Author Topic: PWM mosfet driver die  (Read 844 times)

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Offline lostsoulTopic starter

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PWM mosfet driver die
« on: May 11, 2020, 10:13:37 pm »
Hi everyone,

since some time i am fighting with this driver, i need to control a blower (hvac), it is brushed motor, inrush current bit lower than 18 amps, pwm from PIC running at 20 kHz.  I've try with some chineses H Bridge (using only half), single mosfet, parallel mosfet, always fries after few minutes. I have a basic osciloscope ( hantek measure DC only?)

in the pictures, yellow line is source PWM (after driver IR4427) and green on the motor (measure mosfet drain, inverted probe), this driver was the last, with H bridge there were clean flat signal on motor.
PIC uses soft start (low duty cycle and increase slowly until desired duty)

what am i failing ?  ???

Thanks
 

Offline Picuino

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Re: PWM mosfet driver die
« Reply #1 on: May 11, 2020, 11:19:27 pm »
How is the wiring?
Cables should be short and avoid large loops
 

Offline WattsThat

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Re: PWM mosfet driver die
« Reply #2 on: May 12, 2020, 01:38:12 am »
The yellow trace is the gate drive? It appears to be 5 volts peak to peak if I’m reading the display correctly.  If so, that’s probably the issue as the IRF3205 requires 10 volts on the gate to fully form the channel.
 

Offline lostsoulTopic starter

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Re: PWM mosfet driver die
« Reply #3 on: May 12, 2020, 09:37:46 am »
How is the wiring?
Cables should be short and avoid large loops

Cable to circuit has around 1m, and driver to the motor around 30cm


How is the wiring?
Cables should be short and avoid large loops

Yellow is signal coming from PIC to both inputs os gate driver (IR4427), green probe connected to low side of motor
 

Offline Picuino

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Re: PWM mosfet driver die
« Reply #4 on: May 12, 2020, 01:13:21 pm »
The green line shows two strange behaviors.
The top of the signal shows an oscillation of about 50kHz and should be flat. So I said there must be stray inductances in the cables (they are a bit long)

At the bottom you can see a small step as if the mosfet did not switch completely well until the end of the cycle.

One reason I can think of for those mosfets to burn out is that the switching can be very fast and a short circuit occurs while the recovery time of the diodes. But those diodes are quite fast and the Mosfets very robust.

Another reason may be spurious switching voltages caused by stray inductances in the cables. The cable from the mosfets to the diodes should be as short as possible (few millimeters). Or else add a Snubber network to the mosfet.
« Last Edit: May 12, 2020, 01:15:33 pm by Picuino »
 


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