MOSFET control using PWM & 16C711?

[penelopepug]

You can control a mosfet or hextfet directly with a HWPWM or PWM output from a PIC but there are some things that you need to do to limit heat disipation; 1) Select a hexfet (of mosfet) with the lowest RDSon you can find or afford. 2) Select one which is logic level controlled. 3) Select one with minimal gate capacitance. 4) Limit the frquency of the PWM signal to as low as you can in your PWM or HWPWM command string. The PWM signal will produce fewer pulses per cycle at a lower frequency. The fewer pulses per cycle results in less rising and falling edges which accounts for much of the heat a hexfet will generate. These are linear states where the hexfet will be highly resistive. 5) You can use a hexfet gate driver to drive the gate hard and fast AND, you can drive it at a higher voltage too with a driiver IC.

I have built many PIC based PWM circuits that serve as motor speed controllers and light dimmers that run cool using these techniques.

Another note (or two); PIC based PWM has always posed a problem for me because it is generated in spurts. So your loop timing will make the spurts (or burts if that is a better term) of PWM more or less noticable. HWPWM is continuous and much better. Lastly, I am not sure why you would want to condition the sigal using an RC network. This will result in a linear state and cause the hexfet to be resistive and thus, dissipate lots of heat.