# How to design a snubber for a flyback converter

## Jurassic World: Dominion Dominates Fandom Wikis - The Loop

01:25

A snubber circuit is essential for Flyback converter, to prevent the transistor from burning up. The overshoot on the transistor voltage, is due to the leakage inductance, , of the transformer.

## Variables

• - max power dissipated by the snubber resistor
• - snubber resistor
• - snubber capacitor
• - switching period
• - switching frequency
• - Input voltage to the converter
• - transistor max acceptable voltage
• - average input current
• - magnetizing inductance of the transformer
• - leakage inductance of the transformer
• - transistor peak voltage, spec from datasheet

## Transistor snubber design

Leakage inductance

It is not easy to calculate the leakage inductance of a transformer, but it can be measured after the transformer is built, or if a prebuilt transformer is used, it can be obtained from a datasheet. It can be assumed that the leakage inductance is 3% of the magnetizing inductance, . If a transformer is well designed, leakage inductance can be reduced to 1% of the magnetizing inductance.

### RCD snubber

Snubber resistor

To calculate the snubber resistance, , an acceptable max transistor voltage, . You want to select a that has a wide margin from the peak transistor voltage rating specified in its datasheet. It still must be greater than the transistors blocking voltage,  Using this, you can calculate , and    Snubber capacitor Snubber diode

The diode voltage must be able to block voltage a high voltage, 1N4007 tends to work.

### Example

Flyback using the following specifications: #### Calculations

• • • • Select: • • • • • Select: • • Select: ## Schottky snubber design

If you choose to use a schottky diode its a good idea to have a snubber.