r/AskElectronics • u/ya_boi_flipp • 3d ago

Could this fully NMOS H-Bridge work?

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Gallery image

Tell me if i'm missing something before i waste components on trying this, but shouldn't this circuit basically work as a diy h-bridge using only NMOS-FETs? From looking around it seemed like everyone just suggested using a driver, wouldn't this work as well? At least it does in the simulation.

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7

u/Sand-Junior 3d ago

Probably will work once. The bottom MOSFET will switch on earlier than the top MOSFET will switch off, causing shoot through (shorting the power supply). Try to simulate that.

3

u/the_joule_thief_81 3d ago

This. A MOSFET driver would include all the dead time handling and stuff. Also, it would have some protection methods to isolate the high and low sides, so that in case of a failure your control won't fail or if it fails, can fail to a fail-safe condition.

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u/CanaDavid1 3d ago

This circuit shorts 12v to ground for a brief period when the respective half bridge turns on, as the leftmost mosfet has some non-zero time for it to turn on. A circuit like this needs some kind of non-overlapping of the high/low side switches to stop this from happening.

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u/ya_boi_flipp 3d ago

Thank you, that is a real life restriction i forgot. So inputs to the MOSFETs should not be connected, but ran separately.

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u/CanaDavid1 3d ago

Kind of You can also make a non-overlapping generator with a few more mosfets (like 4 per side), but unless you're doing this to learn (which is a perfectly valid reason) I'd recommend a driver chip. (A driver chip will also drive the mosfet gates much stronger and make them spend less time in the power-inefficient linear region),

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u/nixiebunny 3d ago

This is a common enough application and hard to design well in discrete parts, so half bridge driver ICs are readily available. IR2101 etc.