Computer Power Supply

Thread Starter


Joined Aug 19, 2009
What are the inductors used for in computer power supplies... And how do computer power supply step down voltages? Does it go straight to the voltage regulators without stepping down? (cause I don't see a transformer especially one that should hold 500W)


Joined Apr 18, 2009
The ATX power supplies rectify directly from the mains. It is a switch mode power supply (google it if you dont know what it is).

They use a transformer to achieve multiple outputs at different voltage levels. (the voltages are determined usually by the number of turns on each transformer tap compared to the primary turn count). Keep in mind that they dont use the conventional laminated iron core transformers.
Since the waveform over the transformers is in the kilohertz range they can reduce the transformer's size quite alot compared to iron core transformers at these power levels (capacitive and inductive components can be reduced in size as the frequency increases for the same power level). The main's power line (mains frequency is 50 Hz) is rectified and chopped down into square waves with frequency in the kilohertz range, perhaps 20-200kHz).

The voltage is usually regulated with low ESR capacitor filters at each output. (voltage ripple is mostly determined by the output filter capacitor's ESR for switch mode power supplies).
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Joined Feb 4, 2008
Have a look at switched mode power supplies and you will understand the basic operation.


Joined Mar 24, 2008
Switched Mode Power Supplies are ususally referred to as SMPS. I mention this because it is the normal acronym you see for them. There is a lot of good literature on the web concerning this kind of power supply. Because it is fundimentally digital in nature, it is much more efficient than older analog designs, and also noisier as a design tradeoff.
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Joined Aug 27, 2009
If it has multiple transformers, can you some how wire up a test board that would allow you to use the different volts outputs? For example 48v,24v and 12v ?