Freewheeling(Flyback) Diode

・In Japanese
＜Premise knowledge＞
・Electromagnetic induction
・H bridge circuit

■Basic circuit using Freewheeling Diode

In a circuit using a coil as shown below, when the switch is turned on and the current flows through the coil and then the switch is turned off, the coil tries to keep the current flowing due to Electromagnetic induction and a high voltage is generated instantaneously. This is called flyback voltage or surge voltage. All of this flyback voltage is applied to the switch, causing the switch to fail.



In order to prevent this, the flyback voltage is released by using the following circuit. The diode attached here is called a freewheeling diode.

■Application of freewheeling diode to H-bridge circuit

In the H bridge circuit, a diode is attached in parallel to each switch as shown below, which is also a freewheeling diode. At first glance, it seems that the flyback voltage cannot be prevented when it is connected in parallel with the switch, but this is intended to release the voltage applied to other switches.

■Flywheel diodes?

In Japan, some people refer to freewheeling diodes as flywheel diodes.

Freewheel refers to the mechanism of the drive wheel of a bicycle, which turns by inertia without pedaling, while flywheel refers to the mechanism of an automobile, which uses inertia to reduce the fluctuation of engine rotation. I think both meanings can be used, but freewheel is probably the original meaning in this diode. (Flyback and freewheel are combined to form flywheel?)

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