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# 0-60V 3A Dual Rail Bench Supply

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#### Raymond Heath

##### New Member
I'm attempting to build a +/- 0-60V 3A bench power supply using a Large 10 amp transformer out of an old audio amplifier. I got as far as building and testing the rectifier/filter board for +/- 60VDC and then discovered that I can't find any variable supply circuits that will take 60VDC input. I know there are old transister circuits out there, but darned if I can track one down. Any ideas?

Hi Raymond, welcome to ETO!
+/- 0 to 60V is a very big stretch, especially if it needs to supply 3A all the way down to it's lowest setting.
You mention 0-60 in terms of output, but then mention a 60v input! So what do you really have? You need a few volts overhead so if you want 60V out you probably need 65vdc in, then at a low voltage like 5v you are looking at 3A * 60V = 180W dissipation in the regulator. Which isn't impossible, just very very impractical. And wasteful.

(edit) If you measured the transformer's output with no load you are onto a red herring with the voltage. Load it with something that will draw an amp or two and test the voltage like that.

So I suggest you look at using a buck converter to drop the voltage down to a sensible level, it's a good idea to make it track the output so the voltage across the linear regulator is always the same. There are a couple of designs you can use for this.

I've seen another design on the 'net which used a chopper circuit to reduce the voltage by pwm, which you could also consider.

If you're lucky enough that your transformer has taps for other voltages you could come up with a switching arrangement to change between these.

That must have been quite a beefy amp to need such a big transformer!

You are correct, I have +/- 60VDC on the output of the rectifier/filter board. The input from the transformer is 47-0-47AC. I just re-measured everything to be sure. My filter uses a 10A bridge, two 250VDC 2200uf electrolytic caps and two 300V 473nf caps. There are two 5.1K 2W resistors on the outputs for bleeders. My original idea was to emulate something similar to my old Lambda 0-50VDC bench supply, only in two rail. I assumed a voltage drop under load. The transformer windings for that part are 20ga and the other two windings are 26ga without the enamal, one 16-0-16 and the other 9.5VAC. The transformer weighs about 5.5 lbs, it's beefy!

No such thing as 473nF cap! 473 = 47nF!
Is this the original rectifier/ smoother from the amp that you are using then? 26ga sounds a bit thin. Handy auxiliary supply though!
When you put "10A transformer" in your original post, may I ask what the 10A is derived from?
I built a similar bench PSU based on an old HiFi traffo (smaller than yours) some time ago (actually still not complete since 3 years now!) So I learned a lot from that

47nf, correct. my mistake. I appear to be in the wrong group. probably the ham group would be helpful. Thanks for your time

For a 60 V linear supply, there are very few opamps that will run directly off the bulk supply voltage. One way is to find an all discrete schematic and scale up the parts with 80 V transistors.

Another approach is to regulate the 60 V down to 15 V or so at a low current, to power the regulator circuits. This can be a very simple zener diode plus pass transistor circuit.

The first schematic above is not the best for your application because it has a fixed reference and variable feedback. For a wide range output, better to use a main regulator topology that has a fixed forward gain and a variable control input from the voltage reference. This makes for a fixed feedback resistor ratio. The only part of the circuit that sees the full 60 V is the main output pass transistor (s) and the driver transistor.

Here is an odd duck based on the National LM10.

What zero-to-full-load regulator accuracy are you trying for?

Is current limiting a requirement?

Search for Lab Supply Schematic to see many more examples.

ak

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You can get an MC1466L Integrated Circuit from China, that will do what you want.
Or you can make that IC using discrete parts.
http://chemelec.com/Projects/MC1466/MC1466.htm

This supply is Adjustable down to Zero volts and has an Adjustable Current control.

My supply is a Dual Supply with Two separate power Transformers.
So I can Series or Parallel them.
I use 10 turn Pots for both Voltage and Current Controls

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