Suggest me a snubber circuit for driving DC motor PWM

[T Quadir Choudhury]

Have a DC(pm type ) Motor 180V, Full Load Current ~ 3A (1 HP)
I was using a circuit with 555 generating square waves and PWM (modulated) to control speed. Was using IRF250N.
When driving a small motor was OK but when using as above the MOSFET was destroyed.
Can anybody suggest a snubber ckt for the above combination. No I dont know the inductance of the motor. May be some values with which i can begin experimenting

 

[xaccto]

Re: Driving DC motor PWM

did you have a reverse diode across the motor ?

 

[alexan_e]

Re: Driving DC motor PWM

You mosfet is also quite close to your supply voltage with a max Vds of 200v, use a higher voltage mosfet.

Alex

 

[T Quadir Choudhury]

Re: Driving DC motor PWM

yes, the diode got hot and burnt. I also forgot to mention that the 555 was producing Sq wave at 1.5k Hz, only PW was modulated. There was the question of what fast diode to usel

---------- Post added at 06:20 ---------- Previous post was at 06:18 ----------

Thanks, I will see what is available here

 

[alexan_e]

One more question because it is not clear from your description, do you have a proper mosfet driver or do you feed the 555 output directly to the gate?
If you don't have a proper driver then the switching losses on the mosfet will be high (slow turn on/off) and this will increase the power consumption and heat on the mosfet.
In small loads you may get away with it but as the load voltage/current increases you will have problems.
Does your mosfet overheat?

Alex