Author Topic: Linear lab power supply  (Read 85410 times)

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Offline JuanGgTopic starter

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Re: Linear lab power supply
« Reply #325 on: January 20, 2019, 05:30:16 pm »
Just thought of a neat idea for my project.
A diode in series with a piezo buzzer across the output terminals will give immediate indication that reverse polarity has been applied.
I like that idea. I had thought of a led indicator or something, but a buzzer will definitely warn you before something blows up.

Offline JuanGgTopic starter

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Re: Linear lab power supply
« Reply #326 on: January 20, 2019, 05:48:36 pm »
Here is what I have on the PCB. I still have to make some final touches, but I think this is what I'm going for. I'll wait a couple days before ordering should anyone want to take a look and suggest any changes.
xavier60, I hope you don't mind to be included on the silkscreen, that is the least I can do.
    Juan
« Last Edit: January 20, 2019, 10:25:42 pm by JuanGg »
 

Offline xavier60

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Re: Linear lab power supply
« Reply #327 on: January 20, 2019, 10:26:29 pm »
xavier60, I hope you don't mind to be included on the silkscreen, that is the least I can do.
    Juan
I don't mind.  :)
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Offline xavier60

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Re: Linear lab power supply
« Reply #328 on: January 20, 2019, 10:32:33 pm »
Here is what I have on the PCB. I still have to make some final touches, but I think this is what I'm going for. I'll wait a couple days before ordering should anyone want to take a look and suggest any changes.
xavier60, I hope you don't mind to be included on the silkscreen, that is the least I can do.
    Juan
Can you post a schematic mainly of the PWM filters and measurement op-amps areas?
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Offline JuanGgTopic starter

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Re: Linear lab power supply
« Reply #329 on: January 20, 2019, 10:55:00 pm »
Quote
Can you post a schematic mainly of the PWM filters and measurement op-amps areas?

Attached are the full schematics. I don't know if I should stick with the RC filters or not.They seemed to do just fine. The spare op-amp was "terminated" as a voltage follower from the ouput of the current sense amplifier.

    Juan

Offline xavier60

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Re: Linear lab power supply
« Reply #330 on: January 20, 2019, 11:32:53 pm »
 Single stage filters aren't really good enough. Not just because of the poor theoretical performance, PWM signal can leak past the capacitor's parasitic resistance and inductance.
A double stage filter can give much better filtering without causing the voltage and current settings to be too sluggish.
 http://sim.okawa-denshi.jp/en/CRCRtool.php
4.7K, 1uF,33K and 100nF give a good result.

EXTRA: or double up the existing parts, 10K, 1uF, 10K and 1uF. The settling time is still short enough.
« Last Edit: January 21, 2019, 12:42:04 am by xavier60 »
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Offline JuanGgTopic starter

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Re: Linear lab power supply
« Reply #331 on: January 21, 2019, 04:52:07 pm »
Single stage filters aren't really good enough. Not just because of the poor theoretical performance, PWM signal can leak past the capacitor's parasitic resistance and inductance.
A double stage filter can give much better filtering without causing the voltage and current settings to be too sluggish.
 http://sim.okawa-denshi.jp/en/CRCRtool.php
4.7K, 1uF,33K and 100nF give a good result.

EXTRA: or double up the existing parts, 10K, 1uF, 10K and 1uF. The settling time is still short enough.

I added the second stage to the filters Component values can be changed anytime. I have also consolidated some drill sizes and labeled functional blocks.
    Juan
« Last Edit: January 21, 2019, 04:56:23 pm by JuanGg »
 

Offline xavier60

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Re: Linear lab power supply
« Reply #332 on: January 21, 2019, 09:59:33 pm »
Q5 needs C-E swapped.
R32 no longer has a clear benefit.`It was originally meant to break up a loop formed between bypass capacitors on the rail between two separate areas of the board.
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Offline JuanGgTopic starter

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Re: Linear lab power supply
« Reply #333 on: January 21, 2019, 10:10:14 pm »
Alright, thanks for spotting that. I'll make those changes and hopefully order tomorrow or the following day, as most prototype services in China close for the Chinese new year and I want to get this thing made sooner than later. I'll do some more testing on the current sense amplifier if I'm able to.
    Juan

Offline JuanGgTopic starter

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Re: Linear lab power supply
« Reply #334 on: January 22, 2019, 03:31:22 pm »
Attached is the final PCB and the revised schematics. I hope everything is ok. I'll order this afternoon.
    Juan
« Last Edit: January 22, 2019, 03:35:34 pm by JuanGg »
 

Offline JuanGgTopic starter

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Re: Linear lab power supply
« Reply #335 on: January 22, 2019, 05:23:54 pm »
Just ordered 10 of them (for the same price as 5 ?) and a couple spare components. About 1 € each board including shipping. Really cheap. Let's see how it goes.
    Juan

Offline xavier60

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Re: Linear lab power supply
« Reply #336 on: January 22, 2019, 08:35:56 pm »
We didn't discuss on/off control. Ill be turning off the reference voltage to the Pots.
I guess that you could do the same sort of thing. The filters will make the rise and fall times a little slow,shouldn't be a problem in practice.
« Last Edit: January 26, 2019, 12:30:02 am by xavier60 »
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Offline JuanGgTopic starter

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Re: Linear lab power supply
« Reply #337 on: January 22, 2019, 09:05:27 pm »
We didn't discuss on/off control. Ill be turning off the reference voltage to the Pots.
I guess that you could do the same sort of thing. The filers will make the rise and fall times a little slow,shouldn't be a problem in practice.
That is what I had thought, just turning off the PWM. Rise and fall times won't be significant for manual operation I think. I can always add a hard switch that completely disconnects the output if needed.
    Juan

Offline JuanGgTopic starter

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Re: Linear lab power supply
« Reply #338 on: January 22, 2019, 10:27:45 pm »
I just realized I designed the current sense amplifier to give a maximum of 1.1 V in order to use the 1.1 V Arduino ADC internal reference, and tapped off the voltage feedback divider to measure voltage, which gives a maximum of 5 V  :palm:. I'll just increase the gain of the current sense amplifier to give 5 V out at full current, and use the 5 V rail as a reference (perhaps less precise, but I am using it for the PWM anyway) Fortunately, it can be easily fixed and PCB remains the same. I hope I haven't messed up anything else.
    Juan
« Last Edit: January 22, 2019, 10:29:48 pm by JuanGg »
 

Offline JuanGgTopic starter

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Re: Linear lab power supply
« Reply #339 on: January 24, 2019, 05:10:39 pm »
PCBs have got manufactured without any problems and have already been shipped. I will get them in a couple weeks. Meanwhile, I'll work on the software if I have time.
     Juan
« Last Edit: January 24, 2019, 05:49:29 pm by JuanGg »
 

Offline JuanGgTopic starter

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Re: Linear lab power supply
« Reply #340 on: February 07, 2019, 06:55:54 pm »
I have just received the PCBs and some misc components. They look fine as far as I can tell. Attached is a photo of the front, back and one with the big components fitted just for testing. I am not too happy about the PWM filter capacitors covering the Arduino's USB port, and the film ones that I ordered have too big footprints. I'll have to take the arduino out to program it anyways, so the serial comunications don't interfere.
I'll assemble it this weekend and see how it goes.
    Juan

Offline JuanGgTopic starter

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Re: Linear lab power supply
« Reply #341 on: February 08, 2019, 06:56:50 pm »
R8 and R16 (on my schematics) are 10 M. I don't happen to have resistors that high around. I'll have to order some. I assume they can't be 1 M or so (which is the highest I've got). I'll solder just the CV loop for now.
    Juan

Offline xavier60

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Re: Linear lab power supply
« Reply #342 on: February 08, 2019, 09:40:18 pm »
Don't fit R16, it might not be needed for your op-amp anyway.
Changing R8 to 1MΩ shouldn't cause a noticeable problem. We can check that later.
R17 needs to be recalculated depending on what current range you are aiming for.
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Offline JuanGgTopic starter

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Re: Linear lab power supply
« Reply #343 on: February 08, 2019, 11:13:47 pm »
Ok. I'll do just that. I have soldered the CV loop and it seems to work just fine from the PWM. I have to do further testing. I had to parallel/series a couple resistors in order  to get values I didn't have around. Film capacitors clear the USB port no problem.
Hopefully tomorrow I'll try the CC out.
I am aiming for 0.5 A max output current.
    Juan
« Last Edit: February 08, 2019, 11:18:31 pm by JuanGg »
 

Offline JuanGgTopic starter

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Re: Linear lab power supply
« Reply #344 on: February 19, 2019, 04:38:31 pm »
Sorry for not posting in a while. I've been busy.

I have got the code working to a usable extent, and the CV loop works fine controlled from the micro. I can set the voltage/current with the encoder and show the measured values on the displays

Don't fit R16, it might not be needed for your op-amp anyway.
Changing R8 to 1MΩ shouldn't cause a noticeable problem. We can check that later.
R17 needs to be recalculated depending on what current range you are aiming for.

So do I just put a jumper where R16 was?
How is R17 calculated? I don't really understand how the circuitry around the CC op-amp works. Thank you.
    Juan

Offline xavier60

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Re: Linear lab power supply
« Reply #345 on: February 19, 2019, 05:02:57 pm »
Sorry for not posting in a while. I've been busy.

I have got the code working to a usable extent, and the CV loop works fine controlled from the micro. I can set the voltage/current with the encoder and show the measured values on the displays

Don't fit R16, it might not be needed for your op-amp anyway.
Changing R8 to 1MΩ shouldn't cause a noticeable problem. We can check that later.
R17 needs to be recalculated depending on what current range you are aiming for.

So do I just put a jumper where R16 was?
How is R17 calculated? I don't really understand how the circuitry around the CC op-amp works. Thank you.
    Juan
R16 is to give the CC op-amp some positive offset if necessary. If you don't have the 10MΩ resistor, fit nothing in its position.
R17 and R15 form a divider that applies a positive voltage to the non-inverting input of the CC op-amp. R14 keeps the inverting input at 0V.
The current regulating setting is very close to the voltage applied to the non-inverting input divided by the shunt resistance.
125mV will give close to 500mA.
https://www.eevblog.com/forum/projects/linear-lab-power-supply/?action=dlattach;attach=629695

Edit: corrected "R16" to "R17" in the 2nd line.
« Last Edit: February 21, 2019, 12:02:24 am by xavier60 »
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Offline JuanGgTopic starter

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Re: Linear lab power supply
« Reply #346 on: February 19, 2019, 05:19:26 pm »
Quote
R16 is to give the CC op-amp some positive offset if necessary. If you don't have the 10MΩ resistor, fit nothing in its position.
R17 and R15 form a divider that applies a positive voltage to the non-inverting input of the CC op-amp. R14 keeps the inverting input at 0V.
The current regulating setting is very close to the voltage applied to the non-inverting input divided by the shunt resistance.
125mV will give close to 500mA.

Allright, thank you.
    Juan

Offline xavier60

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Re: Linear lab power supply
« Reply #347 on: February 20, 2019, 06:16:57 am »
R16 is needed only if CC mode can't be set all the way down to zero amps.
« Last Edit: February 20, 2019, 08:30:08 am by xavier60 »
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Offline JuanGgTopic starter

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Re: Linear lab power supply
« Reply #348 on: February 20, 2019, 04:14:35 pm »
 I have tried the CC loop and it seems to work fine. I calculated R17 to be 400k. As a 470 k was already fitted I tried it temporarily with that. I'll have to do further testing and calibration and maybe add a calibration routine to the code, so I don't have to manually update the hard-coded calibration constants.
This project is taking shape, but lots of things to be done yet, including finishing the case, mounting the PCBs and adding more functionality to the code.
    Juan

Offline xavier60

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Re: Linear lab power supply
« Reply #349 on: February 20, 2019, 07:57:24 pm »
I sometimes solder in IC socket pins to where I expect to have to change component values later.
I get them from chopping up machined pin IC sockets. Or they can be bought in SIL form.
« Last Edit: February 20, 2019, 11:00:32 pm by xavier60 »
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