A power supply is usually the name given to an electrical component that changes an ac voltage to a dc voltage. Power Supplies are used in electrical control circuits where certain components require a dc voltage to operate. These components can be things like proximity sensors, relays, flow meters and inputs to a PLC.
How It Works
Inside a typical power supply will be at least one diode. A diode is and electronic component that only lets current flow in one direction, that’s why it is drawn like an arrow. When an ac signal goes into the diode only the positive part of the ac wave is allowed through. Check out the image below of an ac signal going into a diode
And below is what the diode lets through.
So this has made the signal change from an alternating current (ac) to a direct current (dc).
But It’s Not A Smooth Signal
You may have noticed that the dc signal is still bumpy, well very bumpy actually. This is because inside a power supply there are usually more diodes and other electrical components like capacitors that help smooth out the bumps so the signal starts to look like this
And then ultimately like this
A completely smooth dc signal!
Some Technical Blah Blah Words
This single diode arrangement is called a half wave rectifier (because it only lets through half the ac wave). It is hard for this kind of power supply to create perfect dc without ripples (or bumps). So more complex full wave rectifier circuits are often used to give a smoother dc signal at the output.
To Recap
A power supply converts an ac signal to a dc signal, it does this by the use of electronic components called diodes.
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