Mosfet driver bootstrap capacitor discharge on no-load?

[grizedale]

Hello,


Will the bootstrap capacitor on this high and low side driver stay charged up when the full-bridge smps goes on no-load?


NCP5181
https://www.onsemi.com/pub_link/Collateral/NCP5181-D.PDF

The SMPS is:-
Full-Bridge at 84KHz,
Vin = 210VDC -373VDC
Vout = +-40V
Pout = 335W

How much dummy loading will i have to add in order to keep the bootstrap cpacitor charged up?

 

[FvM]

The required condition is, that the low side switch has non zero on-time. Then the bootstrap cicruit will work, independant of the load.

 

[grizedale]

ok thanks, but no load means zero on time, so surely it cant be independent of the load.

 

[FvM]

no load means zero on time

I don't think so. Zero on time means no output voltage. But the feedback loop still maintains the output voltage at zero load. I don't know, if the circuit operates stable at zero load, but this shouldn't be a real problem, even temporary drop of bootstrap voltage and deactiviation of the high side driver won't be necessarily. I think, it's more a question to be decided by empirical tests than prediction.