Variable voltage power supply (100mA)

[hameeds01]

hey guys

i needs a variable voltage power supply (-3v to +3v) @ 100ma

Regards

 

[ucsam]

Use LM317 and some caps and variable res...it works fine.( I assume that u already have rectified output with +ve() and -ve()). and it can supply huger amount..

 

[nandhu015]

Use LM317 and some caps and variable res...it works fine.( I assume that u already have rectified output with +ve() and -ve()). and it can supply huger amount..

I think LM317 does not support -ve supply..

 

[Borber]

For 100mA you can parallel connect few ordinary operational amplifiers and use dual supply (amplifier outputs must have 10ohm series resistor) or one high current amplifier. Then you will have source/sink power supply for those -3÷+3V.

 

[ucsam]

oopps!! sry...please check me.I am very sorry.

 

[dick_freebird]

If you have power to burn, stack supplies. One fixed negative,
and a variable positive referenced to it. For instance you could
have a center tapped xfmr, bridge rect & and filter, a 7905 for
the negative and a 317 for the positive with its "ground" being
the -5V and its supply, the +raw.

But there's also the possibility that this is just a high power
op amp, and an off-the-shelf split supply.

 

[mehtadhaval]

U can use LM317 for regulating +ve voltage and LM337 for regulating -ve voltage.

 

[betwixt]

You can do it in one LM317. Decide the fixed and variable resistor values so the output voltage would be adjustable from 1.25 (which is the minimum for the LM317) to 7.25V. Now derive a 4.25V supply, if it doesn't have to be super accurate you could use a 7805 with a silicon diode in series with it's output, and use that as the ground connection. The difference between 'ground' and output is now continuously adjustable between +3V and -3V and the current rating would actually be more than 100mA,giving a wide safety margin.

Brian.

 

[Borber]

I think that +3V÷-3V power supply must have source/sink capability and this can not be realized with LM317 unless you use dummy load which will draw more current than PS is specified (100mA).

 

[betwixt]

The word 'Supply' means to make something available. I do not understand why current has to sink somewhere. Look at it in a very simplistic way: Connect a small 3V lamp across the output, if the voltage is adjusted from +3V through zero and on to -3V, all that happens is the lamp dims and lights again. Are you suggesting the lamp is producing current by itself ?

Brian.

 

[Borber]

It's throuth you do not understand. Resistive load accross the output terminals causes that at +3V current flows from A to B. At -3V it will flow from B to A. It changes it's direction. That's why in one situation terminal A sources the current and in other it must sink the current. Terminals change polarity on transit from +V to -V. Is it Clear now?

 

[erikl]

... in one situation terminal A sources the current and in other it must sink the current.

Very true, also for terminal B. "a 7805 with a silicon diode in series with it's output" would have sort of a problem with sinking ;-)
SCNR

 

[betwixt]

Sorry for my 'Senior moment', I guess it comes from getting old.

What I suggested would work fine as a voltage source but I agree, it would not handle 100mA when giving a negative output.

A solution that would work and would be simple is either a power op-amp or possibly an audio power amplifier with suitable adjustable bias point. It might even be possible to use a bridge driver circuit.

Brian.

 

[Borber]

In Elektor october issue you can find 16W audio power amplifier realized with 32xNE5532 (64 in total) opas parallely connected output stage. Parameters are excellent.