# How to design a snubber for a flyback converter

*1,796*pages on

this wiki

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.

## VariablesEdit

- - 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 designEdit

- 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 snubberEdit

- 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.

### ExampleEdit

flyback using the following specs.

#### CalculationsEdit

- Select:
- Select: , 5W
- Select: , 500V

## Schottky snubber designEdit

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

- design to be added