what is the relation that I have to take into account when I select a mosfet(or a transistor in general) for pwm driving about rise/fall/turn off delay/turn on delay and the PWM frequency? How to compute the maximum frequency?
Thanks
Edit: Thanks to all, but I was searching, if it exists, a formula that can put in relation the situation in which my PMOS can completely charge/discharge without having additional heat, using the time mosfet parameters, and the maximum PWM frequency
Best Answer
You can rearrange \$i(t) = C \frac{dV}{dt}\$ to \$\Delta t = \frac{C\Delta V}{I}\$ where \$C\$ is gate capacitance, \$\Delta V\$ is your change in gate voltage, \$I\$ is the current the driver is capable of sourcing/sinking, and \$\Delta t\$ is rise/fall time. That will get your close. You want to find the MOSFET with the lowest gate capacitance you can find, while meeting any other specs.
When your rise/fall times start getting to more than a few percent of your PWM period, you need to start thinking about putting in a dedicated gate driver IC, or at least make one with of a pair of bipolar transistors, kept out of saturation.