Why is it that high frequency transformers can be smaller than their low frequency counterparts?

Question

I understand that switching power supplies (such as those used in computer power supplies) can use small, light transformers because they convert AC to DC and then convert the DC to high frequency current before stepping the voltage down through a transformer. For a given wattage power supply, a switching power supply is much smaller and lighter than than a non-swithching supply because it can use such a small transformer. Why does a high frequency allow a smaller transformer to be used?

It seems to me that for a given wattage supply, whether switching or not, the same amount of power passes through the transformer. Since only the frequency of the input voltage is changed, but not the voltage itself, the currents in the transformer's windings should also be the same for either supply type.

What is it about high frequency that allows a smaller transformer to be used?

Thanks!

Answer 1

higher frequencies( hertz) make motors and loads conusume less amps this meansa smaller transformer can provide the eame KVA if it is producing a high HZ

Answer 2

A finite time passes before magnetic saturation. It is proportional to the applied voltage as a higher voltage forces more current and the reactance is finite. So a small magnetic has to cycle faster. If it handles - for example - 1 joule and it does this 50,000 times a second there is appreciable power.
This is seen even in rotating equipment. Aircraft at 400Hz is smaller for the same power. Be it transformers or motors.

Answer 3

For the same size core which would saturate at a given number of Amp-Turns. At higher frequencies you can use fewer turns so that a higher number of Amps can be handled by the same core, given that the core and electronics can handle the higher frequency.

Another way to say the same thing is that at a higher frequency the inductance of the windings can be lower.

Answer 4

The main reason is that typically you don't need high power at high frequencies while typically low frequency devices that require a tranformer ususally need it because of high power demand.

Answer 5

Every time i ask a question, even if it's the simplest one, they cannot provide me a good informed answer on this website. What happened to people who actually make the effort to write an answer??

Answer 6

Haven't thought about that