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Building a Power Supply

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I am in southern Canada, some parts of the USA are north of me. My sidewalk and road have no snow but my yard has a few inches. I was driving around town yesterday when it was snowing. Slipping and sliding all over the place was fun. I have never used snow tires.

Here is the latest schematic of the fixed power supply.
 

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My career was in analog electronics design for 35 years and the only regulated power supply I ever had or made that I rarely used is a 12V/1A one using an LM317 adjustable voltage regulator IC. Now it is used as a charger for the Lithium battery in a portable vacuum cleaner. Most of the circuits I design and use do not need a regulated power supply.

Today it is -20 degrees C (-4 degrees F) outside. It has been like this for nearly one month. This cold spell broke records going back to the 1970s. It doesn't bother me because a couple of months ago I stopped taking the medication that slowed down my heart and made me feel cold all the time. My doctor says the medication is no longer needed because I am well.
 
LE: Local Enforcement (police)? I laugh when I see them driving at night with their computer blinding them and their police car has no lights on.
When I type "I" sometimes my pc types in italics.
 
If I am typing along then I accidently clip the CTRL key with the SHIFT key like this: think that is what happens but the I is missing.
 
Hi Audio

Go to the reply box for this post and type something, then holding the Ctrl key press b then i then u and watch the tablet in the top LH corner of the reply box and you'll see what I mean .

S
 
In my schematic of the fixed power supply, notice that opamp U3 is the only one needing the -1.3V supply so that its output can go negative enough that diode D9 can reduce the output voltage to zero if the current regulator needs it at zero.
U3 does not need its output voltage to go very high so its positive supply pin is fed the unregulated positive voltage through a 10V zener diode to keep the total supply of U3 less than its maximum allowed voltage of 44V.
 
I show the few changes for the fixed circuit. Some resistors are physically larger and will not fit on the pcb. Look at the value of C1.


The original circuit had a maximum output current much higher than 3A which destroyed many parts. It also allowed the maximum output voltage to go too high so the output was not rtegulated and was full of ripple.
The new calibration trimpots are adjusted so that the maximum current is exactly 3.0A and the maximum regulated voltage is exactly 30.0V.
I remembered this circuit now that I want to add a charge pump negative bias supply to a bridge rectified supply, so came looking for it. I'd started doing my own one based on a Greinacher circuit, didn't get it quite right so this is what I need. Buuutt... what is the purpose of R2? Is it just to limit the current through the diodss, or does it serve some other purpose?
 
Thanks AG. I thought it was but wanted to a wiser head than mine to confirm it :D
 
I just ran a simulation of that little charge pump V- supply. AFAICT, it doesn't work, you're lucky to get -200mV out of it.
 
Ok solved - put a full Greinaicher on there with one side of the bridge acting as the 0v leg and you get the peak voltage available as an extra rail to play with.
 
Yeah, come across the circuit before but I only discovered the name when I was looking into this.
 
I come to this discussion exactly as Music Manager did... A novice, wanting to learn, choosing the Chinese PSU kit, thinking it was adequately engineered... discovering that the kit has problems, wanting to fix its issues, and by it all, frustrated. I have read the thread some several times, but I don't think I am following the instructions correctly...

I thought that the corrections to make the kit operational were summarized on Post #34... Accordingly, I have made those changes... However, as I look back through the thread, I think I may be seeing additionally needed changes. Audio Guru, would you please make a single, complete list and schematic for me?

I have a 24vac, single secondary transformer. It is producing ~25.5vac from 110vac/60Hz mains. That's about 32vdc, as I recall, after the rectifier.

I am shooting for 0-30vdc and 0-3amps... I ended up with multiple sets of kits, due to shipping errors. The first kit I assembled, without any changes, was producing the target numbers, but with overheating. It appears that a 28vac transformer maybe suggested...

Additionally, I will be changing the fan voltage regulator to a 7812. I have a 40mm fan and heatsinks for cooling...

The 12K cap is huge... I will bodge it onto the bottom side of the PCB...

Thank you for your help!
 
Hi T1d

Audio Guru, would you please make a single, complete list and schematic for me?

There is exactly that at post #41

I have bought the additional bits specified in AG's list, but haven't got around to building yet ... I have to say, I have been using the Chinese kit 'as is' without any problems .. although it's also true that 30vdc @ 3 amps is a rare event.

S
 
Hi AG

I'm hoping you will see this .. .. do you remember this thread from quite a while ago ?
You sent me a revised schematic and parts list for the chinese PSU kit I built which I kept with the intention of building at a later date. As you can see, a question was posted about the kit and modifications today which reminded me I must get on with building the new PSU.

I have one question .. .. .. are your modifications intended to fit onto the PCB that comes with the kit or should I look to make a new board ?

Thanks

S
 
The Chinese pcb is different to the circuit I worked on so you should make a new pcb. There are a few people who designed a pcb for my corrections in the forum at https://www.electronics-lab.com/ where the original defective Greek kit was a project.
 
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