Question about flyback snubber, cascode, and 2 switch forward.

[renzen]

I have some question about flyback snubber, cascode, and 2 switch forward. My conclusion after reading lots of application notes and articles in web, 2 switch forward is the best. But I rarely see people use 2 switch forward or cascode, and most of people use snubber or just basic flyback in their circuit design.
So, when I should use snubber, cascode, 2 switch forward or just basic flyback? Because on simulation, all is working.

 

[crutschow]

Post the circuits.

 

[simonbramble]

it is a question of power. With the flyback converter, you charge up the primary, then dump the energy into the secondary, so the transformer has to store power. Because you are only inputting current into the circuit for a fraction of the switching period (during the ON time of the primary switch), you have to put more current (per Amp of output current) into the circuit. With a 2 switch forward, you are basically putting a square wave on the input (while inputting current), and at the same time a square wave appears at the output and current flows to power the load. In other words, current flows in at the same time as current flows out, so you are not storing as much energy in the transformer core, so the transformer can be smaller. Also, since current is always flowing into the circuit, your primary current is proportionally less.. With a flyback, you have a time when the current is flowing into the load (and hence not flowing into the primary), so you have to put more current into the circuit for every Amp of load current, so the primary currents are always higher in the flyback.

That said, flyback converters are generally simpler to design which is why people design flybacks. Up to about 50W, a flyback is perfectly good. Beyond that, you need to start looking at forwards and full/half bridge converters. If you want to learn more, get a book by Abraham Pressman or Keith Billings. This is the switching regulator bible

 

[dr pepper]

Hello, I think I understood your post.
Flyback smps's tend to be for smaller apps as mentioned <100w, 2 switch forwards I've seen used in high power apps such as weld sets.