How to design a snubber circuit?

In this article, you will learn what is snubber circuit? Why we need to use snubber circuit with power electronics circuits across semiconductor switches ? What types of snubber circuits are used in power electronics circuits. Let’s start with basic definition of snubber circuit.

What is snubber circuit?

Snubber is basically a RC circuit which is used to minimize back emf voltage or dv/dt with in a limit of semiconductor diode. It is connected across semiconductor devices. It is very important part of power electronics circuits. It provide protection to semiconductor devices used in power electronics circuits. Power electronics devices protected from reverse voltage through snubber circuit.

Types of Snubber circuits :

 Three type of snubber circuits are used in power electronics circuits. Name of  three of them is given below:

1. Forward polarized.
2. Reverse polarized.
3. Unpolarized Snubber circuit.

Forward polarized snubber:

It is more appropriate for when a diode is connected anti parallel to transistor or thyristor. Circuit diagram of Forward polarized snubber is shown below:

Resistor R1 is used to limit dv/dt voltage across semiconductor device. Resistor R2 control the discharging current of capacitor C1 during the turn on time of semiconductor device.

Reverse polarized snubber :

Circuit diagram of reverse polarized snubber is shown below. Resistor R1 limit the reverse voltage dv/dt. R2 discharge the capacitor. Advantage of reverse polarized snubber circuit is that capacitor doesn’t discharge through semi conductor device. Due to which losses are reduced.

Unpolarized snubber :

Unpolarized snubber circuits are used when two semiconductor devices are connected anti parallel to each other. Just like shown in figure below. In this circuit snubber should work in both directions. That is why unpolarized snubber is used in such situation. Circuit diagram of unpolarized snubber circuit is shown below:

To design a snubber circuit you should know about following things of snubber circuit:

• reverse recovery time of semi conductor device
• Current rating of semi conductor device
• Circuit total inductance
• Input voltage to circuit
• Optimum value of current factor (It can be found from data sheet of semi conductor device)
• Optimum damping factor

If you know above things you can calcualte vales of capacitor and  resistors using following formula’s :

 C = L [ Ir / dVs ]²

R = 2δ√LC