How calculate maximum PWM frequency for MOSFET
How calculate maximum PWM frequency for MOSFET
(OP)
Hello all,
I would like to know what the maximum PWM frequency would be that I can drive this MOSFET:
http://www.vishay.com/docs/72439/sum110p06-07l.pdf
There are a lot of delay times given but even if I take the highest number (200ns) for 'turn-off time' this would result in 5 MHz. But this would mean that even on a 95% duty cycle the MOSFET would still need it's 200ns to go off... So the Hz number has to be much lower.
Here its seems that I would need some insight on how to calculate this. Let's say my PWM resolution is 256 just as a calculation example.
Thanks
Markus
I would like to know what the maximum PWM frequency would be that I can drive this MOSFET:
http://www.vishay.com/docs/72439/sum110p06-07l.pdf
There are a lot of delay times given but even if I take the highest number (200ns) for 'turn-off time' this would result in 5 MHz. But this would mean that even on a 95% duty cycle the MOSFET would still need it's 200ns to go off... So the Hz number has to be much lower.
Here its seems that I would need some insight on how to calculate this. Let's say my PWM resolution is 256 just as a calculation example.
Thanks
Markus





RE: How calculate maximum PWM frequency for MOSFET
f = 1/T = 1/130ns = 7.7MHz to go on/off as fast as possible.
Of course that's pretty useless since just about no energy would be transferred. You probably want your PWM period to be 10 to a 100 times larger than 130ns so the ON/OFF delays remain insignificant.
Call it 1us.
Your maximum ON period would be 255us and your shortest period would be 1us.
We don't know what you're using this for so even those periods might be idiotic.
Keith Cress
kcress - http://www.flaminsystems.com
RE: How calculate maximum PWM frequency for MOSFET
RE: How calculate maximum PWM frequency for MOSFET
RE: How calculate maximum PWM frequency for MOSFET
There was made converters up to 70MHz, but efficiency is not so good to became an commercial product.
For a MOSFET in a power converter, maxim frequency is not a simple 1/(ton+toff); need to take care for gate charge remove time, that is a complex mechanism, very dependent of driver current and slew rate capability.
Also, to fast slew rate mean high di/dt that have implications in EMI and develop high voltahes on parastic inductance.
RE: How calculate maximum PWM frequency for MOSFET
Faster slew = more efficient.
Faster slew = more EMI
You need to find the sweet spot.
Use a good 'gate driver'.
Having only 3.3V will certainly cramp your gate driver selection. Probably down to one poorly data-sheeted Microchip part.
If you're doing high-side switching that often requires isolation. N-MOSFETs switch faster. And can used high-side once you're using a driver and maybe isolation.
Keith Cress
kcress - http://www.flaminsystems.com