Diode - Kickback


Kickback Diode is not a special type of Diode.. it is actually a special type of use case of a diode.


Every Inductive device (e.g, Coil and any kind of inductors) stores electromagnetic energy when the current flows through the device. This stored energy would cause some unwanted problem in a specific situation. Following is an example for this ase. Let's suppose we have a simple circuit as in (A). Now you closed the switch and current from the battery flows through the inductor and some amount of the current is converted into electromagnetic energy and stored in the inductor. If the switch remains closed permanently, this would not cause any serious problem. However, the problem happens when you open the switch. Right after you open the switch, the energy stored at the inductor gets released in the form of current which flows in opposite direction from the original direction and generating a sharp spikes in reverse direction as illustrated in Red plot in (C). This reverse current spike can cause problem (may damage) with other devices in the circuit. The Kickback diode is a diode that is used to cope with this reverse current.



How can a diode remove the problem of reverse current ? The answer is simple. Put a diode in parallel to the inductor that would generate the reverse current as shown below. The important thing you need to notice is the direction of the diode. You have to place the diode in proper direction so that it does not flow the normal current and flow the reverse current only.  The diode used for this purpose is called Kickback Diode.



What would be the most common application for the Kickback diode ? Actually, this question is like 'What is the most common inductor that may generate huge amount of reverse current ?'. The answer is a Motor. As you would know, most of the electric motor has a lot of coils in it to generate magnetic field that is required for motor operation. When you switch off the power circuit to spin the motor, it would generate pretty big reverse current. If the reverse current is too big, it would damage (or gradually deteriate) the motor or other components (e.g, Transistor functioning as the electrical switch on the circuit).