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Old 5th November 2002, 08:01 AM   #1
UrSv is offline UrSv  Sweden
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Default Regulated bench PSU

Hi guys,

I have been looking around the web for a long time for a schematic for a dual-rail tracking power supply. I would like it somewhat scalable and with something like 40-50 V per rail and maybe 4-5 A per rail. I want voltage adjust and current adjust so that I may run constant voltage or constant current. It would be most useful for testing my projects and may then be used from anything to a small OP-amp based pre to a power amplifier like an Aleph (and I think I have the dissipation issues resolved).

I have found nothing. Does anybody have something like this? I know Elektor has had many projects but I have none of those magazines.

Thanks/UrSv

PS. Single rail is no problem but tracking dual-rail is.
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Old 5th November 2002, 02:36 PM   #2
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not that this really helps you...
I would like to see some of the single rail designs. I know I should look it up myself but it would still be nice to see what you have found.
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Old 5th November 2002, 03:29 PM   #3
joensd is offline joensd  Germany
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Hello,
I mean the easiest test supply would be just a transformer, caps and a variac. But not everybody has this lying around.
What about a capacitance multiplier with adjustable voltage?
A lot of adjustable power supplies (single and dual rail) you can find in datasheet of for example National Semiconductor and especially Linear Technology.
The LT1038 for example would work for up to 10A but at such high currents power dissipation becomes important.
I don´t know what you are looking for Lligior but if you´re looking for an adjustable test supply (not for audio) I´d use the old-fashioned LM723. I built a few PSU´s with that chip and they´re just perfect for test/repair-purposes.

Jens
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Old 5th November 2002, 03:35 PM   #4
e96mlo is offline e96mlo  Sweden
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Try Burr-Brown's OPA548 and OPA549. They are power OP's with a current adjust pin. Very nice and easy to use.

/Marcus
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Old 5th November 2002, 07:44 PM   #5
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Default I just bought another one today

the problem of <em> make vs buy </em> -- it's cheaper to buy a used HP, Lambda or Sorensen in this range. EBay now has a power supply category -- search under Business & Industrial/Electrical Equipment. There are always a lot of low noise analog supplies.

I just bought another beefy HP supply today. One which falls within your range is the HP6129C -- actually a quasi-complementary voltage amplifier -- requires you to build a programer, but this is easy with a PIC or AVR -- here's one which I own:<p>http://www.tech-diy.com/beast.htm
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Old 5th November 2002, 08:19 PM   #6
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Not long ago i put together a low current (1.2A) dual 0-30V supply with some adjustable regulators and some salvaged panel meters. This will work for active crossevers and preamps but its not exactly a workhorse. No good for output stage testing, and it would be nice to be able to test without having a pile of xformers laying around. So my thinking is if I can set a schematic that uses at least some parts I have it might be worth it to build one. More or less a feasability study if you will.
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Old 5th November 2002, 09:25 PM   #7
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(edit time ran out)

joensd

just looked at the data sheet LT1038 seems pretty good. seems like it would be easier to use a fan on the heatsink than construct their scr efficieny circuit. May even be able to use two of them to get a current limiter too. Thanks this is almost the same circuit I just built. If only I had seen this first... but this will take some serious heatsinks. Just an oppertunity to try out to-3 package
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Old 5th November 2002, 10:19 PM   #8
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You really need to look at the diy opamps article by Nelson Pass. It has some great info on building opamps from transistors. You can use transistors as large as you need. I have built an opamp with a 1600W dissipation rating using this (and it only cost about $30).

I am also building a bench power supply. It is positve and negative 0-30V 0-10A. It uses 8 TO-3 power transistors on a huge heatsink. I have not finished it yet but what I have tested looks promising. It shouldn't be too hard to modify for your needs. In about two weeks I should be able to tell you if it works or not.

http://gemini.tntech.edu/~dlh5678/psu.html

It consists of 3 boards which have not been properly documented yet.

http://gemini.tntech.edu/~dlh5678/psupos.pdf
http://gemini.tntech.edu/~dlh5678/psuneg.pdf

This has pot connections and controls a character lcd panel displaying voltages and currents. The other boards also connect to this.
http://gemini.tntech.edu/~dlh5678/psumeter.pdf

I also considered those huge opamps. They are expensive, and would probably smoke. You could be talking about 500W-1KW dissipation at a low voltage setting.

Darrell Harmon
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Old 6th November 2002, 12:34 AM   #9
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I ran out of time on that last post because I had to go somewhere. I will try to explain more now. Don't trust the resistor values in the schematics since they are just guesses.

I am attatching schematics
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Old 6th November 2002, 12:52 AM   #10
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And now the negative supply opamp.

Don't trust the resistor values. They are best found by trial and error. Read diy opamps for an understanding of how this works.

Set the positive amp up as either a buffer of a positive gain, and set up the negative opamp as an inverting amp. I set mine up where +10V would give full scale output. I did this so I could use cheap opamps for everything else. I also added current sensing resistors and a difference amp to sense current. If current goes above the preset limit another opamp pulls down the voltage setting.

This thing will need some serious heatsinks, and probably 4 output transistors in parallel. I chose the MJ2501 because it is cheap. Mouser sells it for about $3. It is a PNP darlington in TO-3 and is rated for 200W.

Depending on resistor values this thing will have some offset and you might want to enclose it in the feedback look of another opamp.
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