PWM Mosfet driver keep dieing

Thread Starter

lostsoul

Joined Oct 13, 2015
2
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 ? ???
 

Attachments

KeithWalker

Joined Jul 10, 2017
1,031
You need to introduce a delay between switching one FET off and the other FET on, otherwise, delays in the switching will cause both FETs to be on at the same time which shorts the supply through them.
Keith
 

shortbus

Joined Sep 30, 2009
7,760
What is your input voltage, shown as Vs, to the IR4427? Is your mosfet heat sinked? And isolated from the heat sink? Why use 2 mosfets? They, in the data sheet, just showing it CAN BE used for 2 not that it has to be used that way. Why no pull down resistor on the gate?
 

ElectricSpidey

Joined Dec 2, 2017
1,175
Your circuit should have some load sharing resistors.

But the obvious is...Chinese MOSFETS?

Your post is a little confusing, is it the drivers that are blowing or the MOSFETS?
 
Last edited:

KeithWalker

Joined Jul 10, 2017
1,031
20 KHz is a high frequency for PWM motor control and is usually only used with coreless motors. That may be causing your problem. Try dropping the frequency to a more usual frequency of 2 to 3 KHz and see if that helps.
Regards,
Keith
 

shortbus

Joined Sep 30, 2009
7,760
20 KHz is a high frequency for PWM motor control and is usually only used with coreless motors.
It hasn't been that long ago that 20KHz was the recommended frequency for all DC motor PWM controls. I know they dropped it down to ~18KHz but many of the old circuits are still out there.
 

KeithWalker

Joined Jul 10, 2017
1,031
Actually, motor controls rely on the motor inductance having an effect. They use 18KHz and up to keep it out of the audible range. The higher frequencies cause more trouble because the switching delays in the MOSFETs cause them dissipate more power.
Keith
 

Alec_t

Joined Sep 17, 2013
11,398
Do you have a star ground system? Without that, heavy motor currents could cause 'ground bounce' which could affect the driver IC operation.
 

MrAl

Joined Jun 17, 2014
7,663
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 ? ???
Hello,

One of the possibilities is higher voltage spikes appearing at the drains. Keep the wiring as short as possible going to the motor diodes, check with a good scope, then add a snubber if needed. Note the back emf diodes dont do enough if the wiring is too long and then you need a snubber. The snubber wireing should be very short connected directly across the mosfet source and drain, one snubber per mosfet for a total of two snubbers.

Another is wiring between gate driver, gate, and mosfet source terminals. The driver wiring to the gate and source should be absolutely very short. The common of the gate driver should have a separate wire that goes to the source(s).

Of course you need to check the current ratings of the mosfets and make sure they are sharing the load as expected. Load sharing of mosfets is not straightforward as we might like the difference in switching speed also plays a part in the power dissipation so you may have to measure the switching times of each mosfet.

Sometimes you can solve problems like this with proper measurements, other times you just have to keep trying what is known to work on other long standing circuits. That means observing all of the above and implementing anything that might help until at last the problem is solved.
Let me be the first to welcome you to the illustrious discipline of hands on engineering.
 
Top