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12v and 5v Power Supply from 240v Answered

I am creating a home automation device that uses an arduino. The devices are connected to a relay. The real problem is I am using a using a DTMF decoder with the relay, while the relay works only with 12v power supply the DTMF decoder works only on 5v input (USB from computer to arduino).

The devices that I know of are capable of converting a 240 v to 12v or 5v not both.
What should be done so that I am able to get a 12v and a 5v from a normal 240v household power socket?



Best Answer 2 years ago

ATX power supplies are good, and supply (I think) +12V, -12V, 5V, and 3.3V. Without knowing current requirements, you can probably use just about any power 12V adaptor, and use a 5V buck converter to get a 5V signal. In both those cases take note that the grounds of the 5V and 12V are commoned together. They are not isolated. For that either separate 5V and 12V supplies, or a galvanically isolated DC to DC converter ($$$).

Linear or unregulated power supplies may work better for things that are electrically "crude" (like cheap DC motors producing EMI, or things that draw large inrush currents, etc.) As switchmode regulated supplies are a bit more sensitive to inrush spikes and small overload conditions. So an old fashioned clunky heavy wall adaptor may be better suited. I had a friend who could not get servos to work properly on a 5V 15A power supply, even though they worked fine on crappy 5V 1A linear bench supply. Turned out to be current transients tripping a overcurrent protection in the 15A supply.

ATX Computer Power Supply

By far the easiest and most common source of DC 12 volts and 5 volts at reasonable currents is a PC power supply.

There are lots of Instructables that tell you how to make them work and you should be able find one for nothing.

Actually this device will be coupled with our everyday switch boards so I cannot rely on a PC for power so is there any other alternatives??