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If the second stage uses the forward converter bridge topology, it will require four mosfets, and the gates of the upper two will need isolated gate drive. The simplest solution to that is a pulse transformer, which can also drive the lower mosfet pair.Warpspeed, I appreciated your comprehensive sharing greatly. Your idea is amazing but the cost would be much higher. and the size would be another problem. It is hard to MP. another two question, 1) why does it require four isolated gate drivers? 2) how about the load regulation for the open-loop full bridge?
Flyback is uniquely suited to large ranges of Vin/Vout, and other topologies will require a larger duty cycle variation to cover the same range. This is one of the reasons it's used for universal AC-DC converters and benchtop supplies.mtwieg, thanks a lot for your suggestion. It is hard to make it with flyback because of its 72W and 1:4 input voltage. do you think it is easier than forward and push pull?
Yes its a very practical and popular topology for low and medium power direct off line power supplies.This is one of the reasons it's used for universal AC-DC converters and benchtop supplies.
BradtheRad, many thanks for your kind reminding. I agreed with your analysis. but the full H-bridge seems more complicated. can you recommend any IC to make it? I want to evaluate its complexity from the typical schematic.
Things are not completely different.Here we have 9v to 36v input dc. Ten amps input, with 40 amps at the peak of the primary. Conduction loss is I squared R so its not ten times but 100 times as difficult to deal with.
And remember we are talking about the exact same power level.
Things are very different when selecting the most suitable topology for either high or low voltages.
The only problem with keeping CCM is to design sufficient flyback transformer inductivity. Any other topology e.g. boost converter will face the same problem in some way.and then the duty cycle variation would be problem if the switching frequency is constant
I'm referring to well-known standard topologyi do not understand a PSB with secondary storage inductor
Only for buck-derived converters. For a buckboost derived converter, like the flyback, the duty cycle variation is less (assuming CCM). For example, a buck derived converter with duty cycle range 0.2-0.8 gives gain range between 0.2-0.8 gain range, while a flyback will give a range of 0.25-4, a factor four improvement in the ratio.Things are not completely different.
First point to consider is that any variable voltage ratio converter topology will somehow suffer from the 1:4 duty cycle variation, as long as it doesn't implement switched transformer taps or similar structure switching.
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