Calculating the Resistance and Capacitor for a Snubber Circuit with 3HP DC Motor

[bencyp]

Hi,

I have build a PWM to control a 3HP DC motor. The problem is that the MOSFET is getting damaged because of high return current/voltage. I used a Diode at the motor end but that diode is also getting burnt.

Main DC 380 Volt
PWM used to control a 220 DC 3HP motor

I found out that a snubber circuit is need to take up the spike generated by the motor when the MOSFET is switched off. Can anyone help me with the exact calculation of Capacitor and Resistance needed for Snubber?

Regards,
Bency

 

[berkeman]

Generally with the snubber circuit, you will size the capacitor to resonate with the power inductance at some frequency, and will size the resistor to damp that resonance rather strongly. You want to use the cap to temporarily absorb the transient energy, and the resistor to dissipate it over about a half cycle of the LC resonance.

I googled snubber circuit tutorial, and got lots of good hits. Here's an app note from Maxim, for example:

http://www.maxim-ic.com/appnotes.cfm/appnote_number/848