Electronics4you

Hi there,

I want to build my own power supply. It has the following data:
Power: Max 300VA
Current: Max 10A
Voltage: 0-30V

That was the simple one. Now I have a 350VA toroidal transformer, a high power bridge rectifier and some big capacitors... and then what? I can't use an LM317 as I use to do, so I need a way to scale down the voltage from the transformer, without loosing a lot of power to resistors and others.

Any surgestions or links to good power supply circuits online?

Electronics4you

Can I use MOSFET's of IGBT's to control the voltage?

dknguyen

You did not specify AC-DC, AC-AC, or DC-DC.

AC-AC is dead easy since all you need is a transformer. Anything else requires a switching supply at those power levels for efficiency (as opposed to linearily regulating everything with a transistor). Switching supplies are hard to build- best bet is to look for a switching supply control IC that connects to an external transformer and transistors from Texas INstruments or Maxim- or you could just buy a switching supply. I don't remember any 0-30V variable voltage range ICs though, but I didn't look carefully.

IGBTs are only really used for high voltages since MOSFETs have better switching characteristics (or so I'm told).

audioguru

Here is a 0-60VDC, 0-5A linear home heater that can be easily modified for 0-30VDC, 0-10A.

Attached Images

0-60V-0-5A.jpg (104.1 KB, 61 views)

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Uncle $crooge

Electronics4you

Sorry, but I can't figure out how it works at all...

The LM317L has a maximum voltage rating of 37V
Why all that MOSFETs
What does the op. amps do and the potentiometres

Roff

LOL! Much superior to the old-style, nonlinear home heaters.

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Ron

audioguru

Then learn about electronic circuits and it is easy to see how it works.

No. Its max input-output voltage rating is 40V. Here its input is 51V and its output is 25V so it has only 26v across it which is fine.

300W is a lot of heat. 60V at 5A is 300W if the output voltage is low and the current is 5A. A single Mosfet can dissipate only about 60W when it has a pretty big heatsink so 10 of them are needed.

The left opamp is the current regulator. It turns on the LED to warn that it is reducing the voltage to keep the current regulated. Pot P1 adjusts how much current.
The right opamp is the voltage regulator. Pot P2 adjusts how much voltage.

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Uncle $crooge

stevez

In any number of ARRL Handbooks is a schematic for a power supply that is relatively easy to modify for your application. It is linear with an LM723 regulator and 2N3055 power transistors. It is far from efficient or small but it is relatively uncomplicated for a power supply with similar capabilities.

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stevez

Hero999

What's the dropout voltage on that thing?

Somehow I doubt it can input 60V and output 60V.

Electronics4you,
Is your transformer centre tapped?

It would be great if it was since you could use the centre tap for the low voltage range so you won't need such a huge heat sink for the lower voltage settings.

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audioguru

I think the dropout voltage for the 0V-60V/5A power supply is next to nothing.

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Uncle $crooge

Hero999

*looks at the circuit again*

Of course, all those parallel p-channel MOSFETs will have a really low on resistance to the voltage drop will be negligible even as full current.

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