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Old 2nd January 2007, 11:09 AM   #1
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Default +/- bench supply ideas..

Hey guys,

I've been thinking of building a variable regulated +/- PSU for the bench,it could come in handy for building/testing SS amps.
I've got a couple ~300W power trannies,the DC rails were in the +/- 70-80V IIRC,so I've got plenty of raw voltage to work with. (one has a pair of lower voltage taps I could use too.) Both trannies are in the 5-10Amp range.


I've got some diodes,and filter caps,and I was thinking of using some MJE15011 and MJE15012's as the pass transistors (maybe a pair per rail) Might as well use up some of the stuff in the junkbox.


Basically I'm looking for a regulator circuit which is:
-Adjustable 0 to ~70V output. (even say 25 to 70V would be okay)
-Capable of handling say 10A continous.

Any suggestions for circuits,etc?
I've searched and stuff and can't seem to find anything in this power range..(except capacitance multiplier circuits)

I'm eye-ing an old Sansui 7000 chassis..I might build it all into that..(got some decent heatsinks on it.)
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Old 2nd January 2007, 11:28 AM   #2
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Look for a lower voltage one EXP. 0-15 and mod it for 0-70 or more, all you have to do is get a big heatsink or fan cool and parallel a several transistors to get you current rating.

BTW did you search here? I'm always seeing adjustable psu schematics on here.
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Old 2nd January 2007, 02:54 PM   #3
simingx is offline simingx  Singapore
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This may be obvious, but at those supply voltages, I hope you don't have to output too low supply voltages at high currents... even with 10V output, that means losing 60V across the pass transistors. At even 5 amps output, that's 300W... per rail! Anyone needs a space heater?

You might have to use a (tracking) preregulator to keep dissipation under control.
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Old 2nd January 2007, 06:22 PM   #4
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Yea,I had thought about that just after I posted. Yikes!

The one transformer does have taps at 25Vac or so,So I could make it switchable from 0-25V and 25-70V in two ranges.That way the transistors wouldn't have to dissipate as much power at lower output voltages..

Hmm..
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Old 2nd January 2007, 07:17 PM   #5
paulb is offline paulb  Canada
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Can the transformer be wired for 120 or 240 volts? If so, there's one way of getting a lower voltage range - switch the transformer to a 240V input but run it at 120V.
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Old 2nd January 2007, 10:19 PM   #6
simingx is offline simingx  Singapore
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Quote:
Originally posted by DigitalJunkie
Yea,I had thought about that just after I posted. Yikes!

The one transformer does have taps at 25Vac or so,So I could make it switchable from 0-25V and 25-70V in two ranges.That way the transistors wouldn't have to dissipate as much power at lower output voltages..

Hmm..

Yes that's possible. In fact some "lab" power supplies also use this method of switching between taps to keep the dissipation under control.
You will probably need an auxiliary supply for the control circuits though, if you decide on this route.
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Old 3rd January 2007, 08:27 PM   #7
KISS is offline KISS  United States
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Why not go simple: One box. AC current metering. AC voltage metering. Variac input with external isolation transformer. Standard +-V power supply bridge. DC voltage and current meters for rails.

Create a control circuit which looks at the AC power in watts and use that as a settable power and/or current limit to turn the outlet (AMP) off.

So, you will have an efficient high current line regulated supply.

For my amp testing, I have an external isolation xformer connected to a variac in series with an AC voltmeter and ammete and fuse. Outputs are a binding post and a 3 prong receptcle. Since I didn't have a fully rated variac, the power switch has a center off position. Down is variac power. Up is full isolated line power.

For a variation, make the DC rail metering to be internal or external. Change the colors of the displays for the polarity of the rails.

You don't need good regualtion for this application.
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Old 3rd January 2007, 08:34 PM   #8
lineup is offline lineup  Sweden
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there are also

2 x 0-30 Volt Lab regulated supply
to buy
for not too much money

this would give a total of 60 VDC
I think they come with max 2-3 Ampere

You can get them with Analog or Digital display
Volt and Ampere meters.
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lineup
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Old 3rd January 2007, 08:51 PM   #9
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Dang,I just sold an extra variac I had on ebay too..I can use my bench variac though.
You're right,I don't need super-regulation,just the ability to vary the voltage..
Heck,a capacitance multiplier circuit would be plenty to kill any leftover ripple,etc..

Very K.I.S.S. -A fitting nick!

I like it,I might just go build it up!
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