Re: [CAD_CAM_EDM_DRO] Why Bipolar?

----- Original Message -----
From: Jon Elson <jmelson@...>
. Driving the
> high side FETs is easy compared to driving high side bipolar transistors,
> since no gate current is needed.
>
> Jon

Hi Jon,
Power MOSFETS certinly do require gate current! those gates are around 1500
to 2500 picofarads and you have to charge and discharge that capacitance to
turn them on and off. There is also miller capacitance between the gate and
drain so if you are switching high voltages the inverted signal at the drain
will fight the gate current. For high frequency switching as in a power
supply or chopper drive your gate drive circuit needs to be able to drive
about an amp (for a very short time) to get good switching speeds from the
FETs. I usually use a bipolar totem pole transistor driver 2n3904/2n3906
with a series resistor to limit the gate current to one amp.

Joel