Electronics > Projects, Designs, and Technical Stuff
Lab Power Supply - The Lost Current
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C:

Google
  find a model number for an HP supply and find the manual using google.
As I said most are fantastic with everything. Was common in 80's to have everything in manual so user could repair it if necessary.

One thing you will find is that controlled power up and down is built in to design not a tack on.

Little things are included in a great design.   You might design the voltage control pot to change from 0 to Vref. A pot failure becomes 0 a normal setting.
The great design can have a 0 output of supply equal some %  not 0 of reference. A pot failure becomes something not normal and electronics can detect problem and shut down power supply with an error. That analog OR lets you have many circuits that can shutdown supply.

So google and study a HP supply and see what is missing in the simple hacks.  Manual not schematic as it's in manual.

The problem with a supply is often not the DC it's the load caused AC changes causing the power supply to fail. It really takes some fancy test equipment to check the AC part.

One thing some forget is what a power supply is. Most are crippled power op amps. Think it through If you had an op amp that could do X amps with a range of Y volts you have a power supply. Removing half of op amp's power stage is a cost & heat savings. The better lab supplies still have some sink capability.
Think of what a direct coupled audio amp is. Could be thought of as a bidirectional power supply.

So You have a transformer, what are the spec's, Just one winding?

Old school is using pot's to set things, New is using DAC's. Would be good to design so that ether can be used. Some were controlled by resistor decades.

Keep your eyes open. In first schematic you posted, you had Q4 as an NPN. A change to a PNP  would have let you have a supply to limits of the 2N3055 while having lower voltage control circuit.

6227B Power Supply
https://literature.cdn.keysight.com/litweb/pdf/06227-90001.pdf?id=734411
DC Power Supplies - Discontinued and Obsolete Products
https://www.keysight.com/en/pc-1000002054%3Aepsg%3Apgr/dc-power-supplies-discontinued-and-obsolete-products?nid=-536902299.0.00&cc=US&lc=eng


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xavier60:
Most of us would agree that for this type of PSU project that the topology that has everything referenced to the +out is a good starting point. The rest is details, not all will be trivial ones.
radoczi94, at the heart of understanding what is going on, it is essential that you understand op-amps. Do you understand how op-amps function and how they are applied?
I'm planning on doing some related experiments shortly.
radoczi94:
The various protection circuits are neccessary for shure. One thing I already did, is a switch-on delay with a 555 and a relay switching the output. It works, but yeah, switch contacts doesn't really like switching DC. There could be a switch-off circuit too, like in the Electronics-Lab design, monitoring the AC, even on the mains side trough an optocoupler and then connecting to the OR gate. Or even a thermal shutdown (I don't think that this is absolutely necessary in my case.)

But I can throw all the protection to the trash can if the 2 main function doesn't work. Since I do not have a scope (yet), what I can do now is just sit down and learn as much as I can. And maybe search for more suitable parts, do some sketches, collect ideas.

That massive transformer is 250VA 2X(0-3-12-24V)*5A. For this thing, 4A output current would be comfortable at 25V output. Could have an automated tap selector circuit. At least for the 12V tap. I think the heatsink could handle it either way, but why piss away 100W?

What i know about opamps...well, basics. Understood the DC operation well, and some of the AC. I found a lot of informative stuff on the Analog Devices website, there is a lot of useful stuff. I'm reading those, also found some Linear stuff about undesirable oscillations.
xavier60:
Just because a PSU has CC, doesn't really mean that it's short circuit protected. Even my Agilent U8002A will supply over 20 amps into a sub ohm load for 100us before it begins to sluggishly current limit.
I mocked up a CV/CC regulator to experiment with the CC response. The cause of the delayed CC response was because the output of the CC op-amp normally sits at close to its full + rail voltage. When the PSU is suddenly overloaded, it then takes a long time for the CC op-amp's output to slew down to the point where it takes control of the Base.
One of the reasons is that the loop compensation capacitor is usually connected directly between the op-amp's output and inverting input. I have connected the capacitor to the other side of the ORing diode so that the op-amp's output can slew at its maximum rate until the ORing diode conducts.
Because the LM358 that I have used doesn't slew that fast anyway, 0.3V/us, I have put a diode and LED in its feedback path that keeps its output at 2.2v so that it doesn't have far to swing down to take control of the Base. I am ordering some faster NE5532 op-amps to see if I can omit this extra complication.

Extra: I have used an LED for the CC ORing diode to give CC indication.
xavier60:
The 13V rails in my regulator experiment are supplied from 2 regulated  plug packs. I noticed that the regulator's output would pulse to full voltage when I powered down the plug packs only. I have added protection to prevent this from happening. Q3 cuts Base drive current when the +/-13v rails drop by a few volts.
It was also an ideal place to add an on/off switch.
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