Voltage Doubler

darryl_co · Mar 18, 2011

Hi,
I need a low voltage high current(6V/1A) to run a audio power amp and high voltage low current(12V/100mA) to run the control circuit from a single winding transformer wrt Gnd terminal.Using a center tap transformer would reduce the current efficiency of low voltage line.I have attached a image.Please help me!

Reloadron · Mar 18, 2011

Do you already have the transformer?

Does the voltage need to be regulated?

Ron

tcmtech · Mar 18, 2011

What do you mean by,

Using a center tap transformer would reduce the current efficiency of low voltage line.

darryl_co · Mar 18, 2011

Reloadron said:
Do you already have the transformer?

Does the voltage need to be regulated?

Ron

I do not have the transformer but I want to use standard transformers available.When I mean by standard is the txs are 6-0-6 or 0-6 or 9-0-9 or 0-9 not 6-0-9 or 0-6-9.The high voltage will be fed to the input of 7812 regulator.

darryl_co · Mar 18, 2011

tcmtech said:
What do you mean by,

If I use a 6-0-6/1Amp (A-B-C)volts tx and wire it as a bridge between A and B and maybe a diode from C (half wave) i would not get the full current capacity of the tx

Reloadron · Mar 18, 2011

darryl_co said:
If I use a 6-0-6/1Amp (A-B-C)volts tx and wire it as a bridge between A and B and maybe a diode from C (half wave) i would not get the full current capacity of the tx

So use a 2 amp 12V CT transformer. Pretty common and available at Radio Shack it is so common if I am not mistaken. Do you need regulated voltage?

Ron

Diver300 · Mar 18, 2011

I had a similar problem (more years ago than I care to mention).

I used this circuit:- Voltage doubler - Wikipedia, the free encyclopedia

You can reduce the ripple by having that circuit twice, once from each leg of the 6-0-6 transformer. The two instances share the same output capacitor.

Alternatively, you could use a boost regulator from the 6 V circuit.

darryl_co · Mar 18, 2011

Reloadron said:
So use a 2 amp 12V CT transformer. Pretty common and available at Radio Shack it is so common if I am not mistaken. Do you need regulated voltage?

Ron

"2 amp 12V CT transformer" Do you mean 12-0-12(24V) or 6-0-6(0-6-12) 12v? Either ways what is the schematic? As already stated the high voltage i.e goes to the input of a 7812 voltage regulator and the low voltage just need to be full wave rectified and filtered as its for a power amp,regulation not required

Driver300 - "I used this circuit:- Voltage doubler - Wikipedia, the free encyclopedia" It seems to be a half wave voltage doubler thus reducing the output current

Diver300 · Mar 19, 2011

darryl_co said:
Driver300 - "I used this circuit:- Voltage doubler - Wikipedia, the free encyclopedia" It seems to be a half wave voltage doubler thus reducing the output current

Any voltage doubler will halve output current.

The circuit is a half-waver doubler. That is why I suggested having the circuit twice.

audioguru · Mar 19, 2011

A single-ended audio amp using only 6VDC for its power supply has an output at clipping of only 0.26W into 8 ohms which is almost nothing. Two amps produce 0.52W of sound plus about 0.35W of heat for a total power of 0.87W. It draws 145mA from 6VDC when both channels are at clipping. The transformer must supply 1.2W at 6VAC.

If the amp is bridged and the stereo speakers are 4 ohms each then the output at clipping per channel is about 0.9W. The total power would be 1.5W from 6VDC and would be 2.1W from the 6VAC transformer.

tcmtech · Mar 19, 2011

I don't see why you don't just use a center tapped 6 -0 - 6 transformer with a full wave bridge between the ends and use the center tap as your 6 volt source. No efficiency or power handling capacity of the transformer is lost either.

Reloadron · Mar 19, 2011

tcmtech said:
I don't see why you don't just use a center tapped 6 -0 - 6 transformer with a full wave bridge between the ends and use the center tap as your 6 volt source. No efficiency or power handling capacity of the transformer is lost either.

That is what I was suggesting. Use a 6-0-6 transformer (12 Volts CT) with a bridge and use the CT for your 6 volts.

Ron

audioguru · Mar 19, 2011

But I betcha he wants to connect the ground of the 6VDC to the ground of the 12VDC.

4pyros · Mar 19, 2011

A 6 volt audio power amp, whats that from a boom box? Use or make a 12 volt amp.

Reloadron · Mar 20, 2011

audioguru said:
But I betcha he wants to connect the ground of the 6VDC to the ground of the 12VDC.

Uh Oh, never thought about the common ground thing. Good point AG.

Ron

darryl_co · Mar 20, 2011

Thats right, i wants to connect the ground of the 6VDC to the ground of the 12VDC

tcmtech · Mar 20, 2011

But I betcha he wants to connect the ground of the 6VDC to the ground of the 12VDC.

I still don't see where thats a problem using the center tapped transformer and full wave bridge rectifier concept.

audioguru · Mar 20, 2011

tcmtech said:
I still don't see where thats a problem using the center tapped transformer and full wave bridge rectifier concept.

It makes +6v and -6V. Its 12V is the total of both without connecting to the grounded center-tap.

MikeMl · Mar 20, 2011

Naw:

I think this is what he wants:

Note the ripple as a function of the load currents.

tcmtech · Mar 20, 2011

It makes +6v and -6V. Its 12V is the total of both without connecting to the grounded center-tap.

So what law of physics says you cant use the -6 volt point as the common ground and the center tap as the +6 and the top end as the +12?

The transformer doesn't care about what is used for what reference point and the circuit will still see a +6 and a +12 as it needs to.

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