MCU Reset with DC Motor driving (PWM)

Question

I would like to understand a problem which i have with a little MOSFET test with a dc motor. My power supply drive the motor at 12V and it consume 1A.

My circuit is very basic. I have a stm32 MCU which drive a mosfet (IRLR2905ZPBF).

My motor is connected between the dc motor output and the ground. I don't need a H-Bridge.

When i increase my PWM ratio softly from 0 to 100% my dc motor works prefectly but when my motor is stopped and i put a 100% value on my pwm command, there is a big surge (i think to start the motor from stop state). So my 12V power supply is falling and i obtain a MCU reset.

I had a 100uF bulk capacitor but no better results.

Thank you very Much.

Adrien

Answer 1

Do you happen to have an oscilloscope that you can use to look at the power supply? If you do, look to see if you are seeing an initial dip in the power supply. You may be having a very brief dip in the power supply due to the surge current. That dip could have a fall time of a few nanoseconds. If that is what you are running into, then a 100 uF bulk capacitor has so much lead inductance and it will act as though it is not even there. In that case, you need to add something like a 0.1 uF ceramic capacitor with very short leads instead. The bulk capacitor supplies the long duration burst of current and the small decoupling capacitor(s) take care of the spikes.

Answer 2

From your schematic, it does not look like the motor is connected properly.

Stopping a motor quickly will generate a large negative voltage spike called back EMF. To mitigate this, you can install diodes in reverse bias across the motor. This provides a resistive route for the energy which dissipates it quickly. You can install a second diode in series to increase the rate.

^{simulate this circuit – Schematic created using CircuitLab}