Hello,

Hope this is the correct category to ask:
I made a circuit based on an NE555 to control the speed of a blower motor via PWM.
The output of the 555 triggers a MOSFET butthis one gets really hot with increasing frequency.
So out of interest I tried controlling it analogue via a resistor to the gate/base- and it also gets hot.
I tried different componants, they all get hot, despite the motor being below the rated amps of the MOSFET (or transistor).
Componants I tried were: IRFZ540N (33A), IRFZ44N, C5905 (20A).
The motor is rated for 12V (tested with 14,1V), uses 5,3A continuously at 14V, 0,06 mH inductance, 0,8 Ohm resistance. It's from one of those Chinese (Webasto copy) diesel heaters.
Have attached a circuit image.
Can anyone point me into a direction of where the reason for this can be found?

 

Welcome to AAC!
What is the value of R2?
What diode types (no designators provided) are you using?
What size/type of heatsink are you using for the FET?
Note that the 33A rating of the IRFZ540N is only if you can keep its case temperature down at 25C. Also, it needs a Vgs of 10V to turn on fully; which leaves only 2V across the motor because you are driving the blower motor high-side. With a Vgs less than 10V the FET will be only partly on, so its drain resistance will be higher and it will heat up more.
Try driving the motor low-side.

 

Can anyone point me into a direction of where the reason for this can be found?

As Alec_t pointed out use Low side switching if using a N channel mosfet.
If not possible using Low side then a P channel is required.

 

Hello,

R1 seems to be quite low.
What is the value of R2?
The timing capacitor is quite large with 220 uF.
The capacitor on the cv input of the 555 is incorrect, usualy a capacitor of 100 nF is used there.

What is the stall current of the used motor?

Have a look at this page for the values in the 555 circuit:
https://theorycircuit.com/ic-555-ic-741/adjustable-duty-cycle-pwm-generator-circuit/

Bertus