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Old 11-27-2006, 07:37 PM
kevy kevy is offline
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Default power supply for plus and minus 12 V dc from 240V ac

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?
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Old 11-28-2006, 02:02 AM
wireaddict wireaddict is offline
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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 [] 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.

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Old 11-28-2006, 09:22 AM
Gadget Gadget is offline
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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.
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