# Can I give DC 12V to a AC 12V input?

I have a circuit that takes 12V AC as an input but my bench power supply only delivers 12V DC, is there any issue if I give the device DC instead of AC? (Same voltage)

Straight after the input there is a 4 diodes bridge to make it DC so I would say that it's not a problem since the current would flow only through 2 diodes instead of 4, just want to be sure.

If you have a bridge rectifier and want to feed 12VDC into it, there are a few things to consider.

In 12VAC, peak voltage would be about 17V, so whatever is after the rectifier (say a linear regulator possibly) its expecting 17V (minus diodes drop). If it is for example, a typical 7812 12V regulator, it needs at least 14V to work properly. If its a lower voltage regulator (say, unlikely 9V or 5V) it might work fine.

With AC, current flows through 4 diodes, feeding DC only uses 2. So they have to handle double the current (which may or may not be fine).

I wouldnt really recommend doing it this way. If it has a rectifier it probably uses DC somewhere down the line, and if you have a bench supply you can feed it there.

p.s.: you might want to take the precaution of disconnecting unused parts of the circuit, some regulators dont like to have voltage on their output higher than input and your circuit might not have protection for this.

p.p.s.: clarified in the comments but written here for future reference: a full bridge rectifier can give positive and negative power rails, which 12VDC do not supply.

• The only thing I have after the bridge are resistors and capacitors, no 7812 regulator. The circuit board is an amplifier. And right after the bridge I have a capacitor of 3300µF any recommandation knowing that? – rels Mar 27 '16 at 16:06
• do you know how much current it consumes? is it a preamp, power amp, headphone "amp"? can you upload a picture of it? – Wesley Lee Mar 27 '16 at 16:40
• It's a power amp, it's more or less the same as this one goodluckbuy.com/… – rels Mar 27 '16 at 16:43
• hmm most likely it will not work. It needs both a positive and a negative rail. There are single supply configurations but I don't believe this is the case. Also you would have considerably less output power due to limited supply range (probably somewhere close to 2W looking at the ICs datasheet). – Wesley Lee Mar 27 '16 at 16:56
• If you really want to use this board I would salvage a transformer from old linear PSU bricks. If you really need to use 12VDC I would recommend a Class-D (or Class-T) amp. – Wesley Lee Mar 27 '16 at 16:58