Electronics > Projects, Designs, and Technical Stuff
Power Supply Design : Questions about Dual Supply and Transformer
LittleRain:
I just designed a switching PSU that converts 120V AC to 42V DC, and is capable of 20amps.
Just realized I need to create a dual supply for an audio amp I am creating, so I want to convert my single supply design into a dual supply.
Every dual supply schematic I look at, the common ground is connected to the center tap of the transformer.
But my single supply PSU does not have a transformer on the high voltage side, so I'm just wondering,
where would the common ground point even be, and is it even possible to create a dual supply without a transformer?
Do I need to add a transformer, or a second bridge rectifier, for a dual supply? I was trying to draw something up with a second bridge, but I just don't see how I would do it.
Or could I just invert the voltage after the buck converter/capacitance multiplier?
I would add a transformer, if I could find one that can do 20 amps on the secondary, but they are all like $100, unless its only 12V.
On aliexpress they sell a +/-35V dual PSU for around $50 CAD, so I know its possibly to make it fairly cheap, but I'm just not seeing how right now.
So if anyone has a transformer recommendation it would be very much appreciated. It needs to be 120V(or 120/240) on the primary, and be at least 40/42v 20a on the secondary(or should it be 90, with a center tap?).
If anyone can push me in the right direction, that would also be greatly appreciated.
I just feel like I'm missing something, and I really don't want to have to buy the one on ali just to figure it out...
Oh and as for adding an inverted buck converter, how do I make an inverted capacitance multiplier with a mosfet, would I use a P-channel?
My single supply uses a darlington for its capacitance multiplier, but finding a BJT capable of 480 watts is tricky, so for the dual supply design, I'm going to change it to a mosfet.
Thanks for any help you can provide.
MosherIV:
Hi
Can you tell us what specification you want this psu to be?
Your post was not clear what voltage and current capability the 2nd voltage rail needs to be.
From your post, it sounds like you have only found designs for dual rail linear psu.
That is why they all use transformers.
A mains based switch mode power supply will still use a transformer for isolation.
The transformer will be for high freq (probably 35KHz or higher) and probably custom made.
My understanding for multiple output supplies, is that one rail (primary) will be used to control the freq or pulse width for the transformer. Other rails will just be buck converters running off the primary rail.
LittleRain:
Hi Mosher,
Thanks for the reply.
So my dual supply needs to 480watts, +/-42V DC, 20amps from +42 to 0.
Not entirely sure how you would rate amperage for a dual supply.
The dual PSU I'm looking at is this one.
It says its a switching supply, and it has 2 transformers on it. Small one of course would be for the PWM generation, and then not entirely sure how the large one is used.
I was thinking of purchasing a core and wiring the transformer myself, but not confident that I would be able to do that correctly.
Thanks again.
Edit: Actually I probably only need something like 10A per rail, the audio amplifier I'm designing this for can use 12 amps per channel, but that's before I realized it wasn't 0 to +42, and is actually -42 to +42.
MosherIV:
Hi
So you want
+42V 20A
-42V 20A
I do not think there are 2 transformers on that smps, one of them looks like a choke/inductor to surpress emc.
Since you want symetrical rails and since it is audio, it is much easier. The load on positive and negative should be symetrical (unless you have some wired waveform that has more positive or negative half).
If the transformer is wound symetrically, you pretty much only have to regulate on rail and the other rail will track but in other polarity.
Yes, you will have to join the 2 transformer outputs in series to get the opposite polarity voltage.
Benta:
--- Quote from: LittleRain on August 17, 2020, 10:02:16 pm ---
The dual PSU I'm looking at is this one.
It says its a switching supply, and it has 2 transformers on it. Small one of course would be for the PWM generation, and then not entirely sure how the large one is used.
--- End quote ---
That's the most horrendous POS I've ever seen, and I've seen quite a bit. But OK, it's your money and your (and probably your family's) life.
Can it get cheap enough?
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