Driving a high side switch/mosfet/etc. from a 3.3V PWM output at 20kHz?

Thread Starter

wittrockvita

Joined Nov 13, 2020
2
I need to drive a high side switch (mosfet or equal) from a 3.3 output at 20kHz. The load requires 15V - 3 Amp.
Haven't been able to find any suitable solition, så if any of you can push me in a good direction It will be highly appreciated!
 

Thread Starter

wittrockvita

Joined Nov 13, 2020
2
How about a P FET with the gate pulled up to source with a resistor. Then either a N FET or NPN to pull the gate low when needed.
That is not posible at 20 kHz PWM because of the large gate capacitance of a mosfet - the resistor can't simple chrge it fast enought even if it very small.
 

dl324

Joined Mar 30, 2015
13,519
That is not posible at 20 kHz PWM because of the large gate capacitance of a mosfet - the resistor can't simple chrge it fast enought even if it very small.
It's likely worse than that. A pull up resistor to 15V would be forcing current into the output of your uC. If you exceed the maximum voltage allowed or current forced in to the output, you'll trigger the parasitic SCRs that exist in all CMOS devices.

To do it "right", you need a level shifter, inverter (or two), or a gate driver.
 

ronsimpson

Joined Oct 7, 2019
1,650
V1 is the signal from the computer 0/3.3V.
V2 is the 15V supply.
M1 is a P-MOSFET (not logic level)
R3 amplified by Q2 turns off the MOSFET. I used Q2 to speed up turn off time.
Q1 turns of the MOSFET.
When V1=3.3V, q1=on, M1=on.
1605380350805.png
 
That is not posible at 20 kHz PWM because of the large gate capacitance of a mosfet - the resistor can't simple chrge it fast enought even if it very small.
Your response to my poor suggestion may have answered a failure in a current project of mine. I've never had to consider speed before in my own projects. Good luck.
 
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