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Linear power supply project

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Therm Mr.:
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. :)


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.

1) TIP36CTIP147 (PNP darlington) is a readily available substitute in a TO-247 package instead of the original 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 page A-6 to A9.

EDIT: according to the service manual the series pass transistors should be 2N6056 not "36"; typo?  This is an NPN darlington part. As such use the TIP35CTIP142 instead.

2) Instead of the LM336BZ5.0 you can use a common TL431 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 (and this one too).  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.

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.


--- Quote from: Kleinstein on June 12, 2024, 06:35:57 am ---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.

--- End quote ---

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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