MOSFET gate current / waveform. Does it vary with load on the device?

[Chris Wilson]

Does a MOSFET's Gate current vary with the load on the device across Drain and Source? If you `scope a Gate switching waveform, say in a SMPS, does the load affect the waveform? Thanks. Just curious as the driver IC for the Gates is advertised as being able to deliver up to 1.6 Amps, and I don't see why such high currents would occur. As an example here's my waveforms on two paralleled pairs of IRFP450 devices. There was no voltage / load on the output at the time. 136 kHz drive frequency. Will this vary when they are loaded?

[retrolefty]

MOSFET gate current flow is only during the charging and discharging of the gate capacitance during transition between on and off or off and on, at DC conditions there is no gate current drawn even at full rated drain current.

[c4757p]

During switching, yes, absolutely the load affects the gate current. MOSFETs suffer from the Miller effect like nothing you've ever seen before...

[T3sl4co1l]

FWIW, 1.6A is pretty weak as a driver, but that's okay as 136kHz isn't terribly fast, and IRFP450 is a pretty terrible device, very old.

Tim

[Chris Wilson]

OK, thanks, I'll read up on the Miller Effect later. As a matter of interest is there a more modern device that would replace the IRFP450's without a total circuit re-design? Cheers!