I'm using an IRFZ44N power MOSFET to drive a DC motor (24v, 4kgcm, 2A, FLRPM 500.) I found from the datasheet that the IRFZ44N has an ampere rating of 49A and still it is getting very hot.
Here is the schematic:
The IRFZ44N is driven from a PWM of 244 Hz. I found that it only gets hot at low duty cyclex. At higher duty cycles the MOSFET is not heated at all.
What might be the possible reasons?
Best Answer
While I was writing this answer, @Connor posted an answer covering most of it. In any case...
There are a few things that need to be addressed in the presented circuit.
R3 = 4.7k ==> Ig < 5.1 mA
. This current charges up the substantial gate capacitance at each rising edge for Vgs to rise, and is way too low. This will cause Rds to rise very slowly, and while in this rising part of the graph, the MOSFET will waste a lot of power as heat.If the rather high PWM frequency mentioned is not really needed, consider moving to a far lower PWM frequency: 500+ Hertz is often good enough, but 20-30 KHz is typical, so as to be beyond human hearing and therefore PWM noise from the motor. The higher the frequency, the greater the percentage of time the power MOSFET will be in its intermediate transition stage, rather than on or off. Therefore, more heat.Edit: 244 Hz as updated by OP is much more realistic.