# Can someone explain this high-speed P-channel MOSFET drive circuitry?

I found this circuit in an application note on P-Channel Power MOSFETS.

The note explains that modern technology has made it possible for P-Channel MOSFETS to approach N-Channel performance in power applications. I would like to make a DC motor driver that uses high-side P-Channels, but there is very little info out there on driving them at high speeds. This circuit looks promising, but I do not understand all of it.

Here is what I DO understand:

• The two resistor pairs (Rh1/Rh2 and RL1/RL2) are use to set the amount of time each respective FET spends in the linear region (the time to charge up the gate capacitance). The diodes Dh/DL make it possible for the Rx2 resistors to set the rise time and Rx1 + Rx2 to set the fall time. The diode is orientated this way because it is almost always desirable to have a longer fall time than rise time.

• The zener diode Dz somehow clamps the gate-to-source voltage within an acceptable range, regardless of the supply voltage.

Questions I have:

• How does the capacitor Ch and the resistor Rz switch the FET on and off, and will this work for a range of supply voltages?

• How does the zener Dz clamp the voltage in the acceptable range for gate drive?

• Can this circuit keep the MOSFET enhanced or depleted indefinitely, or does it require a pulse every-so-often to deal with Ch?

• What would the gate drive IC look like? Is this application referring to a micro-controller or something more current-capable? If a specialized driver IC is required, what are some example parts that could work, and what voltage range must they provide to Ch on the high side?

• The App Note explains perfectly well. Yes U need a continuous pulse where Rz Ch=T is shown by Fig 4. negative slope while +slope Zener is open so it is fast. Thus both turn off faster than ON. So there is dead time. Read the App note more carefully Dec 12, 2019 at 7:24
• To be frank, such simplistic passive drive circuits are always an approximation. If you want tight control over switching losses, you'll want a closed-loop gate controller that slews the channel current in a controlled fashion. Apr 2, 2022 at 4:22