[SOLVED] how to protect mosfet from inrush current

[alipoor90]

hi guys
i have a heater and i want to dim its heat with pwm
but in start time heater is cold and its resistant is low and mosfet probably damage due to inrush current
the time of inrush current approximately is 300ms
what can i do to protect the mosfet?
sorry for my weak English
best regards

 

[tpetar]

Your MosFET must have appropriate current and voltage capabilities for that device. Check datasheet.

 

[alipoor90]

can i use a series inductor to limit di/dt?

 

[tpetar]

I dont know what happen, just before few sec I saw duplicated posts, I delete latest duplicated, after that both post are deleted.

 

[rajudp]

are you using microcontroller or some pwm driver like 3525 to drive mosfet?

 

[alipoor90]

i use optocoupler and transistor to drive mosfet and the input of optocoupler is uC pwm output
tnx

 

[tpetar]

You can consider usage of soft start.

Inductor in serie also can be used but can have influence on normal circuit current.

 

[Hz2020]

u can also use NTC resistors that has a high resistance in the starting condition

 

[mtwieg]

The simplest method would be to simply have a soft start which ramps the PWM duty cycle slowly in order to limit the RMS current through the FET until the element starts to heat. That should work, assuming the FET can withstand narrow pulses of high current. Using a NTC ICL is also an option, though it will waste some power. A series inductor probably isn't feasible, since the thermal time constant of your element is probably very long (seconds), it would take a huge inductance to match that.

 

[andre_luis]

Don´t forget to consider that MOSFET PWM duty-cicle is operating under safe operating area ( SOA ):
That information is avaliable at device datasheet.

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