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I'm confused: from what I understand, switching power supplies (like this one) output DC from AC input.

But if it's true, why do (most?) motherboards use several internal switching powers supplies (e.g. to output, 3.3V, 5V, 19V...) while being powered by a charger that converts AC to DC?

How could these internal switching power supply work since they are powered with DC from the charger?

(Sorry for the basic question)

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  • \$\begingroup\$ motherboards are not powered by a charger ... they are powered by a power supply \$\endgroup\$
    – jsotola
    Nov 17, 2022 at 18:22
  • \$\begingroup\$ @jsotola Do you mean that a charger is only to charge a battery? \$\endgroup\$
    – JinSnow
    Nov 18, 2022 at 13:23

2 Answers 2

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I'm confused: from what I understand, switching power supplies output DC from AC input.

Depending on the design and, the goals, a switching power supply may: -

  • Output DC from AC (off-line SMPS)
  • Output DC from DC (DC-to-DC converter)
  • Output AC from DC (power inverter)
  • Output AC from AC (cyclo-converter)

why do (most?) motherboards use several internal switching powers supplies (e.g. to output, 3.3V, 5V, 19V...) while being powered by a charger that converts AC to DC?

There's more than one way to skin a cat.

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Thanks to Andy's answer I found an answer to my question behind: why is AC rectified to DC, then converted again into AC?

the point is to control the frequency. Once you have DC power, you can pretty much drive the inverter at any frequency you want.

It is difficult to convert one frequency to another, but it is relatively easy to convert DC into any frequency you want (and to rectify AC power to DC).

Details:

Think of the inverter as a switch that reverses polarity. If on one side you have DC, then you can switch back and forth as you want. The faster you go, the higher the frequency on the output side. You can pick any frequency you want, there are no "hard" or "easy" frequencies. They try to do the same thing with AC power on the input. Unless the frequencies match up, the output will be an ugly mess. AC power is very easy to convert from one voltage to another, using a transformer. But the frequency on the input and output side of the transformer are the same.

Thanks to M Quack from the physicsforums

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