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Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
I understand that with a regular buck converter, it requires high side gate driving techniques...
Would it still be needed with a P-channel mosfet in it's place? And how would you go about driving it anyway, since it needs to be all negative and whatnot.
Like this, could I just use that with a SG3525, or something similar to make a buck converter? (no high side chip needed, apparently!)
Registered Member #1792
Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527
wrote ... I understand that with a regular buck converter, it requires high side gate driving techniques...
Would it still be needed with a P-channel mosfet in it's place? And how would you go about driving it anyway, since it needs to be all negative and whatnot.
With a p-channel you can use low-side driving, though the voltages involved can still be quite large if you have a high input voltage, so make sure to check the Vgs,max rating. You don't need negative voltages, just negative polarity: A positive gate voltage equal to the input voltage (applied to the source pin of the FET) will turn it off. A zero gate voltage will turn the FET on. You need to check the Vgs,max rating for the on-state, because if you have a 25V input on the source, 0V on the gate, you have Vgs=-25V which is pretty big.
Some switching regulator control chips are nice enough to provide you a gate waveform of both polarities, but the most common output will be for driving the N-channel MOSFET. You can convert it for use with P-Channel MOSFETs by running it through an inverter.
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P-channel mosfet Buck Converter...
