Hi
I'm looking at the MAX845 IC:
It is a push-pull forward driver for a center-tapped transformer (see page 5)
It has a flip/flop to get 50% duty cycle, but how do they prevent flux- walking? Is that only done by the on-resistance of the MOSFETs? (higher current leads to more voltage drop - regulating the flux)
Regards
Klaus
I took a quick look, and as far as I can tell it's that and the resistance of the transformer winding -- which can problem be relatively significant given the low powers involved.
Pretty much. A way to really combat staircase saturation would be current mode control like on this one:
But usually it's not a huge problem. If EMI is an issue this converter might need a small inductor after the output rectifier. Also, the transformer should be able to handle a small DC load caused by stuff like not quite equal diodes etc. Sometimes people use airgapped cores but I never had to on forward converters.
The break-before-make action guarantees about 200nS of dead-time per cycle. That's 10% at the 450KHz minimum operating frequency, which I'd think is enough time for a nearly-balanced core to reset, right?
Cheers, James Arthur
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