power supply for plus and minus 12 V dc from 240V ac

Thread Starter


Joined Nov 22, 2006
I am a college student need to build a power supply for my project.
The project is require the + and - 12V dc.
I need to convert the housing voltage (240V AC) to plus and minus 12V DC.
I am looking for guidance.
Can someone teach or provide me the schematic diagram on how to contruct a circuit for this power supply?


Joined Nov 1, 2006
You didn't specify whether you wanted the ±12 VDC outputs regulated or not; if you don't need regulation go with a transformer with an 18 to 20 V center-tapped secondary. If you need regulated ±12 V then get one with 24 V. Mouser Electronics [www.mouser.com] has a good assortment of transformers including some with dual primaries which operate on 120 & 240 VAC [as shown in the sketch].

The filter caps can be about 25 working volts; observe polatity when connecting them. If you want regulate the outputs connect a 7812 between the positive 12 to 17 V terminal & common, & a 7912 between the negative 12 to 17 V terminal & common.




Joined Jan 10, 2006
You also dont let us know what sort of current you want out of it.
Most kitset suppliers would have something that would do the trick for up to 1 amp. Locally, Jaycar have a + & - 15 volt supply PCB, which will do fine if you replace the 7815/7915 regulators with the 7812/7912 regs mentioned by Wire addict. A 24 - 30 volt centre tapped transformer with that modified PCB would work just fine.