I am trying to design a circuit to control the speed of a motor using PWM.
I intend to run the PWM at (at least) 10kHz. The PWM library I am using allows 1024 steps for the duty cycle (0 to 100% in 1024 steps.) The smallest "on" time is about 98 nanoseconds.
I assume that I need a MOSFET with a switching time faster than that.
From what I see in the datasheets, I need to find a MOSFET with a total time of less than 98 nanoseconds for the following parameters:
- Turn-on delay time
- Rise time
- Turn-off delay time
- Fall time
Taking the IPA60R360P7S as an example, I find the following values:
|Turn-on delay time||8ns|
|Turn-off delay time||42ns|
That gives a total of 67 nanoseconds.
- Would this MOSFET be fast enough for the shortest PWM pulses?
- What makes it fast enough - that is, how can I tell?
- How close can the pulse width and the total of the time parameters be before the shortest pulses are distorted?
- What other parameters of the transistor should I take into account to find the shortest pulse time?
Switching the gate fast enough is a separate problem. I'll be using a gate driver for that, but I haven't picked one out yet. I want to understand how to pick the transistor first.
Yes, I do need that 600V rating on the MOSFET. I'm going to be driving a small (100 watt) universal motor on rectified AC mains (240VAC.) I think less than 600V would be too close to the 340VDC of the rectified mains.
The final PWM frequency will be as high as the microcontroller will run without skipping pulses. I don't want to hear "squeeeeeee" while the motor is running, and I don't want to hear "mmmmmmm" either (from low frequencies.) This will be on a sewing machine, with the motor about a foot from my head when I'm working. The machine itself is the next best thing to silent - I want to keep it that way.