Latching relays are also called “keep”, “impulse” or “stay” relays. It has two relaxed states – bistable. It is bistable because when current is switched off, it remains in its last state. This can be achieve by two methods.
1. A solenoid operating a ratchet and cam mechanism.: The first pulse to the coil turns the relay on and the second pulse turns it off
2. By having two opposing coils with an over-center spring or permanent magnet to hold the armature and contacts in position while the coil is relaxed : a pulse to one coil turns the relay on and a pulse to the opposite coil turns the relay off. This type of relay has the advantage that one coil consumes power only for an instant, while it is being switched, and the relay contacts retain this setting across a power outage.
Latching relays are widely used because conventional relays need constant supply of voltage or power but latching relays dont.
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