flyback diode

A diode used in this way is called a flyback diode.

In figure 2, a flyback diode was added in antiparallel with the solenoid.

It features common-cathode flyback diodes for switching inductive loads.

The 'flyback diode' D1 must be a fast recovery type and be capable of carrying the peak inductor current.

Few packages, like L9110, have built-in flyback diodes for back EMF protection.

The voltage across the inductor will merely be a function of the forward voltage drop of the flyback diode.

The remaining 'big' parts, aside from the three inductors already covered, are the switching transistor TR1 and the flyback diode D1.

During the "off" time, the armature's inductance causes the current to continue through a diode called a "flyback diode", in parallel with the motor.

In these images we observe classic signs of back EMF and its elimination through the use of a flyback diode (1N4007).

Flyback diodes are used whenever inductive loads are switched off by silicon components: in relay drivers, H-bridge motor drivers, and so on.

That is why in mechanically-switched circuits, the near-instantaneous dissipation which occurs without a flyback diode is often observed as an arc across the opening mechanical contacts.

When the flyback diode is used to simply dissipate the inductive energy, as with a solenoid or motor, cheap 1N4001 and 1N5400 silicon diodes are used instead.

In a standard buck converter, the flyback diode turns on, on its own, shortly after the switch turns off, as a result of the rising voltage across the diode.

To minimise the antenna-like radiation of this electromagnetic energy from wires connected to the inductor, the flyback diode should be connected as physically close to the inductor as practicable.

When used with a DC coil relay, a flyback diode can cause delayed drop-out of the contacts when power is removed, due to the continued circulation of current in the relay coil and diode.

Usually the source terminal of the N-MOSFET is connected to the cathode of a recirculation diode allowing for efficient management of stored energy in the typically inductive load (See Flyback diode).

A flyback diode solves this starvation-arc problem by allowing the inductor to draw current from itself (thus, "flyback") in a continuous loop until the energy is dissipated through losses in the wire, the diode and the resistor (Figure 3).

In an ideal flyback diode selection, one would seek a diode which has very large peak forward current capacity (to handle voltage transients without burning out the diode), low forward voltage drop, and a reverse breakdown voltage suited to the inductor's power supply.

There are a few preliminaries to be seen to before the construction can begin; these are the winding of inductors L1, L2, L3 and the mounting details of the switching transistor TR1 and the flyback diode D1 on small heatsinks which attach directly to the board.