Got a project that involves a certain amount of power conversion...
A flyback converter seems a plausible approach. There's a handy transformer that's decently compact and will handle plenty of power if I run it at, oh, 500 KHz or so.
Heat will be an issue, eventually, so I pick a reasonably cheap, reasonably small, SMT FET with ~ 4 mΩ ON resistance.
Then, look for a chip to control it. Needs to handle flyback, of course, and 500+ KHz, and sufficient supply voltage.
Such beasts tend to be of the current-mode persuasion.
And, for reasonable peak current, they want about a 25 mΩ resistor in series with the FET's source.
Which rather defeats the purpose of the low ON resistance, dunnit?
Yeah, there are current-sensing FETs... but I'm not finding one in a dinky package.
Oh, well. More searching for suitable chips, I suppose.
Though: 2 A through 25 mΩ would be 100 mW, which is not a terrible loss. Of course, the actual loss would be a few times that, peak, and the average would depend on the duty cycle and details of the waveform.
And: I suppose I could do fixed-frequency regulation with an MCU. Which seems a totally dumb idea, until factoring in my desire to have the output voltage selectable among various options, and then suddenly it almost seems to make sense. And I have done flyback PWM control, with an AVR, for a really itty-bitty transformer. Maybe time to revisit the transformer's specs, and the PWM options available in small AVRs.
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