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LM5106 as a DC power driver

Nick Wernicke
Intellectual 775 points
Other Parts Discussed in Thread: LM5106

I'm using the LM5106  to drive half bridge from some PWM all the way to DC. If you're curious about the application, this is for high voltage logic of secret pattern/type, and of course it needs feedback to verify what is being sent.

My concern is that at DC, the bootstrap capacitor and gate charge will leak down after a few seconds and will shut off. So I added a 100k resistor to trickle charge the bootstrap capacitor at ~90uA so it can stay charged at DC. I've never seen it done like this, so I am here to ask if anyone else has and maybe this is a bad idea.

In my schematic, there is a 9 isolated supply between Veh+ and Hi Drv.

Will this work to keep the high side gate 'on' for some arbitrarily long time, like 10 hours?

  • 0
    TI__Mastermind 25570 points
    Hi Nick

    I was initially skeptical but looking at it again, I think it would work. The trickle charge current will flow in the output resistors, R56 and R57. If there is no current in the 30V zener, then the potential divider ratio will be unaffected and the comparator will trip at the proper point. The key is to provide some path for the charging current to return to Veh-.

    The other way to do this is to build a little isolated 12V supply and use that to directly charge the bootstrap capacitor - but that's a bit more complex than what you are using there.

    Regards
    Colin