AC fan pwm control using MOSFET


Joined Sep 20, 2005
Since im controling ac i will b needing a separate dc supply for driver, ryt? so wil these two supplies hv isolation btw each other? coz that same dc supply will be provided for d pic generating pwm. so any pbm at d output side of d driver must not effect other circuits. dats y im little afraid of using such a driver. i came through drivers dat need VCC lyk dis. but didnt chose due to this. so im not clear abt dis VCC supply provided to driver. will dat b isolated frm d line...???
First, could you try speaking English and using paragraphs? This is very hard to read..

Basically, you need two supplies. One is a typical transformer supply to power the PIC.
Second one can be anything, for example a simple zener, but that will waste a lot of power so it will be hard to keep it cool.
Better solution is to get a transformer that has two separate windings. One winding will power the pic, the other winding will power the driver and will be at line potential. You just need to keep the traces/wires of the secondaries far enough from each other to make sure the line voltage can never get into the pic circuit. The optocoupler will provide isolation between the pwm signal and the mosfet, you just need to be precise with the connections to keep everything safe.
Also connect the protection earth (PE, green-yellow cable) to the ground of your PIC circuit, just to be sure that if something bad happens it blows the fuse or trips the GFI instead of electrocuting you.

Thread Starter


Joined Nov 17, 2011
Sorry for the inconvenience with my language.

I got your idea. I already have an isolated supply for the pic producing pwm. What if i use a pulse transformer instead of driver to control the MOSFET, at its secondary? Then i could use an opto to provide current to the primaryside which switches according to the pwm from pic. Is there any problem if i use pulse transformer for high frequency (>20Khz) switching?