Hello everyone. I'm trying to build a switching power supply that uses a single transformer (one primary and four secondary) to produce the following output voltages: 5V, 9V, 12V, 24V; a minimum current of 5A and a maximum output current of 20A.
Could you provide me with a document that would be useful for building this power supply?

 

Building a high power switch mode supply is not a trivial matter, and not something I would recommend doing unless you have a very good background in electronics.
And I think it would be better to start with a commercial supply, maybe one for each voltage. Or use a PC power supply and an extra 24V one.
That said, do you need all the voltages to be capable of 20Amps? If so, that is a pretty large supply!

 

Here's an interesting read:

https://www.analog.com/media/en/technical-documentation/application-notes/an30fa.pdf

 

I'm trying to build a switching power supply that uses a single transformer (one primary and four secondary) to produce the following output voltages: 5V, 9V, 12V, 24V; a minimum current of 5A and a maximum output current of 20A.

Are you sure you mean a switching power supply?

I've been doing electronics as a hobby for nearly 50 years. Aside from computer supplies, I don't have any that provide more than 6A.

 

You COULD create an inverter type switcher but with only one thing to control (the inverter) only one voltage would be directly regulated. The other voltages can be regulated, I think, with "simple" PWM switching of the rectifying of the inverter AC output. BUT it would be rather complicated. And I would not try it, although in theory it can be done.