5 V DC power source from mains with several outputs?

[adevonpo]

Hello everyone,

For a project I'm working on, I need to deliver 5 V DC to a circuit board as well as a decent amount of power (near mains voltage & current would be ideal) to a heating element. I'd like to be able to supply power to both the board and the element from a single mains connection, but I'm not sure how this would be done. Does anybody have any ideas for how to do it? My apologies if it seems like a strange or vague request, I'm very much a novice where circuitry is concerned. Let me know if I need to be more specific. Thanks very much!

 

[crutschow]

You use a transformer isolated power supply from the mains to generate the 5VDC (such as a wall-wort supply). The heater, powered directly from the mains, can be controlled with a relay (mechanical or solid-state) to provide isolation for that.

 

[tgootee]

if you are "very much a novice", then you should probably not be designing or building any mains-powered devices. If it's not done well-enough, it could electrocute you, or someone else, or start a fire. As a Scottish pipe-maker I knew once said, "Electricity is nice but don't get any on you.".

What are the requirements for the 5 VDC? i.e. What are the upper and lower acceptable voltage limits, and the maximum current that could be needed?

Typically, if doing it "from scratch", you could use a small transformer to get something a little higher than five volts peak, and then rectify the transformer's output to make it unipolar, then feed that to a reservoir capacitance, then optionally feed that through a three-terminal voltage regulator, then to your load (your circuit). The required reservoir capacitance would depend on the maximum load current and the minimum allowable voltage.

If you can discover the maximum current requirement for the 5-volt supply, then you could either buy a 5-Volt "wall wart" supply rated for at least that much current, or, if regulation is needed, buy a 9-Volt wall wart and have a 5-Volt regulator circuit where the power enters the board.