Inductor Voltage Spike

Inductor voltage spike is the sharp rise in voltage that occurs across an inductor when the current flowing through it is suddenly interrupted or changed rapidly.  This phenomenon is due to the fundamental property of an inductor, which resists changes in current.

Explanation

Inductors store energy in the form of a magnetic field when current passes through them.  If the current through the inductor changes very quickly (such as when a switch is opened or a circuit is interrupted), the rate of change of current becomes very large, and as a result, the voltage across the inductor can spike dramatically.

Key Points about Inductor Voltage Spike

Energy Release  -  The energy stored in the inductor's magnetic field must be released when the current stops, which causes the spike.
Switching Circuits  -  Voltage spikes are common in circuits where inductors are used, such as relays, motors, or transformers.  For example, when turning off a relay, the inductive kickback can generate high voltage.
Protection  -  To prevent damage to circuits from these voltage spikes, components such as diodes (often called flyback diodes) are used to safely dissipate the energy.

Example

In a DC motor, when the power is suddenly switched off, the inductance of the motor’s windings causes a large voltage spike.  Without protective measures, this spike could damage other sensitive components in the circuit.

 

Inductor Voltage Spike Formula
\( V \;=\;   L \; (  \Delta I \;/\; \Delta t ) \)     (Inductor Voltage Spike) \( L \;=\;   V \; \Delta t \;/\; \Delta I  \) \( \Delta I \;=\;   V \; \Delta t \;/\; L  \) \( \Delta t \;=\;   L \; \Delta I \;/\; V  \)
Symbol	English	Metric
\( V \) = Inductor Voltage Spike	\(V\)	\(kg-m^2 \;/\; s^3-A\)
\( L \) = Inductance	\(H\)	\(kg-m^2\;/\;s^2-A^2\)
\( \Delta I \) = Current Change	\(I\)	\(C \;/\; s\)
\( \Delta t \) = Time Change	\(sec\)	\(s\)