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Why the power mosfet in this circuit blow-up?

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powersys

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Could someone pls advise why this power mosfet (IRFZ44N) in the circuit shown in figure below blow-up? I tested TWO mosfets and both also blow-up.


mosfet_blow.gif


Spec of IRFZ44N
mosfet_blow_2.gif
 

IanP

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Add a (freewheel) diode accross the motor (cathode to +V) and this should fix your problem ..

Regards,
IanP
 

@t

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There is an overvoltage protection inside the FET, so it also can be the inrush current caused by the motorwindings in the start (not yet moving) position.
Measure the resistance (ohms) of the motor, than you can calculate the startup current. (V/R or 12/resistance in ohms) answer in Amps.
If the current is the reason then a serial resistor (0,x ohm) can solve the problem.
The mentioned fly-back suppressing diode should be used too I guess.
Succes, At.
 

vicky

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DEAR IANP SUGESSIONT SHOULD SOLVE YOUR PROBLEM
 

pisoiu

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Spikes may drive the gate over the Vgs abs. max.

/pisoiu
 

happy2005

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use freewheeling diode with inductive loads always. diode should be fast enough and its reverse recovery should be low.
Additionaly, don't connect the gate pin directly. Use series resistor(~10-1000 ohm) and a zener clamp to protect the Vgs voltage (should be less than +/- 20V).
Motor start-up current is very high but in this circuit mosfet is over rated according to dc motor. Still, the cable between battery and the power circuit should be as low as possible (or connect bulky capacitor at the power input of the circuit)
regards,
 

mostafa0020

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The circuit as shown has no switching driving ciruit to drive the mosfet gate, , as u connect the gate to the 12 v positive of the battery , means that the motor operates continously, i.e. no inductive overvoltage will happen,.

This makes the o.v. cause out of occurance, i think the mosfet explodes due to insufficient gate voltage to achieve linear c/c's which means that the mosfet has a certain high forward resistance , causes a lot of power loss, which in turn , cause the Mosfet to thermal overstress and run away.

Try to increase the voltage to be 15 V, or insure that the Rds"on" is very low and in the given range of datasheet. also , u can assure the adequate firing gate-source voltage by constructing load line on the Vds-Id curves for this mosfet given by its datasheet, and find the most suitable Q-point which is as near to the vertical current axis " linear region " as possible.

Regards..
 

powersys

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mostafa0020 said:
The circuit as shown has no switching driving ciruit to drive the mosfet gate, , as u connect the gate to the 12 v positive of the battery , means that the motor operates continously, i.e. no inductive overvoltage will happen
Agree with u... I think the mosfet is not driven as a SWITCH. But I thought the VGS(TH) is 5V only. So, 12V should far enough to drive the mosfet as a SWITCH. Pls advise.
 

IanP

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According to the IRFZ44 data sheet - see picture below - 12V UGs should be more than enough to operate this MOSFET as a switch ..

Regards,
IanP
 

mostafa0020

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Yes, it is very enough, i just thought this as a common failure mode for Mosfets and IGBTs.

I think a loose connection to the mosfet gate can cause bolw-up due to arbitraty firing " noisy ".
 

pico

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Try to put the gate protection diodes.
 

raybo

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nobody mention dv/dt or di/dt just put a snubber across the mother and it will work it helps if you got a scope otherwise try 100 ojhms a nd .22mfd in series
 

happy2005

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lots of advice for you: freewheeling diode, snubber, dv/dt and di/dt protection, gate protection, lowering on resistance etc. if your problem still exist, i think, you should check the dc motor.

Probably the dc motor doesn't rotate at startup occasionally. If it occurs, even first time, the battery is short circuited by the MOSFET because of motor internal resistance is very low. i did see this situation before. motor doesn't begin to rotate at startup and need very very high startup currents. So, the mosfet blows up because of high currents.
I think only solution to this problem is using another dc motor which doesnt cause this problem. Or you can put a suitable series resistance to the motor to limit surge currents to protect mosfet.
 

powersys

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Have measured the resistance of the dc motor and it's around 1.9 ohm. So, the starting current should be around 12/1.9 = 6 A, which is still far below the rating of the mosfet. Any other comment? Thanks.
 

riku

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hi.............
its because of high current at the start of operation which the MOSFET can not withstand:?:
 

v_c

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How is the motor turned on?

The circuit that you show corresponds to the system in its normal working mode but how is the power applied?

Is the power coming from a switched 12V system when it is active after your turn the ignition switch or is the 12V always available regardless of the ignition switch.

Best regards,
v_c
 

PaulHolland

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Hi. Put a diode (fast type) accross the MOTOR K should be connected to the +12 V. The gate should be connected through a resistor (10K) with the +12V. On the gate place a zener diode of 15 V to ground and all your problems are gone. If you want to limit the startup currents place an capacitor parallel to your zener diode. (10uF).

regards,

Paul.
 

riku

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ya........ wat my friend PAULHOLLAND told is right .......... we will use capacitor to control the current flow.......... but the fact is that at t=0, capacitor work like a short circuit ........... After this the circuit will work or not?
 

El-Hadidy

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Hello,

I suppose that the motor resistance and inductance are very low and so at the beginning of operation the motor back emf is nearly zero and the MOSFET acts as a short circuit across the supply.

Thank you

El-Hadidy

Added after 2 minutes:

Another comment is

This would occur if the motor inertia is very high at the beginning.

Thanks
 

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