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Among the advantages:
-simple circuit
-requires only one magnetic component, the transformer
-easy to get multiple outputs, with relatively good crossregulation
-requires only one diode per output
-isolation is easy to achieve; due to the relatively good tracking, sometimes the feeback can be completely on the primary side, off an auxiliary winding.
Among the disadvantages:
-the transformer is larger than in a forward, for instance, for the same power
-the currents, especially output rectifier and capacitor currents get very high
-power is limited to about 150W, due to high peak currents
-due to high currents, it generates more EMI
-high output cap peak currents generate relatively large output spikes, sometimes requiring a secondary LC filter
Well, it can be pushed a little, but the real problem are the peak currents, especially in the output capacitors.
Take an example: 5V, 30A=150W. In discontinuous mode, assuming 50% duty-cycle you get peak currents of 120A!
Assuming continuous mode of operation, you reduce them to about half, but that is still 60A. And the RMS value of these currents has to be supported by the output capacitors. Not easy.
Even a 15V, 10A output still means you need 20A peak.
Of course, it can have multiple outputs, so the currents will be lower.
However, flybacks are generally limited to about 150W.
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