Mach 3 PWM output to direct drive a MOSFET

[dex918]

Hi,

Can someone confirm if the Mach3 PWM ouput from the parallel port can be used to drive the Mosfet to control the spindle speed?

My idea is like below.. Need to add a speed sensor for feedback to the Mach 3.

[H.O]

Look at the Vgs parameter for your MOSFET - most of them wants 10-15V on the gate to saturate but there are "logic level" ones available that seems satisfied with 5V. A flyback diode across the motor is probably a good idea and a proper MOSFET drive between the LPT-port and MOSFET too but then the partcount starts to go up...

Another thing to consider is that the frequency output from Mach3 is rather low as its original intent was to low-pass filter it and get an analog signal. It is possible to specify the frequency but the higher you go the lower resolution you get. If you're running at 45kHz and specify a frequency of 4500Hz you'd only get 10 discrete speeds - or duty cycles rather.

/Henrik.

[dex918]

Hi Henrik,

I appreciate the reply. Looking at it, looks like I have to abandon the idea unless I can:

1. Add a freq multiplier
2. Use a Logic level MOSFET (expensive!)

Regards.

Dexter