Selection parameters of fast recovery diode for Flyback diode

Selection parameters of fast recovery diode for Flyback diode

How to select a fast recovery diode to replace Flyback diode? Firstly, confirm the parameters of the fast recovery diode.

The withstand voltage of the fast recovery diode is how much voltage can be applied in the reverse direction. You can see that the Flyback diode is connected in the reverse direction in the circuit. For example, in your circuit, if the coil is loaded with 12V, then the directional withstand voltage value of your diode must be greater than 12V. However, the reverse withstand voltage of general fast recovery diodes is very high.

The maximum forward conduction current of the fast recovery diode, for example, the maximum forward conduction current of 1N4148 is 150mA. If your coil current is too high, the Flyback diode will be burned out. So 1N4148 is only suitable for coil protection with low current, such as 5V relays.