) post; like an isolated, variable "battery". The "⟂" (right) post is the PE connected to the 3rd plug prong, usually the metal case (but not on the E361xA as they are plastic), the transformer iron core (in case a winding touches/burns through to it), and the back metal heatsink.
Without an PE wire, if you were touching the outside metal parts and the an internal mains wire touched it, energy can flow through you to the concrete floor. All mains power has the neutral line attached to the physical earth (via rod) at the power plant and every street pole. It's a shorter path (less resistance) to trip the breaker through the PE wire than you.
What is +S why a plus if a ground?
I have no clue why HP called it that. I just thought I would do the same for continuity. I could have used the GND (▽) symbol everywhere instead but I wanted to convey that all those places that use +S>--- label should be directly attached to the +OUTPUT post (like a "star") since many times GND is just a "pour" (https://en.wikipedia.org/wiki/Copper_pour) over the whole board.
The PWR_FLAG is only a Kicad thing. It's not relevant to the circuit itself. In Kicad, symbol pins have defined purposes: input, output, bi-dir, tri-state, ..., and power in/out. Some symbols have their power pins hidden and kicad automatically connects them to wires (nets) of the same name. DRC complains otherwise. The reference doesn't need a PWR_FLAG because it's only going into (resistor) symbols that have pins defined as "passive" or "input" (not "power in").
BTW: there still is a DRC warning and error in my version. The warning says there are two names for the same net (GND and +S) and it chose +S. The error says I need a PWR_FLAG on the PE wire. But PE is a safety and not a full-time power wire. I ignored the error.
Labels don't really have a direction, however, the way I draw them (my convention) is a hint. If attached on the left of the wire, it's an input. If attached to the right of the wire it's an output. eg. VMETER>--- is input, ---<VMETER is output. I did the latter with the panel meter resistor dividers and the former with pin 4 on the 9-way connector.
So the ICL7107 PCB can be designed to eliminate the additional supply without sacrificing device performance? Is that what you are saying?
WRT the ICL7106/7... most of the panel meters you can buy will probably be based on this chip but it depends on how they breakout the power and sense inputs. Some panel meters "add value" by just providing one pair for power and sense; good for up to 100V. But that won't help you due to reasons noted in my reply#36. I have personal experience with this panel meter (https://www.velleman.eu/products/view/?id=340162) (used in one of my projects) but it wouldn't work correctly/bad readings if the negative sense was connected to the negative supply (though it should work according to Kleinstein). Luckily
after some research (https://www.eevblog.com/forum/microcontrollers/digital-panel-meter-doesnt-work-with-a-power-supply/), I ended up creating a capacitor-isolated supply based on this (https://techlib.com/electronics/regulators.html) (bottom of page; FYI: without lower inverter as it causes glitches). But this won't work for LED displays due much higher current requirement; LCD version only needed <5mA@9V which can be created with a charge-pump PS.
Also, I'm pretty sure the right LED display (showing current on the E361xA) has the sign and most significant digit (+1, -1) removed (just showing 3 whole least sig. digits). I know this because CREF output is a variable negative quantity from 0 to -6V and CREF4METER being 5% of that corresponds to 0.00..3.00A as seen on the display. However, CMETER being from the left of the (R2) shunt will be positive. But both CMETER and CREF4METER are switched by a momentary SPST into the same +V meter input to the 9-way connector; -V meter being +S/GND. You won't have that luxury if you buy an off-the-shelf meter.
Wait 'till you get to understanding how the voltage and current regulation works.
Hint: negative feedback going from each error amp through the diode-OR logic and then the darlingtons back to the error amps.
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WRT the ICL7106/7... most of the panel meters you can buy will probably be based on this chip but it depends on how they breakout the power and sense inputs. Some panel meters "add value" by just providing one pair for power and sense; good for up to 100V. But that won't help you due to reasons noted in my reply#36. I have personal experience with this panel meter (https://www.velleman.eu/products/view/?id=340162) (used in one of my projects) but it wouldn't work correctly/bad readings if the negative sense was connected to the negative supply (though it should work according to Kleinstein). Luckily
Most panel meter boards need a separate supply, as they have the negative input of the ICL7107 chip tied to the the comm pin (internal reference). In a few cases it my ay be linked to supply GND - this would kind of work but could add some offset from ground current and the sign would be wrong. Without this link the ICL7107 has a true differental input and could used a supply (e.g. +-5 V) relative to +S. This supply could than use the same transformer as the OP-amps. To get the right sign one would have the + input of the ICL7107 at the +S side of the shunt and use the negative input of the ICL7107 for the voltage divider or other side of the shunt.
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The signal to the current error amplifier is wrong: it should not be - output, but more Tp1. The curretn control signal is also not reaching the regulator.
The regulator supply also has a mistake: ground and the neg side of the rectifier are swaped.
I should have caught that thanks. I think this fixes it.
I don't understand this part, what is missing? "There is also a connection missing from the regulator GND pins".
Nevermind I spoke soon I think this is it correct?
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See attachment regarding these issues.
A: Fuse on wrong side of transformer.
B: Center-tap of transformer is GND and the negative of the diode bridge goes to the 7912. You have them swapped.
C: 7912 pinout is wrong.
D: Diode on the loose.
E: If these two diodes represent two TL431s then use the correct symbol for TL431 and connect their adjustment pin to their cathode (to program for 2.5V).
F: Use the +S label instead of text.
G: +/- opamp inputs are swapped.
H: Missing junction with +S/+OUTPUT wire (needed for R18 at least). Maybe remove R11 (not populated on the E3610A) and R12 entirely; just attach SW1 pin 1 to left side of R2.
I: Wire from R23 goes to -OUTPUT when it should go to center of R27+R34 divider. Also, R34 looks shorted; wire between pins. FYI: R26+R34 divider is a bit of joke from HP because of the ridiculously tiny 1R/500K ratio. They should've just attached R23 to left-side of R2 and removed R27 and R34 entirely.
J: Don't use broken wires; use a jumper symbol like "Jumper_2_Open".
K: It looks like you removed defined pin 3 when you edited this symbol; looks like lineart just ends. If the PE symbol doesn't attach to a defined pin then DRC will report an error.
WRT the ICL7107... after reading this AppNote (https://www.renesas.com/us/en/document/apn/an9609-overcoming-common-mode-range-issues-when-using-intersil-integrating-converters) several times, it basically says:
you need to supply bipolar power (V+=+5V, GND=0V, V-=-5V), otherwise you'll have to offset the negative sense input via opamp; can't tie it to GND if powered via single-supply. With a purchased panel meter, you don't know if they are generating their own negative supply (and is likely not). Hence the need for an isolated supply for the panel meters.
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pqass and Kleinstein, Thank you for those corrections. Most of what you all pointed out I should have caught. I think I made the corrections properly. If not let me know. Its good to have fresh experienced eyes look sometimes. I have to look in minute detail to find errors, where your eyes see them it seems more instinctively.
pqass I had changed the jumper (JP1) before you mentioned it. I just put x like you said it should be for unconnected wires. But I was thinking couldn't I just eliminate the JP1 wire, it does nothing now?
Also I added power symbols to the outputs is that correct?
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- need GND symbol attached to wire with TP6 for continuity to the transformer center-tap winding.
- U2, U6 GND pins need junction on TP6 wire.
- remove junction to TP6 wire between R32 and R33. Sometimes Kicad puts in a junction when you cross wires and it goes unnoticed.
- WRT U5B, did you edit the symbol to change the pins? Because you didn't need to do that. Remove the symbol and re-add original. Select symbol then right-click mouse > Symbol Unit to B and right-click mouse > Mirror Vertically (or "Y" key) to flip.
- WRT R11, it's actually not 1K but "NO POP" (not populated). And the asymmetry with R12 being a jumper but called R12 is giving me ticks. You could make R12 a resistor symbol with "0R" value.
- "stray hairs" off of CR6 (anode) and R46 (bottom).
- JP1 is technically (from a DRC view) correct. But it sure is odd (from a human view) for not using the open jumper symbol. But yes, I agree to your "... I was thinking couldn't I just eliminate the JP1 wire, it does nothing now?" but then why have JP2 if there's no JP1? My opinion is remove both and tie CR7 cathode to S+.
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- need GND symbol attached to wire with TP6 for continuity to the transformer center-tap winding.
- U2, U6 GND pins need junction on TP6 wire.
- remove junction to TP6 wire between R32 and R33. Sometimes Kicad puts in a junction when you cross wires and it goes unnoticed.
- WRT U5B, did you edit the symbol to change the pins? Because you didn't need to do that. Remove the symbol and re-add original. Select symbol then right-click mouse > Symbol Unit to B and right-click mouse > Mirror Vertically (or "Y" key) to flip.
- WRT R11, it's actually not 1K but "NO POP" (not populated). And the asymmetry with R12 being a jumper but called R12 is giving me ticks. You could make R12 a resistor symbol with "0R" value.
- "stray hairs" off of CR6 (anode) and R46 (bottom).
- JP1 is technically (from a DRC view) correct. But it sure is odd (from a human view) for not using the open jumper symbol. But yes, I agree to your "... I was thinking couldn't I just eliminate the JP1 wire, it does nothing now?" but then why have JP2 if there's no JP1? My opinion is remove both and tie CR7 cathode to S+.
I have done these I will post the revision later. I can just eliminate R12 and replace with wire like the jumpers correct.
Also regarding U5A, I have been fighting those A's and B's ferociously. Now in only four sentences you have ended my struggle. :) Thanks.
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I can just eliminate R12 and replace with wire like the jumpers correct.
Yes but no jumper necessary; just a wire from SW1 pin 1 to left of R2. that's it.
Remove R11 entirely too as it would be pointless.
Also regarding U5A, I have been fighting those A's and B's ferociously. Now in only four sentences you have ended my struggle. :) Thanks.
:)
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Getting closer. :)
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Are you trying to match the original design as closely as possible? Otherwise it might be worthwhile to substitute the opamps with more modern readily available parts.
Compensation may require slight adjustment and can be a bit tricky however.
Maybe also recalculate the resistors so it won't need something rather exotic like 900k or 50k or 2k5 (why is that even?). Shifting E96 to E24 values etc.
Also that's quite beefy low value R46 bleeder there.
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@Therm Mr.
You forgot R16=10K in the original HP diagram. It's between U5B pin 5 and U? (should be U1) pin 6.
Sorry, I've reconsidered my earlier advise (in reply#52) of removing R12 entirely.
By having both R11 and R12 (both resistor symbols) across the R2 shunt, you have the option of populating them both (like in the E3611A) to pick-off a fraction of the shunt voltage drop so as to adapt to your chosen panel meter.
Or, populate R12=0ohm and not populate R11, if your meter can use the full shunt voltage drop as is.
You could change the values for U1 and U4 to:
U1:LF411 as in the original E3610A which you can still buy from Digikey. But even a 741 may work.
U4:LM358 since you can't buy the original LF442 from Digikey any more.
But if you install sockets, then you can change these later in testing.
@ArdWar
HP seems to like odd-ball resistor values; eg. R10=21.5R vs 22K. Most aren't critical and can be nudged to an E12 series (https://en.wikipedia.org/wiki/E_series_of_preferred_numbers#Examples) value.
@Therm Mr. will need to revisit each. He should understand their purpose and what a change in value would have on the circuit.
Non critical: R10, R33, R40, R35 and R36 (can be >0.3ohm and <1ohm), R41, R46.
Likely need to change to adapt to panel meters: R18, R17, R12, R11 Joke: R27, R34 Likely: R27=0ohm, R34=no populate
Critical: R15 (with R37 decides the voltage range on the output), R23 and R24 1% (adapt CREF with R2=0.1ohm shunt voltage drop; in this case 300mV shunt Vdrop=3A when setting CREF=-6V), R22 (probably should match R23).
All the diodes except for CR3 and the bridges can be 1N4148; don't need 180V PIV or >1A diodes here.
CR3 can be a 3A diode like 1N540x where x=1 or greater.
CR9, CR13 bridges can be standard all-in-one 1A 100V bridges or be made from standard 1A diodes like 1N400x where x=2 or greater.
CR2 bridge should be 6A, 100V or better.
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The OP - amps have capacitors in the feedback and the compensation for the regulator is set by those capacitors and the resistors around the op-amps. Substituting another OP-amp type would not change much. If at all to slow an OP-amp could be an issue. A near 1:1 replacement for the LF442 would be a TL062. If it does not have to be DIP case one is free to use more modern types. The current regulator may want a lower drift type (e.g. OPA202 or similar) as the voltage is relatively small.
The resistors R22-R24 should not be that critical. They are for setting the gain for the current regulation and usually the shunt is the weak part. If R22 is needed at all, depends on the OP-amp. With the LF442 or other very low bias types there is no need for R22. The quality / power rating for the shunt can be an issue: The burden voltage is usually a bit on the high side to alow reasonable low drift / noise also with a reduced current. This leads to relatively large self heating and related drift in the current regulation.
In the last plan CREF is still wrong. It should be from the pot wiper.
The meter switching part also still looks odd. Keep in mind that the voltage at Cset is quite a bit larger than the read back case. One would have R23=R24 to get the same scale factor.
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In the last plan CREF is still wrong.
Not sure I see an issue here as the meter gets a fraction of CREF (R20 pot wiper). CREF is meant to feed R24.
I don't know why HP chose CREFs range to be 0 to -6V only for it to feed R24=50K.
They could have instead chose the CREF range to be 0 to -600mV, then R24 would only need to be 5K (or 2 parallel 10Ks) but R23=2.5K would still be an odd duck.
Then R40 may be 100K and R20 would be dialed-in to read 3A on a (0-200mV FS) panel meter when CREF=-600mV.
See attached for this option (simulation here (http://www.falstad.com/circuit/circuitjs.html?ctz=CQAgjCAMB0l3BWcMBMcUHYMGZIA4UA2ATmIxAUgoqoQFMBaMMAKAEMQAWPKsQqwik7h+IYuCRMkYePCix4-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-nYg1-dRf3-IkTwg9pixqUwpjfXNgwGVpcl9ZpcmbFCEMSJtlXQ-tJ09Dp+DMM8AUcYhnBvf4QC8XxAlCR990iQ8ODfBwUIccQwEkbjz2+BRFEQbAikIMA8AQDBiD6TI+OyMMJmVVCXzERTOOrPAnRoCd5jIBkxC6UVGmcCN9OSUVdPAftdBRGBAxVaBNSNCy7Qs307KyABlUy8ikqlCV5AUhV0FBlN81FkjCwytInMZXM4rpiSA81zOVQyWAADzEf88EtGROGkSAkBeLY4AAW3OAAdZlzgAE1mAB7A0KoqgA7eqeSqq4UCq5kAAsAFcWoAFwysRiEtUxPjAbBxFMAYRBACqDQ8gB6ABVTg-CW84AEsWqqg16r2kagA)).
Of course R33 and R28 would change by x10 but the R31,R32 trimmers and R19 10 turn pots could still be 10K.
With my alternate 0..-600mV CREF, R24/R23 could also be 10K/(2 parallel 10K); no odd values.
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Indeed, the Cref part looks OK. I somehow mixed up the pot and trimmer for the full scale.
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R17 and R18 should be ratio, so the usual 1:9 pair of 20k:180k or 30k:270k should be fine. A bit higher quiescent current, but shouldn't be a problem.
R23 and R24 appears to be ratio too. 1:20 are plenty. 1k:20k, 1k1:22k, 1k2:24k, 1k5:30k, 1k8:36k, etc.
R22 looks like attempt to balance out bias current. Make it equal R23, or even just leave it out when using low bias opamp.
It seems that you can get away with 15k on R15.
Any resistor in series with potentiometer are obviously noncritical. R33 could be 3k3; R40 could be 270k (maybe, not sure which range R20 is usually in); R10 could be 22R; R6 just pick whichever low value resistor available tbf.
R27 and R34 seems unnecessary. Just pick random low value R27 and random high value R34 if you insist.
Just put 4k7 for R41.
While at it, let's see if you can get away with higher value for R46. 390R dissipates 1.5W at 24V output...
C7 having different value from C13 is also rather curious. Did they do that as an attempt at power sequencing?
If you're changing CREF scaling, might as well change 5VREF to 2V5 so it doesn't need two TL431. Of course you need to recalculate R15 R23 R24 for that.
Honestly this CREF and dual range business is making things way more complicated for not much benefit. Constant current control could be much simpler without CREF, just like how it's done in 3620 (and practically everyone else).
As for OPAMP, I'm not sure tbf. TL062/072/082 sounds adequate, but I'd like something with lower offset here.
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The 2 ranges for the current setting make some sense, kind of an alternative to a 10 turn pot. One quite often needs current limits well below the full capability of the supply.
There is no real need to overdo it with the resistor accuracy in the set part, as there is anyway the pot to set the values. It would only be the read back part that may want reasonable stable / accurate resistors. For the voltage regulator the offset of the OP-amp should not be that relevant. So a TL071 is OK there. It is mainly the current part that may want low offset / low drift, so that the reading of the set point has not to much offset from the final actual current limit.
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That's correct with the pot choice.
most times it's a flvour of how one likes the (daily) use of the lab supply:
- 10 turn pot in easier to build in because you only have one hole in the frontpanle and save the space there. Negative aspect for use is you have to turn and twiddle several turns to get over the (full) range -- sometimes one prefers to reduce the current quick when the magic smoke vents from the powered device.
- 2 pots is quick for course /fien seup - and as kleinstein mentioned, modern circuits often want a precise limit in the low current range for some tests. A "one suits all" are dual pots that have a dual-shaft concentric (e.g. BOURNS
81A2A-B28-D15/D15L) -- but of course hard to get or quite expensive.
For my projects I prefer BOURNS 3680, most because the FAE here dropped me 100 pieces for free evaluation.
One thing for the lab supply to keep in mind: ON/OFF output switch to quick unpower the output.
Especially when you have a dual/muti voltage supply .-)
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But the 2 range on 3610 is not for that. It is there to extend the I/V curve by allowing higher current when supplied with lower voltage.
The two ranges are 3A/8V and 2A/15V (or 0.85A/35V and 1.5A/20V), so you need multiturn for control regardless.
For coarse-fine control you can just put two pots with one or two order of magnitude difference in series. Especially here since all of the controls are in rheostat configuration. A bit ugly but shouldn't be a big problem for DIY.
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Getting closer. :)
If you will be testing the design on a breadboard, consider connecting R6 to the ORing node instead of directly to the output of the CV opamp. This idea suggested to me by Kleinstein greatly reduced the voltage overshoot in my PSU design whenever it transitioned from CC to CV mode.
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Are you trying to match the original design as closely as possible?
Yes Am trying to replicate original design because its proven quality and works well. But there are a few components that will have to be substituted due to obsolescence.
Thanks for the advice
Therm
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@Therm Mr.
You forgot R16=10K in the original HP diagram. It's between U5B pin 5 and U? (should be U1) pin 6.
Sorry, I've reconsidered my earlier advise (in reply#52) of removing R12 entirely.
By having both R11 and R12 (both resistor symbols) across the R2 shunt, you have the option of populating them both (like in the E3611A) to pick-off a fraction of the shunt voltage drop so as to adapt to your chosen panel meter.
Or, populate R12=0ohm and not populate R11, if your meter can use the full shunt voltage drop as is.
You could change the values for U1 and U4 to:
U1:LF411 as in the original E3610A which you can still buy from Digikey. But even a 741 may work.
U4:LM358 since you can't buy the original LF442 from Digikey any more.
But if you install sockets, then you can change these later in testing.
@ArdWar
HP seems to like odd-ball resistor values; eg. R10=21.5R vs 22K. Most aren't critical and can be nudged to an E12 series (https://en.wikipedia.org/wiki/E_series_of_preferred_numbers#Examples) value.
@Therm Mr. will need to revisit each. He should understand their purpose and what a change in value would have on the circuit.
Non critical: R10, R33, R40, R35 and R36 (can be >0.3ohm and <1ohm), R41, R46.
Likely need to change to adapt to panel meters: R18, R17, R12, R11 Joke: R27, R34 Likely: R27=0ohm, R34=no populate
Critical: R15 (with R37 decides the voltage range on the output), R23 and R24 1% (adapt CREF with R2=0.1ohm shunt voltage drop; in this case 300mV shunt Vdrop=3A when setting CREF=-6V), R22 (probably should match R23).
All the diodes except for CR3 and the bridges can be 1N4148; don't need 180V PIV or >1A diodes here.
CR3 can be a 3A diode like 1N540x where x=1 or greater.
CR9, CR13 bridges can be standard all-in-one 1A 100V bridges or be made from standard 1A diodes like 1N400x where x=2 or greater.
CR2 bridge should be 6A, 100V or better.
I don't know how that rascally R-16 escaped but thanks. I will undo the R12 change. The component advice will be helpful too. My schedule is been busy right now and my time limited but next week I will be back at it 100%. Choosing a display is something I need to do to move on.
Thanks
Therm
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andrewtaylor That bourns is quite interesting. Thanks for posting.
xavier60 Yes I will be testing on breadboard. If the smoke is going to fly, I want it to happen when its easy to fix.
Kleinstein as always your help is appreciated.
Thanks everyone
Therm
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I have made the change-backs you recommended pqass.
I do plan on dip sockets because it will absolutely prevent burning up those chips soldering and provide changeability. I am pretty sure I could solder the chips without a problem. If a different footprint chip that is direct solder were better I am open to that.
Kleinstein why the TL062?
Regarding the ICL 7107 based panel meters is there a particular spec or version I am looking for? Like 0-15v 0-3a or is that not a factor? The expense is less of a concern to me than quality. I don't expect this project to be a bargain.
R19 calls for a 10k 5% 10-turn Cermet and R37 calls for a 50k 5% 10-turn WW. I found both relatively easily but there is a spec for linearity what is that? Is that a factor I need to be concerned with.
As mentioned before in this thread (by pqass I think), the HP has a very large aluminum heatsink that is basically the whole back panel of the device. The Darlingtons were mounted on a small porches on each end of the heat-sink. I know there will be a lot of heat to reject. I plan on mounting the Darlingtons on small aluminum heat-sinks maybe even fan cooled if that's even possible (I don't know). At minimum I planned on a cased mounted fan to circulated air through the cabinet. Maybe even get fancy a use a thermistor circuit to control a fan. I would have to research that a bit. I don't want to have a heat issue. Is this over kill?
What do you guys think?
Thanks
Therm
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The TL062 is an easy to get part near identical to the LF442. From the performance it is not the best however. For better stability with the current I would consider a OPA2202, however like many newer chips it is only available in SMD and would need an adapter to use on a breadboard or in a DIP socket. If it has to be DIP, maybe an RC4558 could be an option.
For the ICL7107 / TC7107 there should not be much difference between versions / manufacturers - they should all be OK. The display is 1999 counts. So a voltage range like 24 V or 30 V would not be ideal, as less of the range is used. 3 A is not ideal for the display, as the resolution would be 10 mA. Getting a 2nd range is however also a bit tricky. It is more effort (extra BCD-7 seg driver), but the ICL7135 version may be an option too.
For the trimmers the accuracy is not that important. One usually reads the voltage from the display and less from the scale at the pot. A highly linear 10 turn pot would mainly make sense if used with a dial indicator to read the set value.
One would definitely need a large heat sink, especially if no tap switching is used. For 3 A and 15 V range the raw DC voltage would be at some 20-25 V or a bit more. This would be some 60-75 W to dissipate worst case. Small heat sinks would need a larger fan. The safe way is a sizable heat sink and a fan as back-up.
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Hi @Therm Mr.
You picked a difficult design to start with. The reason being, it is generic for a range of Agilent power supplies from 8vDC to 120vDC. The circuit diagram tries to cover all models so is difficult to follow for one specific model, eg E3610A, because a lot of the parts are redundant.
You may have this already but there is a table that lists the different components between the models.
I may be interested in building the E3610A version too so I will be following your progress.
enut11
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Hi @Therm Mr.
You picked a difficult design to start with. The reason being, it is generic for a range of Agilent power supplies from 8vDC to 120vDC. The circuit diagram tries to cover all models so is difficult to follow for one specific model, eg E3610A, because a lot of the parts are redundant.
You may have this already but there is a table that lists the different components between the models.
I may be interested in building the E3610A version too so I will be following your progress.
enut11
Thanks for the sheet. I know the design is difficult that partly why I chose it.
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I ran the rules checker due to my thinking I was in fairly good shape. I was wrong it found 13 errors and 77 warnings. some of the warnings were edits, like switches and the power plug. Also I had U5 LM393 and U4 warnings. I had used dual op-amp instead of just LM393 it was split between 393 and TLZ something. So I was getting pin errors and also unit C not placed error?
So Trying to fix this I remembered my A, B lesson from @pqass. I deleted all and re-inserted from the library. Then I found that I was not getting the 4 and 8 pins. And I discovered they were option C. So I added the pins with the C option to the correct half of the op-amp and thought I was good. re-ran the checker still getting errors. Different ones. They are "Duplicate items UC" on U4B and U4A "unplaced units" [UnitC]. U5A says the same unplaced units error.
Also many Warnings: Symbol pin or wire end off connection grid. I'll include a screen shot. There are other things I need to look at but I figured I would start here.
Thanks
Therm
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So Trying to fix this I remembered my A, B lesson from @pqass. I deleted all and re-inserted from the library. Then I found that I was not getting the 4 and 8 pins. And I discovered they were option C. So I added the pins with the C option to the correct half of the op-amp and thought I was good. re-ran the checker still getting errors. Different ones. They are "Duplicate items UC" on U4B and U4A "unplaced units" [UnitC]. U5A says the same unplaced units error.
Make sure you've deleted all units first (A, B, C-power pair) from previous Adds.
Then Add back "LM358" under "Amplifier_Operational", placing all three (A, B, C) units. Similarly for "LM393" under "Comparator".
Place power symbols on C units and change the reference to replace "?" with the appropriate number.
The C units don't have to be placed over-top an A or B unit. Some people put them off to a corner with bypass caps.
Also, make sure you don't have any "?" remaining in a reference anywhere. Use Cntrl-F to find "?".
Then run DRC.
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Regarding the ICL 7107 based panel meters is there a particular spec or version I am looking for? Like 0-15v 0-3a or is that not a factor? The expense is less of a concern to me than quality. I don't expect this project to be a bargain.
...
As mentioned before in this thread (by pqass I think), the HP has a very large aluminum heatsink that is basically the whole back panel of the device. The Darlingtons were mounted on a small porches on each end of the heat-sink. I know there will be a lot of heat to reject. I plan on mounting the Darlingtons on small aluminum heat-sinks maybe even fan cooled if that's even possible (I don't know). At minimum I planned on a cased mounted fan to circulated air through the cabinet. Maybe even get fancy a use a thermistor circuit to control a fan. I would have to research that a bit. I don't want to have a heat issue. Is this over kill?
I'm searching Google Shopping or Amazon for "digital panel meter". There are so many that aren't useful to your application. Like:
- 2 wire only; only good for 2.5VDC to 100VDC
- AC input
- ammeters with built-in shunt or AC current transformer (torroid)
- combination voltmeter and ammeter
- frequency meter, tachometer, counter
For those that have a power pair (5VDC) AND a sense wire (single or pair), no information is provided on how to configure it or about power isolation with regards to the sense inputs. Ideally, you need a meter with a separate power pair AND 0-200mV (full-scale) sense inputs (with IN-LO/-Vsense that can be tied to supply ground). Most people won't know how to configure the resistor divider for their application, hence, you'll see 5, 20, 50, 100, 200, 500V in the description.
You can find exactly what you need for name brand meters like the Murata (https://docs.rs-online.com/5f16/0900766b8133cebc.pdf) DMS-20PC series (https://www.murata.com/products/productdata/8807022329886/20pc.pdf) but then you're looking at >$60!
As I'd said earlier, an ammeter is just a voltmeter that measures across a shunt so you can buy the same panel meter to do both power supply output voltage monitoring and ammeter service. We don't want to add another shunt (for reasons see my reply#36) as we already have R2.
However, hope may not be lost if we take a bit of a gamble.
If you search for "digital panel meter 5135" you'll see the attached. They are sold by many suppliers like this one (https://www.amazon.ca/Fafeicy-5135A-Voltmeter-Digital-Panel/dp/B08DL175KY/ref=sr_1_7?crid=3UQBXE5GS3L2L&dib=eyJ2IjoiMSJ9.T1-3kG3aqhlP3BZC7nwCU3SLzium-M6cl3Ohd8m7ra_ifObh6hpKYCfSxENhDVZCr56Zu5kyYDRIGQt8Ncv9-uuXXUYKURZqQybUBMYcgIXnlY_0-U8KBwm27HtLLRLOg4V3pJUC6RFbeXJPa-fNLDTRzpWpFM9BwOgUK5ofEUDVZGuCkQB0eA0xbdFKwcTzZaFK-tbGztoomJHq4BJAbhOtEO61hxy3yp5xnClM_hR8JlkS0nEvv14zhWUOwzLb09mCeEGyEMftHvEy60LrgMgDMd7B3SkoqdisJfzM2jc.1eyTs9UbaPwJwRN-TqQZy5fIt3a_gNJhX1nQVbz55Bo&dib_tag=se&keywords=digital+panel+meter&qid=1719243695&s=industrial&sprefix=digital+pan%2Cindustrial%2C158&sr=1-7). According to the ICL7107 datasheet (https://www.renesas.com/us/en/document/dst/icl7106-icl7107-icl7107s-datasheet), Figures 13, 14, IN-LO/-Vsense can be connected to GND if it has an external reference (TL431 seen in another photo) and -5V supply is provided, both of which may be true in the photo.
To use this meter, you'd just need a 7805 similarly configured like the 7812 from the same transformer's unregulated positive in the op-amp supply; no need for another isolated 5V display supply. DO NOT USE the +5VREF label to power the panel meters.
For the ammeter configuration up to 1.999A, R12=0R (a short), R11=open/no populate. For one up to 19.99A, R12=10K, R11=100K. Short the "2" or "20" option on the panel meter to enable the correct decimal point (0-1.999A vs 0-19.99A). IN-HI of the meter is on the common of SW1A switch, IN-LO on [+S]/GND/+OUTPUT post. HOWEVER, R20 wiper is a negative voltage! To turn it positive, you'll need an inverting opamp. See attached panel meter wiring schematic.
The voltage monitor panel meter can also use the same op-amp power supply's new 7805 positive output and GND. With IN-LO tied to [+S]/GND/+OUTPUT post and IN-HI tied to the R18=10K/R17=900K divider. HOWEVER, it too will report a negative voltage, thus, another inverting opamp will be needed. See attached panel meter wiring schematic. Short the "20" option on the panel meter for 0-19.99V.
WRT heatsinks...
CPU heatsink+fans can transfer lots of heat in a compact space.
Attach on back of enclosure or at least exhausting the fan out the back.
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Make sure you've deleted all units first (A, B, C-power pair) from previous Adds.
Then Add back "LM358" under "Amplifier_Operational", placing all three (A, B, C) units. Similarly for "LM393" under "Comparator".
Place power symbols on C units and change the reference to replace "?" with the appropriate number.
The C units don't have to be placed over-top an A or B unit. Some people put them off to a corner with bypass caps.
Also, make sure you don't have any "?" remaining in a reference anywhere. Use Cntrl-F to find "?".
Then run DRC.
Done and worked. So my mistake was deleting the reference to C. Thanks easy fix.
You can find exactly what you need for name brand meters like the Murata DMS-20PC series but then you're looking at >$60!
I saw these and was going to ask about them. I am ok with the $60 just knowing they are quality and will work no problem. Thanks for this too.
WRT heatsinks...
CPU heatsink+fans can transfer lots of heat in a compact space.
Attach on back of enclosure or at least exhausting the fan out the back.
Would this be enough with another fan venting the case? Or could I just configure this to vent out the case?
https://www.ohmite.com/assets/docs/sink_c40.pdf?r=false (https://www.ohmite.com/assets/docs/sink_c40.pdf?r=false)
pqass Thanks Again
Therm
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See digikey here (https://www.digikey.com/en/products/filter/panel-meters/meters/805?s=N4IgjCBcoLQExVAYygFwE4FcCmAaEA9lANogCsI%2BAnCALoC%2B9%2BCkpAIgLIDK8ADAAoBhGLzr4AbIhABLACZQQMMLwj4ADqgWUQqAJ5rsCgIYBnFIyA) for the DMS-20PC-0 (200mV) version; just pick your color.
See Figure 2 arrangement here (https://www.murata.com/products/productdata/8807022329886/20pc.pdf) with external R12/R11 or R18/R17 divider.
You'll still need the inverters and wiring configuration as per my last post.
EDIT: If you're going to use the Murata panel meters, they state "Devices are fully calibrated at the factory...and never require calibration or adjustment." This is a problem since the values or R12/R11 and R18/R17 are pretty loose and are relying on the panel meter pot to calibrate. Since this isn't possible with the Murata meters, you'll have to make R12/R11 10:1 and R18/R17 100:1, exactly. The only case where this isn't necessary is if R12=0R and R11=open/no populate.
EDIT2: Okay, you can still go loose with the R12/R11 and R18/R17, if you add pots between the two resistors or between the 10Ks in the inverters. See attached. And the CREF4METER calibration pot isn't really necessary as you can tweak R20. But I earlier forgot that the CREF4METER has to be divided by 2 (see parallel 10K).
If you form a tunnel (with two half-heatsinks; see your link), the fan can pull inside air through the tunnel out the back. The fan mounted between tunnel and inside back of your enclosure.
If you are only using one of those heatsink halves, you can cover the tops of the fins with an Al plate, with fan mounted in the center of the plate. Then air can enter from either side, turn 90° through the center and out the back of the enclosure.
I don't think you'll need another fan as the bulk of the heat is from the series pass transistors.
You'll need openings on either side or top/bottom of the enclosure near the front for air intake.
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I plan on mounting the Darlingtons on small aluminum heat-sinks maybe even fan cooled if that's even possible (I don't know). At minimum I planned on a cased mounted fan to circulated air through the cabinet. Maybe even get fancy a use a thermistor circuit to control a fan. I would have to research that a bit. I don't want to have a heat issue. Is this over kill?
What do you guys think?
Thanks
Therm
@Therm Mr.
I have used this simple 2-transistor circuit to provide temperature based cooling in a power supply. Choice of active components is not critical.
Use a 10K thermistor at J9 and 12v fan at J10. Adjust RV5 to suit your fan and the temperature where it starts.
Thermistor is mounted close to a power transistor on the heat sink.
enut11
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Meters: eBay item number: 355659784116
This compact 4 digit 10A panel meter has a 1mA resolution. Basic accuracy is 0.5% but I see an IR pot on the back which suggests it can be trimmed.
Shunts in these meters are normally in milliohms so have minimal impact on voltage regulation.
I have not looked but there is likely a matching 4d voltmeter.
Cost is ~$17 AUD
enut11
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There are many cheap meter modules available. The problem is that they in most cases have the measured voltage / current linked to it's supply. In this case they will likely need a separate transformer or similar. There may be a way to shift the signal with a difference amplifier and use a voltage reading module with the same supply as the regulator. One just has to find a suitable module.
Even if only a few 10 mOhm, one usually does not want an extra shunt outside the regulation loop. If anyway using a separate supply one could as well place it in the loop.
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I have eliminated most of the warnings. But the power Outputs are actually inputs in the symbol library. I can find no Output symbol.
@pqass My Output neg gives a "not driven by any output power pins" warning.
Output+ "Both S+ and +VDC are attached to same items; S+ will be used in the netlist".
Also it does not like ground and S+ attached to same line.
Can I just ignore these?
Also A whole bunch of Warnings "symbol or pin not connected or wire end off grid". But they are connected they just not one continuous line they overlap on the ends without a connection dot.
Can I ignore these also?
Thanks
Therm
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There are many cheap meter modules available. The problem is that they in most cases have the measured voltage / current linked to it's supply. In this case they will likely need a separate transformer or similar. There may be a way to shift the signal with a difference amplifier and use a voltage reading module with the same supply as the regulator. One just has to find a suitable module.
Even if only a few 10 mOhm, one usually does not want an extra shunt outside the regulation loop. If anyway using a separate supply one could as well place it in the loop.
I plan on the display supply having it's own transformer. Something like a small 24v. I am still weak in my knowledge of the display section and all its little details. But I'm learning.
Thanks
Therm
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I have used this simple 2-transistor circuit to provide temperature based cooling in a power supply. Choice of active components is not critical.
Use a 10K thermistor at J9 and 12v fan at J10. Adjust RV5 to suit your fan and the temperature where it starts.
Thermistor is mounted close to a power transistor on the heat sink.
enut11
Thanks I like that
Therm
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See digikey here (https://www.digikey.com/en/products/filter/panel-meters/meters/805?s=N4IgjCBcoLQExVAYygFwE4FcCmAaEA9lANogCsI%2BAnCALoC%2B9%2BCkpAIgLIDK8ADAAoBhGLzr4AbIhABLACZQQMMLwj4ADqgWUQqAJ5rsCgIYBnFIyA) for the DMS-20PC-0 (200mV) version; just pick your color.
See Figure 2 arrangement here (https://www.murata.com/products/productdata/8807022329886/20pc.pdf) with external R12/R11 or R18/R17 divider.
You'll still need the inverters and wiring configuration as per my last post.
I will look at that wiring soon and try to grasp it. I love having this thread as a reference to refer back to.
EDIT: If you're going to use the Murata panel meters, they state "Devices are fully calibrated at the factory...and never require calibration or adjustment." This is a problem since the values or R12/R11 and R18/R17 are pretty loose and are relying on the panel meter pot to calibrate. Since this isn't possible with the Murata meters, you'll have to make R12/R11 10:1 and R18/R17 100:1, exactly. The only case where this isn't necessary is if R12=0R and R11=open/no populate.
EDIT2: Okay, you can still go loose with the R12/R11 and R18/R17, if you add pots between the two resistors or between the 10Ks in the inverters. See attached. And the CREF4METER calibration pot isn't really necessary as you can tweak R20. But I earlier forgot that the CREF4METER has to be divided by 2 (see parallel 10K).
This is going to take a bit for me to completely comprehend. But I will eventually get it it. Thanks for the education.
If you form a tunnel (with two half-heatsinks; see your link), the fan can pull inside air through the tunnel out the back. The fan mounted between tunnel and inside back of your enclosure.
If you are only using one of those heatsink halves, you can cover the tops of the fins with an Al plate, with fan mounted in the center of the plate. Then air can enter from either side, turn 90° through the center and out the back of the enclosure.
I don't think you'll need another fan as the bulk of the heat is from the series pass transistors.
You'll need openings on either side or top/bottom of the enclosure near the front for air intake.
I intended to use two one for each Darlington. Better too cool than not cool enough. :) Also I will put some vents in the case. You can't push air out that you don't pull in. :) I will configure the fan so it is mounted at the back-plate of the case. Will the PCB layout portion of KiCad allow me to place those heatsinks without interfering with the trace?
Thanks
Therm
PS one last thing. The parts list lists resistor types PWI, PWN, MO and TF. I know TF as thin film and MO metal oxide. The others have me a bit perplexed. Can anyone offer any clarity on this.
Also C2 is listed as a 1000uf and a 10000uf. I am thinking the 10000 is the right choice am I correct?
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I have eliminated most of the warnings. But the power Outputs are actually inputs in the symbol library. I can find no Output symbol.
@pqass My Output neg gives a "not driven by any output power pins" warning.
Output+ "Both S+ and +VDC are attached to same items; S+ will be used in the netlist".
Also it does not like ground and S+ attached to same line.
Can I just ignore these?
Also A whole bunch of Warnings "symbol or pin not connected or wire end off grid". But they are connected they just not one continuous line they overlap on the ends without a connection dot.
Can I ignore these also?
Thanks
Therm
There should be only one name for +S, GND and +output. If additional names are wanted use just text elements (e.g. for + output).
The wires of grid are a bit anoying. This may happen from diagonal movements. To clean up it is often easiest to remove the effecte wire and redraw.
The wire not connected part should be fixed if later a PCB is planed. Sometime just move the part to the side and back to where is was to get it connected.
Chances are that PCB mounted heat sinks are too small for the main regulator (the 2 darlingtons / MOSFETs). They can be OK for auxiliary regulators (e.g. +-12 V), the display +5 V and the rectifier.
The main heat sink(s) are usually too large and more a PCB mounted to the hea sink, using the whole back side of the PCB and the power parts moutned below, with the heat tap down and a mount hole in the PCB.
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@pqass My Output neg gives a "not driven by any output power pins" warning.
Output+ "Both S+ and +VDC are attached to same items; S+ will be used in the netlist".
+VDC and -VDC symbols are from the "Power" library so they have their pin defined as "Power input". That's why there's a complaint about needing the "PWR_FLAG". ie. a complaint that a pin needs power but no source was identified. If you really like the large + and - symbols that much, you can make a copy of them in your own library and change their Electrical Type to Passive.
You can ignore the "Both S+ and +VDC..." warning; it'll just pick one for a net name. It's required to attach GND (from the op amp power supply) to the +OUTPUT post otherwise the circuit won't work.
I plan on the display supply having it's own transformer. Something like a small 24v. I am still weak in my knowledge of the display section and all its little details. But I'm learning.
But it isn't necessary. You could just hang a 7805 from the same transformer as the 7812.
The DMS-20PC models require a +5VDC regulated power source; 24V to 5V is quite a drop for a 5V regulator.
Will the PCB layout portion of KiCad allow me to place those heatsinks without interfering with the trace?
It's called a keepout area. After placing, adjust its Properties to also keepout copper fill and footprints.
PS one last thing. The parts list lists resistor types PWI, PWN, MO and TF. I know TF as thin film and MO metal oxide. The others have me a bit perplexed. Can anyone offer any clarity on this.
My guess: PWI=power inductive, PWN=power non-inductive, MO=metal oxide, TF=thin film
Also C2 is listed as a 1000uf and a 10000uf. I am thinking the 10000 is the right choice am I correct?
It's 10,000uF. I saw that error too.
Also,
I've updated the panel meter wiring schematic for 200mV full-scale panel meters. See attached.
Changes from the last version are:
- R17 increased to an E12 series value,
- R12/R11 values reflect monitoring for up to 3A,
- removed need for R20 and R40, as CREF can be used directly in the 200:1 inverting amp configuration,
- added calibration pots for CREF, CMETER, VMETER to adapt to 200mV full-scale panel meters that are factory calibrated; that don't have their own calibration pots,
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Dividing the signal for the current and voltage so far down is not ideal. This would make it sensitive to amplifier offset and drift, so that the LM324 is no longer acceptable. The linked display modulte from DK at least has a differential input, otherwise the ground shift form a common link for power and ground could be another problem.
The display inverter circuit could likely get away without the extra buffers at the input, so just 1 amplifier for voltage / current.
I would consider getting a cheap module from ebay (e.g. there are some with voltage (100V) and current combined), to use an external shunt / suitable range (e.g. 1 or 2 V for the voltage).
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So today I decided to open my E3611A to find out what's on the display board. I just found the expected (pair of) TC7107CKW but also a TSC9491 1.22V voltage reference; and no other chips. Much to my surprise though, the 7107 was configured for 2V full-scale; not the 200mV that I'd assumed! I confirmed this by checking the voltage between 7107 V+ref and V-ref pins which showed 1.00V; not 100mV.
This makes sense given, in the E3610A, the 1:1 current divider R12=0R/R11=open and 10:1 voltage divider R18=100K/R17=900K. With a 2V full-scale meter, 3A looks like "3.00", and 15V (max for the supply) looks like "15.00". I'm assuming (uh oh) my E3611A display board is virtually identical to the E3610A or E3612A in all but which decimal digits are enabled. My E3611A has a 100:1 voltage divider and thus has only 100mV voltmeter resolution.
Given what Kleinstein said about working with small voltages, we can avoid them by choosing 2V full-scale panel meters like the Murata DMS-20PC-1 (last digit changed). However, if choosing a generic panel meter like the "5135" that I proposed, it likely won't be possible to change the reference voltage to 1V. And the most you could do is modify it to 200mV full-scale (by removing the RA resistor). Actually, I'm not so sure anymore what the reference might be on some of these DC5V, 20V, 50V, etc panel meters.
Furthermore, the set current (CREF R20 wiper) is negative vs actual current (CMETER) but the way the E361xA series power supplies skirts this is by dropping the "+1" left digit, which you won't be able to do with a purchased panel meter. Also, I believe the only reason negative voltmeter readings aren't shown is due to the floating supply allowing IN-LO and IN-HI being tied to R18/R17 center point and +S/GND/+OUTPUT post, respectively. If you drop the isolated display supply requirement, I believe an inverting amp is necessary since meter ground will be tied to +S/GND/+OUTPUT post.
Unfortunately, with a 2V full-scale panel meter, the CMETER divider would be R12=0R/R11=open/no populate, which means we won't have an opportunity to fit a calibration pot. As such R2 (0.1R) would have to be very accurate or at the least slightly higher, which would at least give us the opportunity to put a high-value resistor in parallel to adjust it down to exactly 0.1R.
The brain hurts from too many trade-offs to consider.
@Kleinstein
It's true that the LM324 unit A buffer isn't needed as CREF is already driven by opamp U4A, thus CREF can be tied to the first resistor in the inverting amp. However, I believe VMETER (R18/R17 divider center) requires a buffer (unit C) into its inverting amp, otherwise the transformation won't be correct.
Even-though the LM324 (powered by a +/-12V supply) would be working with small voltages (<30mV), the op amp inputs never come close to the rails. If there is (crossover) distortion close to 0V maybe another op amp like the TL074 would be more appropriate.
Attached you will find another wiring revision for 2V full-scale panel meters (vs for 200mV FS meters in my previous post).
Changes are:
- R12=0R/R11=open/no populate, the entire R2 Vdrop goes directly to the panel meter.
- Addition of a high-value resistor in parallel with R2 for the option to lower R2 to exactly 0.1R; can't increase it.
- CREF inverting amp is now at a modest 20:1; changed to 100K (left resistor).
- R18=100K/R17=1M is now at a modest 11:1; changed R18.
- VMETER inverting amp remains 1:1 except for the calibration pot raised to 2.2K.
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There are many cheap meter modules available. The problem is that they in most cases have the measured voltage / current linked to it's supply. In this case they will likely need a separate transformer or similar. There may be a way to shift the signal with a difference amplifier and use a voltage reading module with the same supply as the regulator. One just has to find a suitable module.
Yes, that's correct.
One point not mentioned yet:
Most of the digital panel meter cause a lot of EMC noise.
I don't want this in my lab bench supplies, That's why I prefer analogue (moving coil DC) meters.
No noise, no EMC -- and no need for a seperate power supply to power the meter.
When I really need to read out the voltage with higher precision, I use external HP 34401 or Fluke 87 V, whatever is handy.
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For the EMI / supply interference it depends on the panel meters. Some can be rather bad, with a switched capacitor circuit to generate a -5 V supply. The other point is a multiplexed LED display with some (not with an ICL7107).
The problem with using the LM324 with small voltages it not gettting close to zero or cross over. The problem is the offset voltage ( ~ 5 mV ) and it's drift. It gets better with a 2 V range, or if only 200 mV available a divider just at the input to the module. For the current one may have to make sure to have the shunt close to the output, not to have too much cabeling included with the shunt.
I don't think the current display would want the inverter. One could consider a difference amplifier to allow a proper connection to the shunt.
The voltage sense can use the inverter directly from the neg. side, without an extra voltage divider. So as an active divider, separate from the feed back the an regulator.
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I am really wanting to move on to the panel meter but this rules checker is getting the better of me. I have been able to eliminate most errors but the warnings will not go away no matter what I do. It tells me there are no connections where there are connections. What am I doing wrong? See Pic
Also S1 has an A and B and so does S2 and this seems to produce errors. Though I see no way to split the switches like the op-amps.
I am really enjoying the discussion on the panel meters. It seems like it may even be the hardest most complex part of the project.
@andrewtaylor I have a fluke 87 also. I have had it for decades great meter.
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See attachment regarding these issues.
A: R41 connected to the wrong wire. It should be connected to U5A pin 2.
B: "stray hair"; unconnected wire or symbol with no wires attached. Remove it or terminate with the "no connection" flag (see icon bar on right).
C: "SW1" appears twice as a symbol reference. One should be SW1A and the other SW1B to signify there are two ganged switches.
D: PWR_FLAG is not a connector. You need a connector symbol here. But don't choose from the Power library (like the +VDC/-VDC from before) as they have Power Input electrical type and demand a PWR_FLAG on the wire.
E: Wire is connecting to the line graphic. It should be connected to the green wire below it, where R12/R11 meet.
F: Delete the wire from junction to VMETER and re-add it. There may be a broken connection along the path.
Also, not identified with a letter is T2 pin 2, loose junction and/or wire. Delete whatever is there and re-Add.
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The problem with using the LM324 with small voltages it not gettting close to zero or cross over. The problem is the offset voltage ( ~ 5 mV ) and it's drift. It gets better with a 2 V range, or if only 200 mV available a divider just at the input to the module. For the current one may have to make sure to have the shunt close to the output, not to have too much cabeling included with the shunt.
I don't think the current display would want the inverter. One could consider a difference amplifier to allow a proper connection to the shunt.
The voltage sense can use the inverter directly from the neg. side, without an extra voltage divider. So as an active divider, separate from the feed back the an regulator.
But wouldn't any offset be compensated by the calibration pot (in the inverting amp)?
With a 2V full-scale meter each right-most digit is a mV. With a 200mV full-scale meter each right-most digit is a 100uV.
So rather than the LM324, do you have any recommendations on an op amp with low (temperature induced) drift?
Actually, the CREF inverting amp is not strictly needed. If the user is okay with seeing a negative current value when the CC Set button is pressed vs. when actual current is being displayed. The J1 connector has both + and - pins for panel meter IN-HI and IN-LO so they can be twisted and attached close to the source; shunt divider or R20 pot, if not using an inverting amp.
My reasoning for using an inverting amp on VMETER is because I don't think you can tie IN-HI to +S/GND/+OUTPUT post and IN-LO to the R18/R17 divider center if the panel meter power isn't floating. That is, can't do that if power meter GND supply is tied to the +S/GND/+OUTPUT post. So if I'm wrong here, and the user is okay with seeing negative currents when CC Set button is pressed, then no inverting amps are needed at all.
The regulator feedback dividers are actually R15/R37 (for voltage) and R24/R23 (for current). R18/R17 and R12/R11 are just for the panel meters.
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The pots are for the scale factor, not for the offset. A low offset variant of the LM358 is the LT1013. The classic low offset amplifier is the OP07. If SMD (e.g. SO8) is not a problem, I would use the newer OPA202 / OPA2202.
Even for the voltage range (2 V or even 5 V with a divider) at the OP-amps output the offset of an LM324 could still be visible, though not much. One could add an extra trimmer for the offset to an inverting amplifier (works as a summing amplifier anyway).
The meter would likely be OK with the in+ tied to ground and in- as an input, at least for the 200 mV range. This at least works for the ICL7107 in 200 mV range and maybe also 2 V range with a -5 V supply.
I would consider getting one of the cheap ( ~ $8-1) voltmeter units from eaby and test if they can be changed to a 5 V or similar range so that it could also be used for the amps part with a simple extrnal amplifier. Chances are reasonable good, as there should be an input divider to set the 100 V range and the ADC itself is more like 1 V or 2 V.
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See attachment regarding these issues.
A: R41 connected to the wrong wire. It should be connected to U5A pin 2.
B: "stray hair"; unconnected wire or symbol with no wires attached. Remove it or terminate with the "no connection" flag (see icon bar on right).
C: "SW1" appears twice as a symbol reference. One should be SW1A and the other SW1B to signify there are two ganged switches.
D: PWR_FLAG is not a connector. You need a connector symbol here. But don't choose from the Power library (like the +VDC/-VDC from before) as they have Power Input electrical type and demand a PWR_FLAG on the wire.
E: Wire is connecting to the line graphic. It should be connected to the green wire below it, where R12/R11 meet.
F: Delete the wire from junction to VMETER and re-add it. There may be a broken connection along the path.
Also, not identified with a letter is T2 pin 2, loose junction and/or wire. Delete whatever is there and re-Add.
Thanks for pointing all that out. I think I took care of most of it. SW2 has me completely confused. In CC set it shows as 1A and 2B? What am I missing here?
The Rules checker only sees three errors now the rest are warnings.
The errors are "SW1 not annotated" but it is. I even deleted it and put back in no change.
The plug "wall plug earth has been modified in library" error.
The "S+ and ground attached to same items" error by the CC set circuit. If I eliminate the ground I get an warning on U6. @Kleinstein how do I make them all the same as you suggested without causing a problem. Can I just make all s+ grounds?
I corrected lots of warnings by replacing the problem components. Most of the rest (66 of them) are "symbol pin or wire off connection grid' warnings. I redraw the wires and still get the same warnings. Will these warnings cause problems with assigning of footprints or the PCB editor?
I think I am getting real close to having a viable plan for the main board. Though 66 warnings makes me wonder. :) The display section looks like another worthy challenge.
Edit: add drawing
Therm
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With regards to the "S+ and ground attached to same items...".
This is not really an error. It's just telling you which name it will use in the netlist.
In the ERC popup, if you select the error line, mouse right-click, then you can "Change severity to Warning ...".
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With regards to the "S+ and ground attached to same items...".
This is not really an error. It's just telling you which name it will use in the netlist.
In the ERC popup, if you select the error line, mouse right-click, then you can "Change severity to Warning ...".
Thank you
I have posted the original drawing and circled SW1 in both locations. In the current section is shows as S1A and S2B Range is this a mistake? How does the S2 Range switch have anything to do with with this switch? When S1A opens the current Pot adjustment knob becomes active for current ajustment. Am I not comprehending something here?
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You are mixing up some annotation.
S2 A and B change the range of the supply:
S2A lower left the transformer tapping, and S2B the max. possible current range.
S1A has nothing to do with it, because it is just for SET/ACTUAL current flowing.
So the pot belonging to S2B ist 0.2...100% of the current range.
the "100%" == full clockwise changes with the S2B setting.
100% is 2A in the low amperage (= higher voltage) and 3A (= 8V) range:
I hope now it more clear to you
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@andrewtaylor Thank you.
@pqass I went back through to find where you had posted a sequence I should follow and re-read it. So the drawing I think is pretty much done. Its possible I still find errors but I think I'm good.
I realized I was out of sequence when I ran the electrical rules checker first. So I ran the annotation tool and it found the sw1 problem. Then I re-ran the rules checker and the problem was gone. I also made the ground error a warning as you suggested.
So now I am ready to run the footprint assignment tool. I still need to add the fan power and control circuit and any mods that may be needed for the display. Should I wait till this is done before starting to assign footprints? I am going to read back through the display discussion likely several times so I can understand it better before my next step forward.
I have been creating some parts list carts at DigiKey and Mouser. I may even need to add in Newark and Texas Instuments to get it all. I am ordering multiples of most everything figuring It won't hurt to have some spares for future experiments and projects.
@Kleinstein you mentioned some TL062 chips. I would like to order some of those as well as the LM358's I already have in my cart. I would like to be able to interchange like pqass suggested by using sockets. My question is there are many different suffixes on them any particular suffix I should choose? Also TL431LP's also have many suffixes I am guessing the TO-92 package does the suffix matter?
Thanks
Therm
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The suffixes with the TL062 are mainly for the case and temperature range. For a DIY unit the temperature range should not matter that much. I mentioned it, as a near 1:1 replcement for old obsolete LF442, not because it is an expecially good performance, more a cheap easy to get part.
The Tl431 versions have different TC limits. For the first test likely not an issue. For the PCB the details don't matter - the pinout is usually the same. It is a bit odd that Kicad has often so many essentially identical variants.
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The suffixes with the TL062 are mainly for the case and temperature range. For a DIY unit the temperature range should not matter that much. I mentioned it, as a near 1:1 replcement for old obsolete LF442, not because it is an expecially good performance, more a cheap easy to get part.
The Tl431 versions have different TC limits. For the first test likely not an issue. For the PCB the details don't matter - the pinout is usually the same. It is a bit odd that Kicad has often so many essentially identical variants.
Thank you
Therm
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The parts list shows the Front panel pots as a 50k 10-turn ww for volt adjust. That one I found a Bourns for at Mouser. The other for the current side it shows a 10k 10-turn CERMET. That one I cannot find. Is there something special about the CERMET that makes it better for current? Any idea of where I may find one? My net search only finds 1-turn panel mount CERMETs and the 10-turn are all ww.
Thanks
Therm
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So now I am ready to run the footprint assignment tool. I still need to add the fan power and control circuit and any mods that may be needed for the display. Should I wait till this is done before starting to assign footprints? I am going to read back through the display discussion likely several times so I can understand it better before my next step forward.
I have been creating some parts list carts at DigiKey and Mouser. I may even need to add in Newark and Texas Instuments to get it all. I am ordering multiples of most everything figuring It won't hurt to have some spares for future experiments and projects.
@Kleinstein you mentioned some TL062 chips. I would like to order some of those as well as the LM358's I already have in my cart. I would like to be able to interchange like pqass suggested by using sockets. My question is there are many different suffixes on them any particular suffix I should choose? Also TL431LP's also have many suffixes I am guessing the TO-92 package does the suffix matter?
WRT S2A and B (on HPs schematic): The switch to change transformer taps is ganged to to the switch in the CREF generation section. Why? Because if you double the output voltage possible you are only allowed that at half the current; as you're limited by the VA of the transformer. The "S1A" label on a contact of the S2B switch is just nuts. The (momentary) switch called CC SET is just to choose your set vs. actual current shown on the display. I don't know why they called it S1A when there is no B in sight.
You can assign footprints anytime (once you annotate everything the first time). Just save it in the Assign Footprints popup. If you don't delete the symbol, your choice will remain there. You can then add more symbols, then annotate the new ones in the Assign Footprints popup again (previous assignments should remain). Just use generic footprints DIP (double and single op amp layouts) and you'll have lots of op amps to choose from.
The parts list shows the Front panel pots as a 50k 10-turn ww for volt adjust. That one I found a Bourns for at Mouser. The other for the current side it shows a 10k 10-turn CERMET. That one I cannot find. Is there something special about the CERMET that makes it better for current? Any idea of where I may find one? My net search only finds 1-turn panel mount CERMETs and the 10-turn are all ww.
I wouldn't worry too much about exotic pots or 1% odd-ball value resistors just yet. I think you should prototype the bare minimum circuit on a breadboard or perfboard, with a single darlington, jelly-bean single-turn pots, and a collection of op amps to try would be enough to get basic voltage regulation working. You could then add the Current Error Amp, CV/CC Indicators, and then the meters last. At each checkpoint, you'll be testing and gaining knowledge. Then finally update the parts piecemeal to their final form (eg. better transformer, parallel darlingtons, 10T pots, posts, etc.). Your implementation won't be exactly like the version in the service manual.
Once the prototype validates your specific design, you can update the schematic and produce a PCB layout that you know will work. PCB layout without prototyping guarantees that there will be multiple errors that bodge wires can't fix. It's a recipe for frustration.
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I am not aware of a 10T panel mount cermet pot. Both of the pots on my E3612A feel the same in use and appear to be WW. The advantage of cermet is usually over carbon, ie lower TC.
enut11
"Cermet – Ceramic based materials exhibit a high degree of stability over a wide temperature range. Resistive elements that incorporate Cermet inks will typically have very low temperature coefficients as compared to other resistive materials. This characteristic is important for any application that has to operate in a wide temperature range. Cermet potentiometers are very stable and typically have a TC that is expressed PPM. The TC for a typical Cermet potentiometer is 150 ppm/°C (0.015%) which is significantly below Conductive Plastic or Carbon"
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See attached for a photo of the 10T pots from my E3611A. They are Bourns 3590S-A17-503 (-103) (https://www.digikey.com/en/products/filter/rotary-potentiometers-rheostats/84?s=N4IgjCBcodIMZQGYEMA2BnApgGhAeygG0QAmAZgA4AGMAVhAF08AHAFyhAGU2AnASwB2AcxABfMXlLEQ5OgE5qGJngBsUUPwAmnALRhaIVh0ggjINgE8WWTigyIJQA).
I can't find the A17 variant anywhere. It might be the code for metal bushing and metal D shaft.
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WRT S2A and B (on HPs schematic): The switch to change transformer taps is ganged to to the switch in the CREF generation section. Why? Because if you double the output voltage possible you are only allowed that at half the current; as you're limited by the VA of the transformer. The "S1A" label on a contact of the S2B switch is just nuts. The (momentary) switch called CC SET is just to choose your set vs. actual current shown on the display. I don't know why they called it S1A when there is no B in sight.
You can assign footprints anytime (once you annotate everything the first time). Just save it in the Assign Footprints popup. If you don't delete the symbol, your choice will remain there. You can then add more symbols, then annotate the new ones in the Assign Footprints popup again (previous assignments should remain). Just use generic footprints DIP (double and single op amp layouts) and you'll have lots of op amps to choose from.
Thanks.
That S2B was messing with me.:)
Its good to know I can start assigning footprints while waiting on parts.
I wouldn't worry too much about exotic pots or 1% odd-ball value resistors just yet. I think you should prototype the bare minimum circuit on a breadboard or perfboard, with a single darlington, jelly-bean single-turn pots, and a collection of op amps to try would be enough to get basic voltage regulation working. You could then add the Current Error Amp, CV/CC Indicators, and then the meters last. At each checkpoint, you'll be testing and gaining knowledge. Then finally update the parts piecemeal to their final form (eg. better transformer, parallel darlingtons, 10T pots, posts, etc.). Your implementation won't be exactly like the version in the service manual.
Once the prototype validates your specific design, you can update the schematic and produce a PCB layout that you know will work. PCB layout without prototyping guarantees that there will be multiple errors that bodge wires can't fix. It's a recipe for frustration.
I finally concluded after thinking about it I would order parts and start testing (excited to start) before I committed to a PCB design. It makes perfect sense to test first. I was putting the horse before the cart in my excitement.
Thanks for all the advice and help. I am grateful and thankful for you and all the others here who have helped me with this. I am having fun and learning a bunch.
See attached for a photo of the 10T pots from my E3611A. They are Bourns 3590S-A17-503 (-103).
I can't find the A17 variant anywhere. It might be the code for metal bushing and metal D shaft.
Thanks that's great to have that number. I just checked my cart at Mouser and just yesterday I put the 503 50k and 103 10 k in my cart (you must have been putting out vibes :) ). I was doubting them but not since you posted that pic of them. I searched Bourns for the A-17 and it said it was a non standard item. Maybe HP special ordered it. I will also add a couple of inexpensive 1 turns for testing.
Therm
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I am not aware of a 10T panel mount cermet pot. Both of the pots on my E3612A feel the same in use and appear to be WW. The advantage of cermet is usually over carbon, ie lower TC.
enut11
"Cermet – Ceramic based materials exhibit a high degree of stability over a wide temperature range. Resistive elements that incorporate Cermet inks will typically have very low temperature coefficients as compared to other resistive materials. This characteristic is important for any application that has to operate in a wide temperature range. Cermet potentiometers are very stable and typically have a TC that is expressed PPM. The TC for a typical Cermet potentiometer is 150 ppm/°C (0.015%) which is significantly below Conductive Plastic or Carbon"
Interesting, Thanks for the info. I am learning the same value components can be very different depending on materials and construction. So much to know.
Therm
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Would this meter work? You can even program a custom setting if you can't use one of the presets. They Cost $72.00 but look pretty nice. They are 12-24 ac/dc supply power. But should not be hard to provide. Or are these something different entirely?
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For metering I would go for something more in keeping with the LED display on the original E3610A.
You can buy 4 digit panel meters showing both voltage and current for just a few dollars on eBay and similar sites, and they are usually fairly accurate.
[attachimg=1]
For example:
https://www.ebay.com/itm/335327568961 (https://www.ebay.com/itm/335327568961)
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For metering I would go for something more in keeping with the LED display on the original E3610A.
You can buy 4 digit panel meters showing both voltage and current for just a few dollars on eBay and similar sites, and they are usually fairly accurate.
(Attachment Link)
For example:
https://www.ebay.com/itm/335327568961 (https://www.ebay.com/itm/335327568961)
Thanks, I saw those but could find no wiring diagram or specifications on them and with no info its kind of hard to know what I am buying. I like the style though.
Therm
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Most such meters work with a supply voltage anywhere between 4 and 28 volts. Power consumption is typically around 20mA and accuracy is within a percent or better - there are usually two trimmer potentiometers on the back for fine adjustment.
They are cheap and versatile enough that I generally keep one or two in my parts stock.
There are a number of different styles, but they generally use the same wiring scheme. There are two plugs on the back:
- Three thin wires, usually black, red and yellow. Black and red are the power for the meter, and yellow is the voltage sense wire.
- Two thick wires, usually black and red. These are the current sense wires and go to a shunt resistor on the meter PCB.
There's a description and diagrams here of how to wire a similar meter:
https://protosupplies.com/product/dual-display-0-100v-0-10a-panel-meter/ (https://protosupplies.com/product/dual-display-0-100v-0-10a-panel-meter/)
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Would this meter work? You can even program a custom setting if you can't use one of the presets. They Cost $72.00 but look pretty nice. They are 12-24 ac/dc supply power. But should not be hard to provide. Or are these something different entirely?
Not my style but more importantly I find it very handy to be able to resolve mV and mA with a power supply. Great for testing zener diode breakdown and optimum LED operating current and more. This means 5 full digits (99999) for the voltmeter and 4 digits (9999) for the ammeter. These are a little more expensive but tend to be more accurate.
This voltmeter is about $14AUD delivered. eBay item number:335203244430
enut11
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Most such meters work with a supply voltage anywhere between 4 and 28 volts. Power consumption is typically around 20mA and accuracy is within a percent or better - there are usually two trimmer potentiometers on the back for fine adjustment.
They are cheap and versatile enough that I generally keep one or two in my parts stock.
There are a number of different styles, but they generally use the same wiring scheme. There are two plugs on the back:
- Three thin wires, usually black, red and yellow. Black and red are the power for the meter, and yellow is the voltage sense wire.
- Two thick wires, usually black and red. These are the current sense wires and go to a shunt resistor on the meter PCB.
There's a description and diagrams here of how to wire a similar meter:
https://protosupplies.com/product/dual-display-0-100v-0-10a-panel-meter/ (https://protosupplies.com/product/dual-display-0-100v-0-10a-panel-meter/)
From my experience, the 4 digit types have very accurate current measurement because they have chopper auto zeroing.
The big annoyance is the refresh being slower than the usually advertised 3 times per second. It can actually be once per 2 seconds.
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The very cheap 3 and 4 digit modules may use a µC internal ADC and oversampling to get just enough resolution. This can result in a rather noisy or slow update. I have seen less of the 5 digit modules lately - a few years ago there was a teardown shwoing a microchip 18 bit SD ADC inside, suggesting 3-4 samples per second if no extra oversampling is used.
The instructions are often a bit vague on how to connect. At least they usually show if separate wires for the supply are used. Given the low price it may be worth getting a unit upfront and experiment with the interface.
For the current reading the shunt on the module can complicate things a bit. It may be easier to use votlage reading modules and amplify the shunt voltage if needed.
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Those meters are pretty cheap I will order some just to experiment with. At minimum I will learn something. I can wait a couple of weeks for them.
The Trumeter has my interest because of the True RMS or peak feature. I was wondering if maybe they would solve a lot of the configuration issues caused by the cheaper meters?
I should be placing an order with both Digi and Mouser this week. They had most of what I need. I will still need to go back and read this thread again before sending the order. To make sure I have all the alternatives covered. I have over ordered to be sure I have some extras in case some of the smoke escapes on the cheaper stuff. Plus to have some different op-amps to try.
In the meantime I have some components to start to experiment with. Transistors, regulators, op-amps misc stuff I have laying around. I need to get back in the groove after 40-50 years on the bench. :) I have been using a 12 volt 2 amp supply from my old DSL modem i converted. I run it through a ltm8067 DC to DC converter. It works for now.
Thanks
Therm
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The output of the supply is DC. So no need for true RMS and hardly any need peak detection.
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The output of the supply is DC. So no need for true RMS and hardly any need peak detection.
I did not know True RMS was only for AC power. I had to look it up makes perfect sense.
Is there any advantage to using toroidal T-former I saw a build where one was used? Pros, cons?
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I had to switch to a toroidal transformer because the leakage flux from the EI type I originally used caused the display on my DSO to wobble.
It's classed as medical grade, I think due to it having electrostatic shielding.
https://www.eevblog.com/forum/projects/linear-lab-power-supply/msg2388873/#msg2388873 (https://www.eevblog.com/forum/projects/linear-lab-power-supply/msg2388873/#msg2388873)
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Toroidial transformers have pros and cons: on the pluse side they are more compact / lower weight, lower magnetic leakage and usually better efficiency. As down sides they may not have as good an isolation (not 2 really separate chambers), a bit more tricky to mount and have a larger turn on current spike (may need extra circuit beyond some 150 VA). The lower output resistance has pros and cons (less voltage sag under load, but larger current spikes for the rectifier).
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I had to switch to a toroidal transformer because the leakage flux from the EI type I originally used caused the display on my DSO to wobble.
It's classed as medical grade, I think due to it having electrostatic shielding.
https://www.eevblog.com/forum/projects/linear-lab-power-supply/msg2388873/#msg2388873 (https://www.eevblog.com/forum/projects/linear-lab-power-supply/msg2388873/#msg2388873)
Nice work on that.
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@andrewtaylor recommended I use a dual 12v 4a secondary T-former for the primary power. I found the one attached.
Is this the correct dual secondary transformer config?
I assume I will be switching between these windings for High and Low range is that correct?
The one thing that puzzles me is the 117/234 VAC primary? Does it matter that its not 115/230?
I have not yet found a dual 15v 200 ma for the Reference/Bias supply yet. Any advice on finding one?
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For the regulator supply one should get away with less than +-12 V DC as in the HP schematics. Some +-8 V (so that a 5 V ref is OK) should be enough.
So one could get away with less than 15 V AC for the transformer, maybe only 2 x 12 V.
For the main transformer rating one has to keep in mind that 1 A DC from rectifier and filter cap needs about 1.6 A of RMS AC current from the transformer. So the 2 A rated transformer would be good for some 1.2 A of DC output with the higher voltage.
The exact voltage for the primary is not that relevant. The 117V winding would be perfectly fine with 110 V or 100 V, just the secondary scales down accordingly too. So not 24 V but more like 22.5 V at nominal load. A transformer is fine with lower voltage - just with a lower power rating as the maximum current still stay the same.
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I am seeing T2 as a center tap transformer. So, I think I would need a 14v or 16v secondary winding with each side of center being 7 or 8 v? Or is my thinking flawed?
And with T1 I am seeing a 2x?v winding wired in parallel with 3 common, 4 high range winding and 5 low range winding. Am thinking correct or am I wrong and misunderstanding something?
I have placed my orders and I should have all the components I need early next week to begin testing on the breadboard. Though the display will be another week. I guess its on a slow boat from China. :)
Thanks
Therm
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To get a +-12 V auxiliary supply for the regulator one would need a transformer with something like 2x14 V - 16 V.
Just 16 V with a center tap or 2x8 V would not be enough for the +-12 V like in the HP plan. It could still work with some +-6 V for the regulator part. This should still be enough though it could be tight with a 5 V reference. There is not real need to have +-12 V for the OP-amps. They are perfectly OK with less.
A lower voltage could be a thing if the voltmeters are power from the same supply.
As shown T1 also has a center taped winding and is using only part of the winding for the high current - so no parallel connection. This way the permissible current at the lower voltage setting is usually not all the way 2 x , but a little less (e.g. 1.6 x). There is not easy, unviersal ratio as there is loss from the primay and secondary and the local vs global loss question.
Ideally there are 2 completely separate windings in parallel for higher current or in series for the higher voltage. However this would need a less common 3 (or 4) pole switch to also have poles to switch the max voltage/current.
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To get a +-12 V auxiliary supply for the regulator one would need a transformer with something like 2x14 V - 16 V.
Just 16 V with a center tap or 2x8 V would not be enough for the +-12 V like in the HP plan. It could still work with some +-6 V for the regulator part. This should still be enough though it could be tight with a 5 V reference. There is not real need to have +-12 V for the OP-amps. They are perfectly OK with less.
A lower voltage could be a thing if the voltmeters are power from the same supply.
So would a 2x14v be producing 28v since the center tap is grounded and the bridge is being fed by the outsides?
As shown T1 also has a center taped winding and is using only part of the winding for the high current - so no parallel connection. This way the permissible current at the lower voltage setting is usually not all the way 2 x , but a little less (e.g. 1.6 x). There is not easy, unviersal ratio as there is loss from the primay and secondary and the local vs global loss question.
Ideally there are 2 completely separate windings in parallel for higher current or in series for the higher voltage. However this would need a less common 3 (or 4) pole switch to also have poles to switch the max voltage/current.
Regarding T1, so when the switch is set to high it has one 12v higher amp output? Then when switched to Low it now has a 24v lower amp output? Is this correct?
Sorry if these are dumb questions.
Thanks
Therm
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A 2x14 V transformer with the center tap at ground would give about +-18 V at the filter capacitors. With a small transformer and low load the voltage can be some 20 % higher. So about OK (with plenty of reserve for a lower mains) for the +-12 V regulators.
For T1 one one would have to choice of something like 24 V / 2 A or 12 V up to about 3.2 A DC (assuming a transformer rated for some 3.3 A AC).
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A 2x14 V transformer with the center tap at ground would give about +-18 V at the filter capacitors. With a small transformer and low load the voltage can be some 20 % higher. So about OK (with plenty of reserve for a lower mains) for the +-12 V regulators.
For T1 one one would have to choice of something like 24 V / 2 A or 12 V up to about 3.2 A DC (assuming a transformer rated for some 3.3 A AC).
Thanks for clarifying, I understand it better now. andrewtaylor and his original advice was actually pretty good. Now with your help I fully understand why it was good advice.
Thanks
Therm
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I had several questions I was going to ask and decided to re-read the whole thread from the beginning first. All my questions had already been answered, I just did not absorb it. Some were answered twice. :) I don't know if it were info overload or just reading to fast. This thread is a great reference for me. By re-reading I did come up with a new question though see the quoted post below.
If you will be testing the design on a breadboard, consider connecting R6 to the ORing node instead of directly to the output of the CV opamp. This idea suggested to me by Kleinstein greatly reduced the voltage overshoot in my PSU design whenever it transitioned from CC to CV mode.
What does this mean? What is the ORing node xavier60 is referring to?
I received a box of components from Mouser yesterday (Sat). I have another due from DigiKey tomorrow (Mon). I will be able to begin mocking up the circuit on the breadboard. I am going to take pqass's advice and work in sections getting each section working before moving on to the next. Rather than just building the whole thing from the start. I ordered the display posted by rolycat. It should be here late this week or early next week. I chose that one because it had both amps and volts. We shall see if it can work, it is cheap enough to experiment with.
I am still pretty much dedicated to the original HP design. Although some changes seem likely for the display to work properly. As this project has progressed I have become a bit more open to some design changes based on testing. But as of now I plan on sticking to the plan.
Thanks to all for your help so far. with a special mention to pqass and Kleinstein.
Therm
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During initial testing, the values of R6 and C6 might need to be altered if the CV regulation shows signs of instability.
Another test involves momentarily overloading the PSU's output while monitoring the output for voltage overshoot during the CC to CV transition. At this stage, connection of R6 can be moved from the CV opamp's output to the anodes of CR4 and CR5 to see if there is a worthwhile reduction in overshoot.
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Thanks @xavier60
I have another (maybe dumb) question about mounting the heat sinks.
I thought in the past I just mounted V regulators with thermal paste to the heat sink. But a TO-3 transistor I remembered had a mica insulator sheet. I noticed at the suppliers they have mounting kits with either mica or thermal pads for the TO-220 and some others.
Do the Darlingtons (TIP142) need an insulator or is thermal paste sufficient? Also whats needed for 7805, 7812, 7912 V regs?
I will be mounting heat sinks on the diode bridges also, anything needed with them?
My DigiKey order arrived early (yesterday) so I am ready to start. I want to be sure I don't get ahead of myself and make stupid mistakes.
Thanks
Therm
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With TO3 and essentially all TO220 transistors the case metal is connected to the collector of the transistor. If one needs isolation depends. Thermal past alone is not a vaild isolation.
For the 7812/7912/7805 it depends on the power loss if and how much heat sink is needed. With a low consumption for the regulator part there is a chance to get away without. One could still reserve space for a small heat sink. I would consider some 200 mW OK for a 78xx without a heat sink, so maybe 10 V and 20 mA. Chances are the LED display would need more power.
The diode bridges for the auxiliary power likely can get away without a heat sink.
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With TO3 and essentially all TO220 transistors the case metal is connected to the collector of the transistor. If one needs isolation depends. Thermal past alone is not a vaild isolation.
For the 7812/7912/7805 it depends on the power loss if and how much heat sink is needed. With a low consumption for the regulator part there is a chance to get away without. One could still reserve space for a small heat sink. I would consider some 200 mW OK for a 78xx without a heat sink, so maybe 10 V and 20 mA. Chances are the LED display would need more power.
The diode bridges for the auxiliary power likely can get away without a heat sink.
The TIP142 is actually a TO-247 I mis-quoted that. But I would assume the same is true for that package. What would the need for isolation depend on? Would providing such isolation as a precaution have any negative effects if it were not needed?
I am going to provide heat sinks for the regulators if for no other reason that the pictures I have seen inside of the power supply have all had them.
Thanks
Therm.
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Insulators add thermal resistance, which means the junction temperature of the transistor (Tj) will be hotter. Hotter means less reliability, or lower current supply capability for the same level of reliability.
In linear power supplies, you try and avoid the need for insulators where you can, but sometimes you can't, or you are not using the transistor near its limits, so the extra thermal resistance does not matter.
In high current linear power supplies, this can be a problem, and you can actually regulate the negative rail, so the pass transistor collector is at GND potential. This is what I did for my 50 Amp 13.8v supply.
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Listen to Kleinstein
As far as I know almost all transistor packages have the collector or drain connected to the tab or the metal on the back of the package. This needs to be electrically isolated from the Gnd. I think your are building an Isolated PS with pos and neg terminals. These are not referenced to Gnd (until you want them to be). I think Mica is the best along with heat sink compound. Silicone pad is also used. The Tab or back of the package needs to be thermally attached to the heat sink which is almost always grounded. It needs to be electrically isolated from the Gnd. The metal screw that attaches the transistor to the heat sink is also electrically isolated, sometimes this screw is a non conductive Nylon screw. Heat sink compound helps the thermal conduction by establishing a better thermal connection, filling in most mechanical deformities. It will not electrically isolate the transistor by itself,
There are a few RF transistors that I am aware of that the Emitter is attached to the Tab, this is unusual and there is no electrical isolation used with these transistors, but heat sink compound is used without the Mica. I am not aware of any Power Transistors that are configured this way.
This goes for ALL flat packages and also the metal can of the TO3 transistors (and other can transistor size)
Sometimes when the transistor or volt regulator IC does not handle much power the transistor is left "flying" or unattached to heat sink. Not very often though.
I think it is safer to heat sink all the devices that are designed for heat sinking, Even if they can work OK without sinking, they will have better heat stability with heat sinking. There are little metal heat sinks that can just be attached to the back of flat packages that are not grounded and can help a lot also. Heat or rather temp change is a big enemy of stability is any PS.
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Small heat sinks don't really take more heat away than the device pins, unless they are in thermal contact with the board. Some of those small heat sinks are meant to be soldered into the board. One can also put larger copper pads next to the power transistor to help spreading the heat into the board. Sometimes those pads are kept free in the solder mask in order to cover them with solder, once more reducing heat resistance.
Another method is mounting power transistors flat on the board and soldering them onto a cooling pad like SMD parts.
Regards, Dieter
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This is a pic of the inside of a 361X I scrounged off of the net. The voltage regulators seem to have oversized heat sinks soldered in. The Darlingtons are the TO-3's mounted to the rear cast alum heat sink. When looking close they all seem to have mica insulation, but it is hard to tell. The TO-3's are obsolete and I am using a TO-247 package. It would be difficult to try replicate the large alum casting so I am experimenting with using two fan cooled large heat sinks with one TIP142 Transistor mounted on each one. They mount back to back and share a cooling fan.
enut11 posted a very simple but nice thermistor controlled on off fan switch but I worry about temp swing using an on/off type. I think I found a relatively simple variable fan circuit that is thermistor based and may help to keep a stable temp. I don't know till I try. Or I may just go with full time fan on and be done with it. :) I wanted to build something difficult and this definitely fits the bill so far.
I appreciate any and all advice, thanks to all.
Therm
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You can probably mount each of the TO 247 using the screw holes of the TO 3 transistors. Most of the back of the TO 247 should be in contact with the heat sink using the insulating mica and compound. You can probably use the existing screw and nut you have since the 247 does not require insulating the screw.
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enut11 posted a very simple but nice thermistor controlled on off fan switch but I worry about temp swing using an on/off type. I think I found a relatively simple variable fan circuit that is thermistor based and may help to keep a stable temp. I don't know till I try. Or I may just go with full time fan on and be done with it. :) I wanted to build something difficult and this definitely fits the bill so far.
Therm
Hi Therm
That 2 transistor fan controller from Reply #76 is a variable fan speed control. Ie, the hotter the heat-sink the faster the fan will spin. As the temperature rises the thermistor resistance drops which allows more base drive current for the transistors. The pot is just for adjusting the threshhold temperature. This could be around 35-40C, but your choice.
enut11
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Hi Therm
That 2 transistor fan controller from Reply #76 is a variable fan speed control. Ie, the hotter the heat-sink the faster the fan will spin. As the temperature rises the thermistor resistance drops which allows more base drive current for the transistors. The pot is just for adjusting the threshhold temperature. This could be around 35-40C, but your choice.
enut11
I did not catch that. I will give it a try it is a very nice simple circuit.
Thanks
Therm
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This came in today and gave me a good chuckle. I had no idea how small it was. But rolycat was correct about being it being pretty accurate. I hooked it up to my ham radio 12v power supply and it read 14.02 v. I hooked my Fluke 87 to the same supply and it said 14.01 V. Pretty close for a China cheapie. :)
I have not started mock up yet because the heatsink for the Darlingtons did not come with the cam clips needed for attaching them. So I had to order some and now I'm just waiting again. I did get to attach the fan and test that it works so I guess that is progress. I plan to monitor the case temp with my infrared thermometer to see if it will be able to reject enough heat. We shall see.
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With those panel meters, I have never been able to make use of the 4 retaining tabs because they never want to spring in for me. I have been breaking them off and relying on a neat cutout in the front panel.
I'm curious about how the display refresh compares to the advertised specs.
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Hi Therm,
Did any documentation come with the meter?
It would be helpful if you can provide a closeup of the backside.
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Hi Therm,
Did any documentation come with the meter?
It would be helpful if you can provide a closeup of the backside.
Absolutely zero documentation. The only reason I knew how to hook it up was the markings on the board and rolycats post. I can't figure what that push button in the center does? It is tiny, but since I have it I may as well experiment with it. Pic attached. Best I could do.
Thanks
Therm
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The two issues I identified with these cheap meters in my reply#36 were their burden voltage, and (on some meters) that you couldn't dial-down your PS below a minimum voltage (4.5V) without starving the meter for power. Fortunately, the burden voltage from the meters built-in (low-side) shunt can be removed by attaching the wiper and lower fixed contact of (10T) pot R37 to point B (vs. A) in the attached diagram (from rolycats link (https://protosupplies.com/product/dual-display-0-100v-0-10a-panel-meter/)). And by providing the meter with its own FULLY ISOLATED supply, it will happily read 0V with R37 fully CCW.
Having two shunts in the circuit does introduce another voltage drop (probably by a few 100mAs) between unregulated to regulated sides, however, I think the simplicity of the meter installation makes up for that; ie. NOT having to configure the meter to use your existing shunt (R2), choosing a full-scale Vref, calculating dividers, and re-calibrating. And the bonus of eliminating R11, R12, R18, and R17. UNFORTUNATELY, by using this meter (with built-in shunt) you won't be able to set/view your current setting by pushing momentary SW1A. Instead, you'll have to short the outputs while adjusting R19.
These cheap Chinese meters are not based on the custom logic ICL7107 ADC but instead on a cheap ($1) STM8 MCU (https://www.st.com/resource/en/datasheet/stm8s903k3.pdf) with 10bit ADC. It probably uses oversampling (https://ww1.microchip.com/downloads/en/appnotes/doc8003.pdf) to get 4 extra bits to achieve 10,000 counts (at 2 Hz refresh).
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The two issues I identified with these cheap meters in my reply#36 were their burden voltage, and (on some meters) that you couldn't dial-down your PS below a minimum voltage (4.5V) without starving the meter for power. Fortunately, the burden voltage from the meters built-in (low-side) shunt can be removed by attaching the wiper and lower fixed contact of (10T) pot R37 to point B (vs. A) in the attached diagram (from rolycats link (https://protosupplies.com/product/dual-display-0-100v-0-10a-panel-meter/)). And by providing the meter with its own FULLY ISOLATED supply, it will happily read 0V with R37 fully CCW.
Having two shunts in the circuit does introduce another voltage drop (probably by a few 100mAs) between unregulated to regulated sides, however, I think the simplicity of the meter installation makes up for that; ie. NOT having to configure the meter to use your existing shunt (R2), choosing a full-scale Vref, calculating dividers, and re-calibrating. And the bonus of eliminating R11, R12, R18, and R17. UNFORTUNATELY, by using this meter (with built-in shunt) you won't be able to set/view your current setting by pushing momentary SW1A. Instead, you'll have to short the outputs while adjusting R19.
These cheap Chinese meters are not based on the custom logic ICL7107 ADC but instead on a cheap ($1) STM8 MCU (https://www.st.com/resource/en/datasheet/stm8s903k3.pdf) with 10bit ADC. It probably uses oversampling (https://ww1.microchip.com/downloads/en/appnotes/doc8003.pdf) to get 4 extra bits to achieve 10,000 counts (at 2 Hz refresh).
After seeing the size I am not likely to use this meter for my project. It will be ok to experiment with a bit but it's just too small for my liking. After hearing your assessment of it and now knowing the CC switch wont work. Well that kind of seals the deal for me or the no deal anyway. It is an interesting little meter though. I bought it just to have something to use till I made a final decision. But did so with an open mind in case I really liked it.
I tested it again against the Fluke and they are both the same. I just needed to be sure the little test clips were seated properly. Here are Pics of dual power supply wiring style, both Amps and Volts. The load is the Heatsink fan. I am amazed at the accuracy of this cheap little meter. The amps fluctuated but both meters stayed together.
Thanks
Therm
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I have received everything I need and have begun to mock up the circuit. I have started with the main power circuit trying to get it working before I then proceed to the Ref and Bias section. I am using a 12 volt 2a switching supply as the main power source. Bypassing the new t-former and bridge for now. The 12v + and - that should come from the ref supply I am using my 30a 12v linear Ham Radio power supply for now. I did not want to use it as the main supply because its 30 amps and I was worried I might hit those Darlingtons with 30 amps by mistake if I wired something wrong.
I cannot get it to put out a voltage so I can't even try to see if its variable. I am using only one Darlington it has 12+ on pin two (C) from the supply and 12- on pin one (B) from the 2N4036. But it has no output on pin three (E). All 12v+ and 12v- points are powered from the Ham supply. The heatsink fan is also on the 30a supply and all S+ points are joined at the end of + output rail after TP3.
I did not land 5V ref, is that maybe my problem? Or am I just doing this completely wrong? If it is the 5v Ref that is the problem, can I just power the 5 v regulator off the 30 amp supply?
On the attached Schematic only the section in red is completely mocked up.
Thanks in advance
Therm
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I am using a 12 volt 2a switching supply as the main power source. ...
The 12v + and - that should come from the ref supply I am using my 30a 12v linear Ham Radio power supply for now. ...
I cannot get it to put out a voltage so I can't even try to see if its variable. I am using only one Darlington it has 12+ on pin two (C) from the supply and 12- on pin one (B) from the 2N4036. But it has no output on pin three (E). All 12v+ and 12v- points are powered from the Ham supply. The heatsink fan is also on the 30a supply and all S+ points are joined at the end of + output rail after TP3.
I did not land 5V ref, is that maybe my problem? Or am I just doing this completely wrong? If it is the 5v Ref that is the problem, can I just power the 5 v regulator off the 30 amp supply?
On the attached Schematic only the section in red is completely mocked up.
You need to create a ref supply (your 30A ham supply as described) of +12V, -12V, and +5VREF, whose GND (as stated) MUST be connected to +S/+OUTPUT. If you don't have the TL431s, you can use a 7805 or equivalent means to generate +5V from the +12V. This supply must be ISOLATED; ie. its GND MUST NOT be attached to PE (3rd pin on mains plug). EDIT: If this isn't possible, then the other (2A) supply (output posts) must be isolated from PE.
Seeing -12 on the base of the darlington means that it is OFF due to Q2 being ON. Q2 is ON because U1 output is -12V because -V (pin 2) is higher than +V (pin 3) being pulled to -OUTPUT via R37. You need +5VREF to pull up on the upper half of the R15+R37 divider.
ADDITIONALLY:
See attached for minimum required components for voltage regulation. Simulation here (http://www.falstad.com/circuit/circuitjs.html?ctz=CQAgjCAMB0l3BWcMBMcUHYMGZIA4UA2ATmIxAUgoqoQFMBaMMAKAEMRCFCRs0KUeXv2LgUIJuLDx4UCTBmQwGPJBQpiynMQAseEjuQyWAExB6qfWoOFVxJugDM2AVwA2AFxYAnc6tvmYDxWctJwLB6BwfzYhEIhVExi0DqQxAjcmngIGMTq5AwwXCg6XIRwYNk6uTxhIA7O7l6plnHgGDw6fO21UAA6AM5ggwwI0MSQpak5GRgIOsMDMNVgfIRgxHzYqihBg2GDDa6e-UMjhNDYc8SEhB14eKtdKIMwCBMkhHwZRHEIePs4IcnMdIqwAEq8NrYWJQ+J4QxUKipCRgcRIqDQBCmKLmOC4kL2EFNFgAc1xLQpQTkkBYAHc4bxJoySkj6SyUbEhMoeLSAG4gVl+OwosA6RFyUXomlY9lCsWGZ7gcVQdlKhXmbpBNkMoUWEA4Tr+Wm+fUhfVC5EYcK+LmClEWlFUNHhSGO5H+NBCDFSmmY7EM9V5EB4LXB2nk0NSYNRwUlGns2MbcSaaPo9mG4UgVNZk3ZtHgYM5-XO4wAByM3ODYSEZoTDJrWeLxvZjeT+bTqvJZV4sJ72AQ0rz1sMuEMI-tGLAlFdBuZQonXr9KKQGLe7P7zInY9VynHsIH4gnU3ANFkRWIqkU14gAGUAKIAFRAADUAPIAGUfAEEAOL3jNmQWHht0HVUGVAo8DzA2kIOZQ851HZlaQrNFuRVNCs2wesxHQwx5RVWDcKzPUWwAD2QFAkA2QxmGwWiyHMe0QD6Ms3wAVUfAAFTiWAo6QqL8bk0VEHRNCY+MGA47jeKAA).
The components from your schematic not represented here are for protection or to slowdown the feedback to keep it from oscillating.
Ref supply of +12,-12,+5V, and their GND is attached to +OUTPUT.
The bulk supply that's being regulated needs to be isolated from the ref supply is represented as a 12V battery.
The R37 pot travel tops out early (3/4 CCW) because R15+R37 is tailored to having a 20V bulk supply.
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@pqass Thank you. I do have some TL431's, I even bought extras. Sometimes I can't the see the trees, for forest gets in the way. ;).
Back to the grindstone
Therm
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I wired the TL431s in series they output 4.99v so I will call that a 5v a reference. Still no output on pin 3 of the TIP142. I even tried swapping power supplies.
The thirty amp does have a PE on the mains and it does have continuity to the negative output. It does not matter if the switch is on or off. So I switched that to the main supply. The 2a switching supply has no ground pin on the plug so I tried that as the reference supply. This made no difference.
There is no GND output on either supply unless you are talking about v- or the black output as GND.
If I use the 30A supply (now primary) Neg terminal for measurements I Get (B) .24v (C) 13.98v (E).2v. If I use the 2a supply (now reference) as neg term for measurements. I get the same reading plus the 4.99v reference. (B) 5.23v (C) 18.97 (E) 4.99.
I even thought maybe I smoked the Darlington because it rang out on diode check pretty weird. I was expecting a normal NPN type reaction. So I checked it against an unused one and they were the same. When I looked up the schematic for the Darlington it made more sense. So now I am wondering if it is some kind of isolation problem? Maybe I need to just mock up the two transformers and bridges too.
I have triple checked my circuit on the breadboard I am pretty confident it is correct. Any ideas? Am I making an isolation error somewhere maybe?
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The "ref" supply NEEDS to be bipolar (have 3 output posts), that is, have +12V, 0V/GND, and -12V outputs.
Measuring DCV between +12V and -12V posts with a multimeter should read +24V.
That GND must be connected to +S/+OUTPUT.
The +5VREF is derived from the +12 as you've done with resistor+2*TL431 to GND (not the -12V post).
The "bulk" supply can be just +12 (to +20V) between 2 output posts (not bipolar).
One of the supplies must be fully isolated from PE; have NO continuity from any output post to PE or the (wide) neutral prong (on a polarized wall plug). The latter shouldn't really exist but check anyway.
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The "ref" supply NEEDS to be bipolar (have 3 output posts), that is, have +12V, 0V/GND, and -12V outputs.
Measuring DCV between +12V and -12V posts with a multimeter should read +24V.
That GND must be connected to +S/+OUTPUT.
My ref transformer is a DP241-5-28 2x14 .400 mA centertap. That will give me my ground for the TL431s, and the fully isolated supply. At least that is what I think will happen. Using the center tap as GND, am I correct?
The +5VREF is derived from the +12 as you've done with resistor+2*TL431 to GND (not the -12V post).
This is good to know because I used -12v for it. I am still not sure how they work to create 5v. But they sure do.
The "bulk" supply can be just +12 (to +20V) between 2 output posts (not bipolar).
One of the supplies must be fully isolated from PE; have NO continuity from any output post to PE or the (wide) neutral prong (on a polarized wall plug). The latter shouldn't really exist but check anyway.
I have the Transformer a 266L24 2x12 and it can be a 2a or 4a depending on using one or two windings selected by the range switch. I understand I can wire it and use it like a center tap. GND the chassis with the PE not the center winding like the REf. Is that correct?
I think I am just going to wire the Transformers and the bridges and at least know my power is correct.
Thanks
Therm
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The "ref" supply NEEDS to be bipolar (have 3 output posts), that is, have +12V, 0V/GND, and -12V outputs.
Measuring DCV between +12V and -12V posts with a multimeter should read +24V.
That GND must be connected to +S/+OUTPUT.
My ref transformer is a DP241-5-28 2x14 .400 mA centertap. That will give me my ground for the TL431s, and the fully isolated supply. At least that is what I think will happen.
Using the center tap as GND, am I correct?
Yes.
See attached (first power supply) and simulation here (http://www.falstad.com/circuit/circuitjs.html?ctz=CQAgjCAMB0l5BOJyWoSATLSAOArHgMwBsCGhYOA7MVSHpPfY3gKYC0YYAUGKSDkYJi4MiGFRwUaHxDsYVahjAIqYPDj5UMBOTmg5NigCwqqcMDowdZ7fYbAmzFqzZEwk3ACaY8IyziYhuIiGCBerABmAIYArgA2AC7eQYEShBiMAZjhUXFJKTr+GIElgXyMYRExCck+ZeDEjBlZJTnV+ckA7qJhEg0SkNwA5r3gbZnlbYxDPSphFamNM9w9ReOlxq2Bs5hbG3uVflCrh74ihHhh67stB5cL0yMgD2N385K3V5JNOycATiBfj9cAIZuB4KdXtlXitTCwaOBLPQxI5-CAAH4AFQAMsYKFAADoAZ32GBJYBs5OJCkIhHwCEcTNofmplRJ1k41Pk2DgeCQOBKhDIFA05gQJJmFJJPPgkH5CEFOGF5HU1EQkugVDpDKZahZxGpYC2JIxiXi+MpXnYAEcAHYAfVYPkgJIygiJxIwWylxO0cE9dOgdJDobDoQp0E5lk12kskC2VA0eDUeFMkswHOgxipMpgcpIVG12mM5mMxiIkGIGddxLAed5kELxe9ZYrhCrseUmUTydT6brJuJZotFGdtsd44AgmAo57KDJNEvKCul5mvVG5Vut4RczToLRlZdGU2tIIcBnqcZs9vb5SuZrIFpzNRSJAyoK0zXpfun7QXzQCDvoYn7GJqh50vyYCnoeuAUkOI6WuO9pOtaU5YGEtaCL6ZIUnuCgJhgwjkIoiCWOol4cvhsDKBojIEOoxAUMYipUN+daPrROD0XgjHMaxsaEcRhCkYytHwbWiFjtaKHOp6Po4eydbUW2+LaMQ0EVEglFenusqKqWabapQBAIFcYE0vODaIDghmlhQ+D8uZgnlmpGAaX+iASoOknmkhMmTi6JIetSbCcIQXaQEmRGGAmUXEMYF6WUaekwIIFbQeWhD4lWireb69bEjy6W8Qm+I5aQ3GRdFirpfFiUSaafnSROqHsFOMB4J6IV4Q+RUEZcKhNgQgrltoOm7n1+bwDgxAaU0T5NgKzmWbWnCPjNc0VItwqKitPLmINQGXBo3qltSTRNaOVq2gADqh3VKfeMb9VqTbGExFDqFccAIBFyVutRGDuUR5ApuQZlJgl7HrfuwOGiK4PCimfgWQd72fVwBCZIg-2XcOzU3Ta91yVhAZk4p67PWyWrKMKZW8aYGgVjp0bch4Rhlk2UNXIo7GFTyiqOFzIl+LzSUKHTQHlozaosz5V3+a1pMUgw3XrmFL0KMq1DKnARYscQBA6c9AuztoX22QgiWlkBGn8zK5uqpQLE21QduFdr9KKB2UVUIbxsKwT13IYF7VdbW0HwPJT2pdAQvanSCXGmolxsQDul9deGBxvSKjUCmTRsw7pJRrnmisYX75xwnIbJ6WYBp41wdK7J9SKy1XgPZH0fUlJN1d3JKWcJ78dGHXTPGlF+XrtGAv5gZrIiVWlAlZK3DwvQiLeiwYgdsYUjYniBK1rhylTVqOpQWo+pqN6rNx3KCpKiqLSWyXsrwM-Qoipk7-7onXUN8tCWAslPDuRNAqBhKL6Hevp-S+iDGGZBdcqZRhUt2OKSZ8AvkMKzbMj94DNhEq2BMigNLuQ-tNOAxCSxlnIZYasADMG9hwbgPBQd+6hzajOOckd9CrkEcuUoWYca3h3NRCCx5oIUANBLdc14FLiIsNRP8RZcCAVPPSa2-0CqPmfBot8FBtH4nAj7aRMEoZJXAS3Fqbd2oYUepTYeWs3rGCIoaES550pslnqoriPFvoZEcIKEu+YAnfSCcoRQNMyweJIt4wizcuEBW7iSBSMcqYqTKm5Dylg-q+OpMXV6Nk7LGVfAwNQVDYAGSTPZSgNBKmj1UiQvJREMjJMJtwlWxIerEk1ro2mUUri1TinNCysc+rFQTKVLKOVZpaysq9EqmVyodgWbEzINVYpbHGZ0kOqTpydUelkqZA1eLHRGls+R1JJquLlLNeaFhho0CYjPNao8HlbQWjIwubyGyHQucNU6UUkr4xSXdNJvTJkvXRtlTGkS5qUIzncmm8NQZp3ILNEUEzPSwxgOixGFtsXkDRgND6dIsa8SRUw8FXSZIkyCtC302FMkuM2Y3aWGVTDzVxUUmunM4qiwrGZT2SzBaCq2MKpyzSpYM2NHwPgYCEL0uVky9QLKNYqR1j7fW-tVAJhNjYM2tNLau1sk0Ds6c9FFSdma62FqmxRVjDqvWfsWJln2a3MOU4I4UjlGy3qsKOaOAnsaH6JQH5ZzLh2dyIkb7anfJrXxkd0kxvfExIswtY3JobLXJOpgKyZEjZw1Vbd1wQsHuq3uEDxxVtOVwTU+aSCFutkmGe-KR7WUXp48wbzsoaHXj0Qu4ByxbxEB6XYI6PTAknacEdOcwgLtBFO7eoJgSTBOKMYEScgSglhCcHorx1ivHpAfL4YQz0gBMC8Wyh691-BvSsW61672MBvR8QgkgeAvo-WIG9V6v1ZGeP6MYoHgbnpOAANzBCEWDiwsh7vAOYT40g8DcBfewCQEgsP+CaC8KQPAei4bgx6QYpwSOLA9Ah7gABjF43wYSMbEDMXkpZlFbgPpYLUypVBmTTLGk+2AeD0ehHvb4NxpDwHYxx6T4BCDBhoFwFijgShZR2MJ04s732ZFg7sUDHw-2YQw9e3THoDN70+NwAAHtepA4gBAaHGCAA+3oQCElupYAAajZuzgRtGOYgCqFzew5Ded8+7dAxaITuUwPKELbnIBeYAPQAHEAByAARZLHmADyABVLEAAFQrvmjZdX9te-E166CuYPh5vAXmABKABRAAYmVkgQQwjEHwEELqXHAi4ktJ1rjuhetfrVCFygIBhsUF8x2dA7BeJAhYnIRKCWD4AEkADKuWcRTixC1zLJJWttZJEV3LAB1FrTWSQ7fy0VorOIACaC2cMDc0L4TbIAcQAFlFAxkJHaEkJIAASt2WvvfQPSRgNsXPQR+-992QOQfEnB5D545Z-PfGxy8XTKxRh44yC5jbCUrO7Lg7xa4bnqffukMgcAAAuWAOAAA0rOCMHSUGYNUfBbLfE-hYL6cAc6aW9PgbKUn4CNy4KLtQQ1yLvhABvIiLwEz0DHVetMkGIAxHiMSVgmBTgQc1wffeZv72m78M0DXNv70W-5JejXCUVhHpd-sHlq23e3oPiO-ES7ES7AD+OlzJO6e7Gt8iEPEfThe9dwjkQ9vg+yHt9r-Dtw71XECB9P3Twei5-oG0QvRt3Bx-J6XzAbnK+R+r8ca3LG4-h+RE7+gyJg8V+OK3mv3AYMSDp-3ljUh8OOHBKx9DxGPSt8H8ZyfLBkT9-byZuw8+wgr5RJewjWnaeIkryOqdY6R06+vRrqd+Gj+H6Dykbv66d+hFyDUAoPh7dH7EBuh-nRr9iGP4aP328P+1DX7n6Iit7H5VB5CAHDrf6H7f5L5QE9Zd5v4rrzpjplhAjHBoFDD0Z7674YGn7S5kKyZybcZYwryaQqZqDnqaYvrKiB4Tok5oFAbgCnA0CBAjo4Fl49CV5oGsEn7nosG9ah60Gh76aCFoHCGYG+buQDaqACB0jMBw6ha7b7aHbHZs4kj5bpatapb5YHZHYnbEgAAUAAQroQANIACUF212t292j2z2b2tmsiQIyoLmKG2gOe4AgQmWRWmWWI92V2W2WIAAwmDoSMDt5gAALGBTgkiGGPZWHA7eheaREYCxFGGZbXbpYWG+a2Rfp+DoCKhLr2Z1bua3TejJbebhF2iJAAD2JIXg0Q-w8QAAlnaMMHUXaLkRWECGZOIIoKZgNqFkltUXUTKAVsVqVrZlwD1saKICIExJ4TNmDtEAALarG1F2heDVHuTEA4jei+YyJeGubxabqDYgA7YtHDB2jRDxDVE+HehgDLbsAlBQh274aO6N6Ai8E8GCH75uFDBAA).
Falstad doesn't have 7812/7912 regulators so I just labelled the place where they belong; follow your full schematic. Notice the GND symbol on the transformer CT, between bulk caps, 7812/7912 middle pins, anode of lower TL431, and center output connection.
The +5VREF is derived from the +12 as you've done with resistor+2*TL431 to GND (not the -12V post).
This is good to know because I used -12v for it. I am still not sure how they work to create 5v. But they sure do.
TL431 work like zeners; they shunt/clamp the voltage to their Vz voltage (or programmed via divider resistors on the adjust pin). The 1K resistor is important otherwise you'll kill the zener/TL431. However, shunt regulators are only good for low current loads or for reference use (your case). See here (https://www.electronics-tutorials.ws/diode/diode_7.html) and here (https://en.wikipedia.org/wiki/TL431#Fixed_Zener_Mode).
The "bulk" supply can be just +12 (to +20V) between 2 output posts (not bipolar).
One of the supplies must be fully isolated from PE; have NO continuity from any output post to PE or the (wide) neutral prong (on a polarized wall plug). The latter shouldn't really exist but check anyway.
I have the Transformer a 266L24 2x12 and it can be a 2a or 4a depending on using one or two windings selected by the range switch. I understand I can wire it and use it like a center tap. GND the chassis with the PE not the center winding like the REf. Is that correct?
I think I am just going to wire the Transformers and the bridges and at least know my power is correct.
See attached (second "bulk" power supply).
You still want to keep both ref and bulk supplies isolated from PE; leave that option for the user on the front panel.
Fortunately, the 266L24 (https://www.hammfg.com/files/parts/pdf/266L24.pdf?v=1697661948) secondaries can be wired in series or parallel (https://www.hammfg.com/files/products/266/266-insert.pdf?v=1697662070). See attached for how to wire a DPDT switch for series/parallel duty (from this "Series/Parallel Switching" diagram (https://guitarnuts2.proboards.com/thread/10028/series-single-parallel-using-switches?page=1&scrollTo=105239)). The 470R resistor (R1) is to discharge the cap when changing the switch position to the lower voltage. However, you'll likely need another pole (3PDT) for the switch to short R32+R33 in the CREF generation part of the complete schematic (not shown here).
Wire the primaries for the DP241-5-28 transformer (https://www.belfuse.com/resources/datasheets/signaltransformer/ds-st-241-series.pdf) the same way as shown in the Hammond connection diagram (https://www.hammfg.com/files/products/266/266-insert.pdf?v=1697662070) (notice the dots on the windings). In the DP251-5-28 case, F2 connected to F1 is one mains phase and S2 connected to S1 is the other mains phase. Don't make a mistake or you'll kill the transformer; wire up the mains fuse.
Before proceeding with the regulator parts, wire-up the ref and bulk supplies and confirm that they are producing:
ref: +12V, +5V, -12V relative to 0V/GND (black multimeter lead).
bulk: +12 or +24V (depending on switch position) relative to 0V (black multimeter lead).
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@pqass there is a lot of good info there I will need to digest. I am going to need to study and think about it for a while before I reply. I thought had a better understanding of T1 from a few previous posts with Kleinstein. But I went back and re-read them I realized I had mis-understood what he said. I only absorbed 1/2 of the reply.
I do have few unrelated questions though.
Fuses F-1 and F-2 call for 1 amp 125v solder in fuses, which I found some Littlefuse for. But it list's F-3 as a fusible resistor 1 ohm 5% .5 watt. Is there a different name for this? Because I can not find fusible resistors anywhere?
And it lists the main T-1 fuse F-4 as a 1 amp or 2 amp in a fuse holder. Size depending on if its OE9 or OE3 and I don't understand what that means. The Transformer is 48 VA which I calculate as .4 amps at 120v so I assume the 1 amp is the correct fuse. Am I correct?
Thanks
Therm
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Fusible resistors may be a replacement for low current fuses. For a new build it should be OK to use a suitable low current slow fuse (what ever the transformer can support). The values will depend on the display part.
Fusible resistors are still available, though not longer that common. PTC type fuses can be an alternative in some cases, though the characteristinc and use is different.
For F1 and F2 it is OK to used exchangible fuses with holder instead of a direct solderable. For DIY this may be easier to get.
The input side fuse depends on the line voltage setting: with 230 V main a smaller fuse is sufficient and should be used. 1 A sounds OK, as the transformer can have some turn on spike in the current, both from the transformer and charging the filter capacitors.
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See attached (second "bulk" power supply).
You still want to keep both ref and bulk supplies isolated from PE; leave that option for the user on the front panel.
Fortunately, the 266L24 (https://www.hammfg.com/files/parts/pdf/266L24.pdf?v=1697661948) secondaries can be wired in series or parallel (https://www.hammfg.com/files/products/266/266-insert.pdf?v=1697662070). See attached for how to wire a DPDT switch for series/parallel duty (from this "Series/Parallel Switching" diagram (https://guitarnuts2.proboards.com/thread/10028/series-single-parallel-using-switches?page=1&scrollTo=105239)). The 470R resistor (R1) is to discharge the cap when changing the switch position to the lower voltage. However, you'll likely need another pole (3PDT) for the switch to short R32+R33 in the CREF generation part of the complete schematic (not shown here).
Wire the primaries for the DP241-5-28 transformer (https://www.belfuse.com/resources/datasheets/signaltransformer/ds-st-241-series.pdf) the same way as shown in the Hammond connection diagram (https://www.hammfg.com/files/products/266/266-insert.pdf?v=1697662070) (notice the dots on the windings). In the DP251-5-28 case, F2 connected to F1 is one mains phase and S2 connected to S1 is the other mains phase. Don't make a mistake or you'll kill the transformer; wire up the mains fuse.
Before proceeding with the regulator parts, wire-up the ref and bulk supplies and confirm that they are producing:
ref: +12V, +5V, -12V relative to 0V/GND (black multimeter lead).
bulk: +12 or +24V (depending on switch position) relative to 0V (black multimeter lead).
I think I had an epiphany moment after reading this. It took some study and thought and a bunch of re-reading of previous posts of @Kleinstein, @andrewtaylor and the post quoted. But I think I am understanding much better now. Please correct me if I am wrong.
My first realization was the switch that shorts R32 and R33 is part of the high low range switch not the CC/CV switch. I have corrected that on my drawing. I have now used a split A/B DPDT switch in those locations.
Second As an AC contractor I have worked with transformers for many years. Low voltage, high voltage with parallel and series primary and secondary windings. Now the parallel series switching you simulated is very complex and difficult to understand. I but I do understand what is going on. It will take some serious though to wire it but I will be able to accomplish that. The parallel low volt high amp and series high volt low amp I get that part.
What was and is still confusing to me, is how HP accomplished the high and low range with the transformer configuration shown? It is completely counterintuitive to me. I understand they had a custom wound transformer made. Is that transformers winding not balanced and one half is higher amp than the other half?
Is it possible to lower the amperage when switching to low range and using the whole winding rather than just one or half a winding? Is the upper winding so much lower in amperage that it lowers the overall when both are in the circuit?
Sorry if this is a dumb question but it is what is confusing me.
Also I found a triple pole double throw 125v 15a switch at DigiKey. I think that should be able to accomplish what I need to do. Is that correct or is my epiphany just indigestion:)?
Also thanks for that TL431 info it can be wired in so many ways pretty versatile little component. And for taking the time to create those simulations.
Thanks
Therm
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I don't know the details of the HP transformer switching. It is common to have transformer tap switching with just using more or less windings in series, not no extra parallel connection. This does help with reducing the power loss, but does not allow for a higher current at low voltags (at least not much and not higher current limit used). The standard way (e.g. used in many supplies, even the cheap ones) for tap switching is automatic with a relay, based on the actual output voltage. The question is a bit if 2 , 3 or 4 settings are used.
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I realize that I am repeating Kleinstein but..... My understanding in the dual winding transformer is that the reason for this is to have less voltage lost in the final pass transistors. The pass transistors do not have to bring down the incoming voltage as much and hence there is less heat generated. I have a PS that does this. They use a relay that switches the transformer secondaries. This is automatic in that when you increase the voltage to a certain point there is a sensing circuit that switches the secondaries "automatically". You could use a switch but if you left in in High position and dialed down the volts, the final transistors could get hot.
There is a bit of a jump in the voltage when the relay switches, this is not entirely a smooth transition.
The PS I have seen only use one of the secondaries for low volts and then both in series for higher volts. Have not seen one that uses secondaries in parallel.
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What was and is still confusing to me, is how HP accomplished the high and low range with the transformer configuration shown? It is completely counterintuitive to me. I understand they had a custom wound transformer made. Is that transformers winding not balanced and one half is higher amp than the other half?
Is it possible to lower the amperage when switching to low range and using the whole winding rather than just one or half a winding? Is the upper winding so much lower in amperage that it lowers the overall when both are in the circuit?
The load decides how much current to draw from the secondary (even beyond the amperage spec). At least until the wire decides to act like a fuse.
HP protects the transformer by limiting what the maximum CREF voltage will be. See attached and simulation here (http://www.falstad.com/circuit/circuitjs.html?ctz=CQAgjCAMB0l3BWcMBMcUHYMGZIA4UA2ATmIxAUgoqoQFMBaMMAKACcRcAWETFELtn58oIDMTjsBQ3hn4JCVEVTDxIU7rP5hiwuaOwT1AJXC6t4Lj2WiutUVRgIWAQ2n9s2QhUWcvIPHAkJiRVNUdYeEIhPDJIBDRxLgTiUTD4FgB3d040HOUsnypPbwUlfXUAcxzsBJrCQMdCsotCFGsKlgAHEDaO-j7OOuwHFmrB2oH2zgbR7MGRHG8CjiWLNew8Hlo1KQ2tsX8uPEdeSirD72OqNa5ibyaek+KD54ETzjmAuE4D-e2xt8qNcgQJ7l8dMJppCLOpspoUNMEZ0AB69LC8Qg8HDWQjkaw8ADCxgAogAxFhohqpbCCMR5WlXcCBYztSm9PCBKw3HQCOk8MAslDYdlWQKI2gYAk8AWBQkAVzYbDoADsAC4AHQAzoSAPbqti6gA2Go1KuMOm1Lk1WoAZvKjSadQB1dk6Yr4TFIbDMATMkDGIQarqBkVon2BXA04gjH38WUBn3B1l4N0ESzebAYFTECAJgDKzpQppVAAsAJaVUvagDGiuV6u15a12sJABkAPL5kkAERLRt1mVr9dVNub2o7AAUSQA5FhasxQngI6anW0uI1augsIA).
With SW2 shorting R32+R33 (the high current, low voltage position), CREF is high enough to produce 300mV across R23.
With SW2 open (low current, high voltage position), CREF is only high enough to produce 200mV across R23.
300mV is the voltage drop on shunt R2 if 3A flows through it.
200mV is the voltage drop on shunt R2 if only 2A flows through it.
The CREF voltage is the ceiling that kicks-in constant current mode.
We don't know what the wire gauge of the lower (than the tap) secondary winding vs. upper secondary winding. For all we know, HPs custom transformer has a thicker gauge lower winding allowing one to draw more current while keeping under the max. VA. I do know from another post, the upper and lower windings aren't equal. They measure different ohms.
In my last simulation, I used a DPDT to double the current/half the voltage via parallel/series connections because that is the manufacturers recommend approach. Their windings are what you'd expect; same length and gauge.
Also I found a triple pole double throw 125v 15a switch at DigiKey. I think that should be able to accomplish what I need to do. Is that correct or is my epiphany just indigestion:)?
It's more than enough.
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The load decides how much current to draw from the secondary (even beyond the amperage spec). At least until the wire decides to act like a fuse.
Occam's razor :)
HP protects the transformer by limiting what the maximum CREF voltage will be. See attached and simulation here (http://www.falstad.com/circuit/circuitjs.html?ctz=CQAgjCAMB0l3BWcMBMcUHYMGZIA4UA2ATmIxAUgoqoQFMBaMMAKACcRcAWETFELtn58oIDMTjsBQ3hn4JCVEVTDxIU7rP5hiwuaOwT1AJXC6t4Lj2WiutUVRgIWAQ2n9s2QhUWcvIPHAkJiRVNUdYeEIhPDJIBDRxLgTiUTD4FgB3d040HOUsnypPbwUlfXUAcxzsBJrCQMdCsotCFGsKlgAHEDaO-j7OOuwHFmrB2oH2zgbR7MGRHG8CjiWLNew8Hlo1KQ2tsX8uPEdeSirD72OqNa5ibyaek+KD54ETzjmAuE4D-e2xt8qNcgQJ7l8dMJppCLOpspoUNMEZ0AB69LC8Qg8HDWQjkaw8ADCxgAogAxFhohqpbCCMR5WlXcCBYztSm9PCBKw3HQCOk8MAslDYdlWQKI2gYAk8AWBQkAVzYbDoADsAC4AHQAzoSAPbqti6gA2Go1KuMOm1Lk1WoAZvKjSadQB1dk6Yr4TFIbDMATMkDGIQarqBkVon2BXA04gjH38WUBn3B1l4N0ESzebAYFTECAJgDKzpQppVAAsAJaVUvagDGiuV6u15a12sJABkAPL5kkAERLRt1mVr9dVNub2o7AAUSQA5FhasxQngI6anW0uI1augsIA).
With SW2 shorting R32+R33 (the high current, low voltage position), CREF is high enough to produce 300mV across R23.
With SW2 open (low current, high voltage position), CREF is only high enough to produce 200mV across R23.
300mV is the voltage drop on shunt R2 if 3A flows through it.
200mV is the voltage drop on shunt R2 if only 2A flows through it.
The CREF voltage is the ceiling that kicks-in constant current mode.
Great explanation and simulation.
We don't know what the wire gauge of the lower (than the tap) secondary winding vs. upper secondary winding. For all we know, HPs custom transformer has a thicker gauge lower winding allowing one to draw more current while keeping under the max. VA. I do know from another post, the upper and lower windings aren't equal. They measure different ohms.
This would explain a lot and make a lot of sense.
In my last simulation, I used a DPDT to double the current/half the voltage via parallel/series connections because that is the manufacturers recommend approach. Their windings are what you'd expect; same length and gauge.
Understood
It's more than enough.
Thank you. I was hoping to use three of the same style rocker switches (though different in function) for three main switches. I not only want a professional quality functioning device, I would also like it to be professional looking. You know both form and function, built with craftsmanship. Function is the obvious priority, so if I need to use a toggle style for the range switch, I will.
My goal has been for this project to replicate the HP 3610 as closely as possible and for it to be an educational and enjoyable experience. Thanks to the folks here on this site, it has been both so far, no doubt. If I need to make the previously discussed adjustments I will. But before I do I am going to do a few things.
I will look into seeing if I can have the HP transformer replicated relatively inexpensively. Not a solder in but a wire in type configuration. This will simplify the design and build. I have done some research and have become aware of a company, Heyboer Transformer that does small custom work. My understanding is they do this at very reasonable prices. Reasonable being relative I guess. I will see if I can get a quote from them and see if it is reasonable to me.
I will send them the part of the schematic with the transformer. Then what do I ask for the main to be? 2 x 12v hi-range 3 amp, low-range 2 amp. The reference to be 2 x 14/15v 250mA and the display to be either 8/10v 150mA. I don't want to order the wrong thing. :)
If the above does not work out I will try to contact Hammond and ask if the 266l24 can have a single winding pushed to three amps. Likely the answer would be no (if they even responded) but it can't hurt to ask.
Or maybe just buy a Hammond 266M24 or 266N24 with which a higher amp single winding would support the more simple SPDT wiring. Since the CREF is controlling the output it would not seem to matter if the series connection were higher than two amps. Is this correct thinking or am I off in LaLa land somewhere? :)
Thanks
Therm
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I was able to contact the custom transformer manu they are nice people. Their prices seem reasonable and very close to the price of purchasing three separate transformers. So far Just ballpark prices so I could have an idea of price. I did not waste their time if too much $$.
I discussed with him what I am trying to accomplish and what I think? I need. But after re-reading @Kleinstein and @pqass so many times and still not always getting it right. I just want be sure I am giving the manu the correct info. I sent the original and my re-draw schematic for his review. Plus I gave him the the info on volts and amps I desired. Below is the discussion starting with his reply after our intial conversation.
Manu Rep, I now come up with 24VAC CT @ 3A winding =72 VA , 28 VAC CT @ 300mA =8.4 VA , and 5 VAC @ 100mA =5VA . Total 85 VA transformer. This look correct ? I know you draw the higher current at half the winding( at center tap ground ) so am winding the whole thing for higher current . I can go a bit more for a buffer , never hurts to over build a bit and also use grain oriented laminations, keeps it cooler running.
My reply, was that I think I need more Voltage on the 5v display section for the 7805 regulator to work. Like maybe 7- 8v. And having the extra buffer sounds good.
His reply, Doing it on a 1 ¼ E center leg , footprint will be 2 ½ X 2 7/16 4 screws, vertical end bells. Arlyn does hard quotes, i just guess best i can. Ill get back with price. I can tic up the 5 volt a bit right now its at 5.36 vac with exact 120 in.
PS, each turn on the 5 volt = .33 volt. 16 turns = 5.36 , 17 turns = 5.69 etc..
After re-reading again I am thinking the primary needs to be a bit higher amperage 3.3 or 3.4 amp. I am not confident enough in my knowledge to buy this transformer without some help from the folks here on this site. So @Pqass @Kleinstein any input?
Right now I will use the transformers I have already purchased to continue testing. By manually switching between series and parallel with wire nuts. I am scrounging for a cabinet or enclosure to mount them in. So I can just run only the secondary wires out to the bridges for safety reasons. Then I will use them somewhere down the road in something. If not I will consider it the cost of education.
Thanks in advance
Therm.
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So as a safe side recommendation: a 120VA toroid core as a solid is what I would use.
120VA toroid should be standard value, at least at the manufacturers I buy from it is.
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A LED display may need quite some current from the 5 V rail. AFAIR the ICL7106 has some 7 mA per LED and thus ~ 50 mA per digit and thus some 170 mA worst case. More modern LEDs may get away with less current though.
So I would look more for 300 mA DC (500 mA AC) for the 5 V part.
To get 5 V via a 7805 regulator it need way more than 5 V AC. The old standard was 10.5 V AC to regulation to 5 V. One may get away with 9 V and a little less (e.g. 8 V) when using a low drop out regulator instead of the 7805 and accepting some ripple at low mains voltage.
For the main current it need some 1.6 - 1.7 A AC for 1 A of DC. So the 3.4A would be good for about 2 A DC out.
The regulator part can likely get away with less than +-12 V. The current would be mainly for the fan. The regulator part itself needs little current.
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I am shortly at forum. I have no time to read now 150 posts to know everything what was said.
I will just say something that you probably ignore as possibilities are now much higher then when I was doing my linear supply, but who knows may be you will like the idea.
I have done it (first version) when I was about 15 (later I few times made some improvements). Supply was for me first 'must have'. Then whatever I wanted to do I always found that some measurement equipment would be need to do this so each time decision was: let do it first. This way I made analog C meter and frequency meter. Both together with LC generator I used to measure L. The top 'must have' was for me oscilloscope, but I have made it long time later - finished it when I was 24.
In supply I used 100W trafo from tube radio receiver. I disassembled the entire core and unwrapped the anode winding. I replaced it with my winding in a 6+6+6+6+6+1+1+1+1+1 (Volts) arrangement.
All taps are placed on the front panel (wooden plywood casing) so using two banana plugs I can choose any voltage from 1 to 35V in 1V steps and feed it to the rectifier and then the stabilizer (voltage and current). That way I can avoid dissipating too much power in regulating transistor (2N3035 if remember well - 50 years passed). I am still from time to time using this supply.
I wanted to say only about these 6+6+...+1 solution. May be you will like it.
Having these taps at front allow also to use it as AC supply. If it happens that you will need to get high voltage to test something you can use trafo and power its low voltage coil with any 1V..35V AC to get different voltages at its high voltage coil.
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For a no-effort, off-the-shelf solution, use your existing Hammond 266L24 for the main transformer and add this Signal 14A-30-512 (https://www.belfuse.com/resources/datasheets/signaltransformer/ds-st-14a-triple-series.pdf) 30VA transformer with dual isolated secondaries (±12VDC@250mA + 5VDC@1.25A after regulation) for the op amp and meter+fan supplies. See Digikey here (https://www.digikey.com/en/products/detail/signal-transformer/14A-30-512/1117954).
If you want just one transformer, it wouldn't take much effort to start with a 50VA (open center) toroidal with dual (2x12VAC) secondaries and add your own bifilar 15VAC and 9VAC windings; like the Hammond 182L12 (https://www.hammfg.com/electronics/transformers/power/1182) or the Triad Magnetics VPT24-2080 (https://www.farnell.com/datasheets/2279614.pdf) (only one left at Newark/Farnell). I don't think the additional windings will draw much power away from the existing windings. And take care not to accidentally create a shorted turn with the mounting bolt.
I'd leave the ±12VDC for the op amps and use the 5VDC for the meters and (5V@200mA) fan.
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For the main current it need some 1.6 - 1.7 A AC for 1 A of DC. So the 3.4A would be good for about 2 A DC out.
This is the part that I was misunderstanding. Initially I thought you meant 1.6 amps AC input to the primary to output 1 amp output to the secondary.
So if am understanding correctly now? For every 1.6 or 1.7 amp AC out of the secondary I will be able to produce 1 amp DC out of the bridge?
This would mean I need an additional 1.6 or 1.7 amps added to the 3.4 amps for a total of 5.1 amps to output 3amps DC after the bridge?
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To get
5 3 A DC out after the filter capacitor one would get an AC current of some 5 A and thus need a corresponding winding. A 3.4 A rated winding would be OK for a 2 A supply.
The extra factor comes from the pulsed current and thus an RMS current higher than the averaged current that contributes to the DC current.
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For a no-effort, off-the-shelf solution, use your existing Hammond 266L24 for the main transformer and add this Signal 14A-30-512 (https://www.belfuse.com/resources/datasheets/signaltransformer/ds-st-14a-triple-series.pdf) 30VA transformer with dual isolated secondaries (±12VDC@250mA + 5VDC@1.25A after regulation) for the op amp and meter+fan supplies. See Digikey here (https://www.digikey.com/en/products/detail/signal-transformer/14A-30-512/1117954).
If you want just one transformer, it wouldn't take much effort to start with a 50VA (open center) toroidal with dual (2x12VAC) secondaries and add your own bifilar 15VAC and 9VAC windings; like the Hammond 182L12 (https://www.hammfg.com/electronics/transformers/power/1182) or the Triad Magnetics VPT24-2080 (https://www.farnell.com/datasheets/2279614.pdf) (only one left at Newark/Farnell). I don't think the additional windings will draw much power away from the existing windings. And take care not to accidentally create a shorted turn with the mounting bolt.
I'd leave the ±12VDC for the op amps and use the 5VDC for the meters and (5V@200mA) fan.
Yes I would like to simplify down to a single transformer if possible . But I am not sure I am ready to build a transformer yet. Something that is confusing me is if there is a 1.7 to 1 ratio like noted by Kleinstein, how can the 266L24 in parallel @4 amps produce 3 amps after the bridge. There must be something I am not understanding.
I have rounded up an enclosure for my transformers and hope to resume testing with the correct isolated power supplies. Per your suggestions. Regarding the protective earth ground should it land on the transformers metal case? If not where should I land it?
Thanks
Therm
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To get 5 A DC out after the filter capacitor one would get an AC current of some 5 A and thus need a corresponding winding. A 3.4 A rated winding would be OK for a 2 A supply.
The extra factor comes from the pulsed current and thus an RMS current higher than the averaged current that contributes to the DC current.
Did you mean the part highlighted in red to be 3 not five?
Thanks
Therm
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Of cause it should be 3 A DC. ( A add a note to the old post).
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I have the tranformers and bridges in the circuit now. I mocked up the reference and bias and series pass and voltage control and could get no output from the Darlington. Pin two had power out of the bridge 16v. So I decided to complete the CC/CV indicator circuit as well. Just to be complete.
When transformers are energized I have CC and CV LED lit constant. According to the manual the CC should only be on only when there is current present and CV always on when unit powered. I have no load on the Darlington output should be no current. This has me confused.
I did find a wiring error. I created a small island for S+ then jumped it to the end of the output rail. My jumper was off by one row in the BB, so S+ was not getting to the output rail. This caused the 7812 to get real hot. I noticed it before I fried the 7812 but not before toasting a TL431.
After correcting S+ my -12 and +12 were working but I lost my 5v ref. Then I noticed the Breadboard holes of the TL431s were in melted a bit. I tested them One was bad so I replaced it and changed the BB location. 5v ref was now restored.
I do have V out of the darlington now but it is only 200mv to 3.1 v. I hit 3.1 v after only a few turns of the V Adjust Pot R-37 then I see no more increase. I should be getting at least 8V.
Measuring v on the Darlington Pin 1 to CT GRD. I get 600mv to 1.1v in the first few turns of the Voltage adjust Pot. Anyone have suggestions for what I should check? Or any idea of what could be wrong?
Thanks
Therm
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So as a safe side recommendation: a 120VA toroid core as a solid is what I would use.
120VA toroid should be standard value, at least at the manufacturers I buy from it is.
I am not sure I understand what you mean here.
Are you saying to ask the manu to use a 120va torrid core rather than a standard iron?
If you want just one transformer, it wouldn't take much effort to start with a 50VA (open center) toroidal with dual (2x12VAC) secondaries and add your own bifilar 15VAC and 9VAC windings; like the Hammond 182L12 (https://www.hammfg.com/electronics/transformers/power/1182) or the Triad Magnetics VPT24-2080 (https://www.farnell.com/datasheets/2279614.pdf) (only one left at Newark/Farnell). I don't think the additional windings will draw much power away from the existing windings. And take care not to accidentally create a shorted turn with the mounting bolt.
After thinking about this I may just buy that toroid today. If only for experimentation with winding my own additional secondaries. It sounds very interesting. After thinking about it I realized I have wound toroid transformers before. Just not power transformers. In making Ham radio antennas I have made BalUn and UnUn toroidal transformers.
Also I bought a 5135 display. I thought I ordered a 5/10/20 volt range but by mistake I ordered a 50/100/200 mv range. It was only $4 and change not worth returning. I will keep it and order another. The chip on it was not a dip it is a tiny square MQFP package I think its called.
Thanks
Therm
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The control part can get way with less than +-12 V with no problem. Except for maybe the 5 V ref. part it should also would with some +-5 V supply. This means less added windings for the toroid. Depending on the display unit it may even use the same supply too.
Finding errors in the breadboard circuit is tricky from remote. For the start one could skip on the transformer tap switching.
A point to look at are the 2 regulator OP-amp outputs: one (usually the CC part) should be all the way to the positive side and the other adjusting somewhere in the middle (e.g. 0.5 V) adjusting the output current.
Toasting the TL431 is odd, as this part should have a current limiting resistor in sereies and see a limited power.
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These are my readings
LM358 Pin 1, 3.98v Pin 7, 1.2V
LM393 Pin 1, -4.5v Pin 2, -4.7v
LF411 Pin 6, -.3v Pin 2, 0v Pin3, 0v
Regarding the TL431. After your post I put it back in the circuit to see if maybe I was wrong and my 5v ref output went up to 8v. Also the one that toasted was the second one after the resistor.
I for some reason bought a TL071 is that similar to a LF411?
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The TL071 is very similar to the LF411, so no problem there. -0.3 V at the output would suggest calling for a just off the output stage. So the voltage regulation seems to be active. Pin 7 of the LM358 should be the current regulator part. Here the 1.2 V are odd - this should be more like 9 V or so. 1.2 V DC would still allow the output to be on, but chances are this part is oscillating and the 1.2 V are only an average. This could also explain the -4.5 V for the CC indication. For a test one could use a much larger capacitor for C12 to slow down the current regulation to make it stable for the start. The LM358 is not a good choice and could be prone to oscillation from it's rather large dead zone.
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The TL071 is very similar to the LF411, so no problem there. -0.3 V at the output would suggest calling for a just off the output stage. So the voltage regulation seems to be active. Pin 7 of the LM358 should be the current regulator part. Here the 1.2 V are odd - this should be more like 9 V or so. 1.2 V DC would still allow the output to be on, but chances are this part is oscillating and the 1.2 V are only an average. This could also explain the -4.5 V for the CC indication. For a test one could use a much larger capacitor for C12 to slow down the current regulation to make it stable for the start. The LM358 is not a good choice and could be prone to oscillation from it's rather large dead zone.
I was probing looking at all pins on all amps and I found that I had no -12 on the lm358. I found a loose connection and fixed it and the cv light went out. I continued probing and when probing the lm358 pin 1 the CC light went out and CV came back on. Now CV stays on and CC comes on only when I probe pin 7 and it goes out when I remove the probe.
358 Pin 1, 3.5v Pin 7, .6v when probing.
LM393 Pin 1, 9-10v Pin 7, -4.7v.
LF411 Pin 2 and 3, 0v Pin 4 -12v Pin 6, -.3v Pin 7,+12
Darlington Output tops out at 2.5v between neg out and pos out rails.
I have the TL071 as a spare but I am using the LF411. Not sure if I was clear on that.
Also what is a better choice for the 358 in a dip package?
I am going to re-check all wiring and connections again.
Thanks
Therm
PS Pin 1, on the Darlington adjusts between .5 and 1.2v with the v adjust Pot.
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A slight upgrade from the LM358 would be a RC4558 (or similar from other manufacturer). Still not great, but less cross over distortion and related delay, less noise and a bit more speed and still not too fast for the bread board. For a final version I would use 2 single OP-amps and possibly an OP27 or OPA207 or maybe OPA202 for the current regulator, as here low drift and noise could really matter and allow for a smaller shunt. Not sure if the speed matters - it could as the shunt votlage is small to start with. The 2nd OP-amp for the ref. voltage is less critical and could be 741 or LM358.
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I re-made some of the readings in my last post the changes are in red. I am not sure how I got them wrong the first time.
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I have re-double checked everything on my circuit. If there is a wiring flaw I don't recognize it as such.
I did try a larger cap at c12 even though the light is out now. It did make the light not go out as quickly when I remove the test probe from pin 7. Just a bit more delay. I'm glad I did, it helps me to understand what that cap is doing.
https://tinyurl.com/23j2679m
The above link is the simulation @pqass made. If I am understanding it correctly Pin 3 of the LF411 should move between 2.25mv and 1.25v when the adjust pot moves from stop to stop? I Is this correct? Because I have 0 v at that pin. My five volt reference stops after the 14.3k (15K in the Sim) resistor between the 5V Ref and Pin 3. Am I understanding this correctly?
Thanks
Therm
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I'm glad you're focusing on the core part of the circuit. There's no point in adding more (current limiting, CC/CV indicators) until you build a working foundation.
Review the golden rules of op amps (https://www.circuitbread.com/ee-faq/what-are-the-golden-rules-of-op-amps); especially the 3rd where the difference between +/- inputs should be zero in a steady-state negative feedback arrangement.
Below, I walk-through how the voltage regulation works via negative feedback (refer to the simulation in your last message and your latest schematic). Lets start...
a. The default position of the darlington Q1 is fully on via R3 (1.2K) to +12V (ref+bias supply).
b. If the darlington is fully on then the unregulated source voltage (to its left) is let through to the output (right side) with minimal voltage drop.
c. Notice the GND symbol on the +OUTPUT that ties the GND of the ref+bias supplies (+12V, -12V, +5VREF) to this point.
d. If the full unregulated source voltage is let through, then the -OUTPUT is the negative of the unregulated source voltage (in our case the battery symbol) relative to the same GND.
e. We have a resistor divider between the lower -12V (fully unreg. source voltage), the voltage adj. pot R37, R15 (15K), and +5VREF.
f. Given that +5VREF being relative to the same GND point on +OUTPUT,
if the fully unregulated source is let through, that makes it 12V (full unreg. source voltage) + 5VREF = 17V across the pot R37 and R15.
g. Lets say the pot is half-way (25K), then we have 17V across 25K+15K=40K.
Q: What's the voltage at the mid-point between them?
A: 25K/40K=0.625*17V=10.6V (lower) and 17V-10.6V=6.4V (upper)
h. The +5VREF is like an anchor; it's always +5V from GND (via TL431 regulator action).
Given the upper part of the divider being 6.4V to the mid-point, that places the mid-point below GND (+5VREF-6.4V=-1.4V).
i. The mid-point is connected to +Vin of the op amp, the -Vin is tied to GND.
So now +Vin is lower than -Vin! This causes the output of the op amp to swing negative.
j. The negative-going op amp output flows through the diode to turn-on Q2 (PNP),
which lowers the current to the darlington (via Q2 winning against R3),
which (Q1) is no longer fully-on (acts like a growing resistor with a growing voltage drop lowering the voltage going from left to right side),
which lowers the voltage between R15+pot divider,
which lowers the voltage on the upper and lower legs of the divider to the point where the mid-point is no longer negative WRT -Vin of the op amp.
k. The op amp will closely watch any difference between +Vin and -Vin and give a negative kick or back-off (output a positive voltage) to let R5 turn-off Q2, letting R3 turn-on the darlington a bit more.
l. Until you change the the adj. pot and the op amp needs to seek a new equilibrium.
m. Nothing is instantaneous. The unregulated source voltage takes time to ramp up, the op amp also takes time to swing positive or negative, etc.
The actions above will kick into regulation as soon as +Vin is lower than -Vin and won't let a -1.4V difference happen.
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@pqass.
That explanation will take some time for me to fully digest. I was totally misunderstanding the function of the op amp. You have provided me with a good sequence of operation to logically follow to try and trouble shoot my issues. Knowing what is supposed to happen, will help me try and find out what is not happening.
Thanks
Therm
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I have tested and checked and re-checked. I am only getting adjustment on my output from 0-2.7 V. This is low range and I should be getting 0-8 V. It hits 2.7 at about 3-4 turns and goes no higher. I did all the math and tried to match the sample @pqass provided and Vin - And Vin + do remain at 0. Pin 6 will vary from -.81 to -.24 from stop to stop on the main Pot. Using a TL071 had no effect readings were pretty much the same. So I am back with the LF411.
I even walked away from it for two days just to clear my mind in case I was too focused and could not see the obvious. On the positive side I did already receive my custom transformer. It came much faster than I thought it would. I have yet wire it in to my circuit yet but it looks like a very good quality build.
I am posting a table of my readings comparing it to pqass's simulation. I am thinking about trying a spare TIP 142 thinking maybe I damaged the one in use. I would have done that already but it requires me soldering jumper wires onto it so it will plug into the Bread board. I am not really that hopeful replacing it will make a difference because I am getting 2.7 V of adjustment. I figure if it were bad it would not do that. But who knows.
Any suggestions for trouble shooting would be appreciated. I may just have to pull everything off the board and try again.
Thanks
Therm
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The zero volts between the opamp inputs indicates that it has control of the loop. Does it stay at zero when the pot is turned passed to point where the output stops increasing passed 2.7V?
Although I dont think it is the cause, check for oscillation at the opamp's output.
The output should go to full voltage when the loop is broken by removing the diode or disconnecting the pot.
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Just to confirm,
the op amp power supply MUST be +12V (pin 7) and -12V (pin 4, not GND/+OUTPUT).
And a multimeter (set to DCV) between pin 7 (red lead) and pin 4 (black lead) should be 24V.
The TL071 is not a rail-to-rail op amp and the 0.299V output (pin 6) smells like it's the max. lower excursion.
The output (according to the simulation) should be -158mV (below GND/+OUTPUT).
Also, verify
that if you were to disconnect the emitter of Q2 (2N4036) from the base of Q1 (darlington), leaving the 1.2K pull-up between darlington base and +12V, that the output (DCV between +OUTPUT and -OUTPUT) should be just a bit below the +17V (unreg.) source voltage.
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I mocked up the circuit in the simulation, minus the diodes. Works fine, just some ringing on load transients due to having no frequency compensation.
This is of little direct help except to prove that the design is ok.
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I mocked up the circuit in the simulation, minus the diodes. Works fine, just some ringing on load transients due to having no frequency compensation.
This is of little direct help except to prove that the design is ok.
Loop always stays at 0. If I remove the diode Reading is 10.6 V. Removing the Pot has no effect.
I am not mocking up the sim exactly. I am mocking up my circuit which is very similar to it. (see pic)
Thanks
Therm
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With the pot removed, the opamp's + input must pull to REF, causing the opamp's output to swing hard positive, assuming the - input is tied to S+.
Edit: remove CR7.
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Just to confirm,
the op amp power supply MUST be +12V (pin 7) and -12V (pin 4, not GND/+OUTPUT).
Yes Pin 4 and 7 are regulated power. 7) +12.04 and 4) -11.96
And a multimeter (set to DCV) between pin 7 (red lead) and pin 4 (black lead) should be 24V.
Yes it is 24.05 V
The TL071 is not a rail-to-rail op amp and the 0.299V output (pin 6) smells like it's the max. lower excursion.
The output (according to the simulation) should be -158mV (below GND/+OUTPUT).
I am using the LF411 I only tried the TL071 briefly. Pin 6 is -.318 v
Also, verify
that if you were to disconnect the emitter of Q2 (2N4036) from the base of Q1 (darlington), leaving the 1.2K pull-up between darlington base and +12V, that the output (DCV between +OUTPUT and -OUTPUT) should be just a bit below the +17V (unreg.) source voltage.
If I pull the emitter of Q2 I get 15.52 V at the output between +/-.
Thanks
Therm
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I don't know the details of the HP transformer switching. It is common to have transformer tap switching with just using more or less windings in series, not no extra parallel connection. This does help with reducing the power loss, but does not allow for a higher current at low voltags (at least not much and not higher current limit used). T
In the original HP supply,
the wire for the lower voltage range has higher diameter.
That's why with simple tap switching (not the more complicated series-paralle scheme I usually use) HP has higher current at he lower voltage range.
Or to keep a long story short:
it's a specialls manufactured/wound transformer .-)
Knowing this, the trick is easily done :-DD
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I have tested and checked and re-checked. I am only getting adjustment on my output from 0-2.7 V. This is low range and I should be getting 0-8 V. It hits 2.7 at about 3-4 turns and goes no higher.
Ttry to remove the LM358 that you planned for curent control.When the voltage control then works as planned, remember the old trick for HW debugging:
If control loops interact, try to seprate them.
Of course, be careful NOT to short the output when there is no CC loop due to removed LM358 :o
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CR6, if damaged, is also capable of causing the present fault state.
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I have tested and checked and re-checked. I am only getting adjustment on my output from 0-2.7 V. This is low range and I should be getting 0-8 V. It hits 2.7 at about 3-4 turns and goes no higher.
Ttry to remove the LM358 that you planned for curent control.When the voltage control then works as planned, remember the old trick for HW debugging:
If control loops interact, try to seprate them.
Of course, be careful NOT to short the output when there is no CC loop due to removed LM358 :o
I did this at your suggestion and it had and it no effect.
Thanks
Therm
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CR6, if damaged, is also capable of causing the present fault state.
I removed CR6 and CR7 one at a time with no change to pin 3. It stayed at 0.
Thanks
Therm
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Either the current path from REF to pin 3 is open circuited or some low resistance path from pin 3 to S+
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Either the current path from REF to pin 3 is open circuited or some low resistance path from pin 3 to S+
I have 12k Ohms resistance between Pin 3 and 5v ref.
Pin 3 to S+ Junction 13.8k Ohms.
Thanks
Therm
Edit: I did discover an intermittent connection on the anode side of CR7 and I corrected the fault. Now my output only adjusts to 1.6V. Pin 2 and 3 are still zero, Pin 6 is .98V when Pot is 0 ohms and .54v at 50k ohms.
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Although my mock-up uses an LM358, I will state the pins for a single opamp.
With nothing else but a 10K resistor connecting my 5V REF to pin 3, I measure 5V on pin 3. Pin 6 measures 10.7V.
The main output measures 14.7V with a 1K load with 15V unregulated input.
This condition must be able to be replicated.
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See attached for a minimal breadboard version of the voltage regulator only schematic from reply#176.
I left out the Q2 (PNP) base protection diode and made the following substitutions (what I had on-hand):
- TL081 op amp,
- Q1=2SC1983 darlington,
- Q2=2N3906,
- op amp output diode is some random signal diode,
- 12K vs 10K load resistor, and
- 68K trimmer pot vs. 50K for voltage adjustment.
A isolated 3-output power supply provided +12, -12, +5; all tied to the same GND. I didn't have a TL431 to generate +5VREF from the +12V. The "unregulated" source supply was provided by another entirely separate isolated +20V supply.
I was able to vary the output voltage from below 1V to 19V, although, I only had a voltmeter attached with no significant load.
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@Therm Mr.
Have a look at Elliot Sound Products website sometime - under Power Supply Design
It helped me understand transformer specification and loading for DIY power supplies.
enut11
https://sound-au.com/articles/index.htm#psud
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@Therm Mr.
Have a look at Elliot Sound Products website sometime - under Power Supply Design
It helped me understand transformer specification and loading for DIY power supplies.
enut11
https://sound-au.com/articles/index.htm#psud
Thanks that is a nice reference.
Thanks
Therm
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See attached for a minimal breadboard version of the voltage regulator only schematic from reply#176.
I left out the Q2 (PNP) base protection diode and made the following substitutions (what I had on-hand):
- TL081 op amp,
- Q1=2SC1983 darlington,
- Q2=2N3906,
- op amp output diode is some random signal diode,
- 12K vs 10K load resistor, and
- 68K trimmer pot vs. 50K for voltage adjustment.
A isolated 3-output power supply provided +12, -12, +5; all tied to the same GND. I didn't have a TL431 to generate +5VREF from the +12V. The "unregulated" source supply was provided by another entirely separate isolated +20V supply.
I was able to vary the output voltage from below 1V to 19V, although, I only had a voltmeter attached with no significant load.
I am going to mock this simple circuit up on a separate board before I un-plug everything and start over. When I pull Q2 I get 15+V on my output. So I am thinking something controlling Q2 is awry.
Thanks
Therm
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With the pot removed, the opamp's + input must pull to REF, causing the opamp's output to swing hard positive, assuming the - input is tied to S+.
Edit: remove CR7.
I did remove CR7 again and my output returned to 2.5v from 1.6 v. and stayed there even after I replaced it. ???
CR6, if damaged, is also capable of causing the present fault state.
I checked it and will check it again.
Thanks
Therm
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Keep in mind that one or more of the opamps might be damaged by previous wiring mistakes.
Be certain that the simple test in Reply #193 can be replicated.