Protecting MIDI Solutions Relays from Back EMF Generated by Inductive Loads

When switching external loads with MIDI Solutions relays there is the potential for back EMF to be generated. Back EMF arises whenever current is removed from an inductive load (such as a coil in a larger relay or solenoid). The inductive load resists the sudden change in current and produces a reverse voltage which can result in sparking across the contacts of the relays of the MIDI Solutions product, causing them to stick or even causing permanent damage if the spark is large enough. The solution is to add a diode across the load in the opposite direction that the current normally flows, so that when back EMF voltage begins to build it is immediately shunted by the diode. Most common diodes and rectifiers will work, e.g. 1N4001, 1N4002, 1N400x, etc.

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