I've seen N channel MOSFETs as high side switches of H bridges quite often, which requires a charge pump to drive. Wouldn't a P channel MOSFET be easier, simply isolating the microcontroller command from the gate source voltage? Why use the N channels instead then?

  • 2
    \$\begingroup\$ Well, then you need the charge pump to turn it off instead of on, not much difference \$\endgroup\$ – PlasmaHH Apr 14 '15 at 10:34
  • \$\begingroup\$ @PlasmaHH, there's quite a difference. You need only a transistor to control a P-channel MOSFET. \$\endgroup\$ – avakar Apr 14 '15 at 11:12
  • \$\begingroup\$ And the difference is, fundamentally, that using P-channel on the high side, the control voltages are all bounded by the motor supply rails. The charge pump (or some other aux supply) is needed to generate a control voltage above the supply. \$\endgroup\$ – user_1818839 Apr 14 '15 at 11:38
  • \$\begingroup\$ @avakar if decent efficiency is to be realized on medium to high power H bridges, a single transistor is not enough to control a P channel MOSFET - it would need a push-pull driver and this will need some form of charge pump on medium to high voltage supplies. \$\endgroup\$ – Andy aka Apr 14 '15 at 11:51

P-channel MOSFETs tend to have a higher Rds(on), making them less efficient (for the same price). For a small H-bridge, the simplicity of using them makes them practical

However, for high power applications, the extra complexity of driving N channel FETs can be justified by improved efficiency from lower Rds(on).


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