Snubber Circuit for Power Diode

Snubber Circuit for Power Diode

The snubber circuit is nothing but a protection circuit, to protect the power semiconductor devices.
When the power diodes are using in switching applications (like smps circuits), the snubber circuits are essential.
In this post let us see the snubber circuit protecting the power diode.

It is recommended to refresh about the switching characteristics of Power diodes before proceeding further for better understanding.

We know that when the power diode turned off, the reverse recovery process will start. During this time, over voltage spikes will appear across the device, which should be eliminated. The snubber circuit is used for this purpose.
The snubber circuit for the power diodes consists of a resistor and a capacitor connected in parallel with the diode as shown in the following figure.

• When the reverse recovery current decreases, the capacitor will try to hold the voltage across it.
NOTE:

It is property of the capacitor to oppose the sudden change in voltage appearing across it.
It is property of the Inductor to oppose the sudden change in current flows through it.
• The resistor (R) is used to dissipate some of the energy (I2R loss) stored in the capacitor.

How to Choose the value of RS and CS?

From the datasheet of Power diode, we can get the the value of dv/dt and IRR.

The equation for the dv/dt across the diode:
dv/dt = (0.632 x VS) / (RS x CS)
Here Vs in not the supply voltage of entire circuit. It is the voltage applied across the diode.

The RS value can be calculated using the following formula.
Rs = VS/IRR

By knowing dv/dt and the RS , we can select the value of the snubber capacitor CS.