Latchingreläer

Latchingreläer, commonly called a latching relay or bistable relay, is an electromechanical switch that preserves its contact state after the drive current is removed. Unlike non-latching relays, it only requires power to change state, making it energy efficient for holding a signal or memory bit.

There are two main implementations: single‑coil and dual‑coil. A single‑coil latching relay uses a permanent magnet and the polarity or a brief drive pulse to flip state, after which the magnet holds the armature. A dual‑coil latching relay has separate set and reset coils so either state can be reached by energizing the corresponding coil.

Operation notes: energizing the set coil moves the armature to connect the output contact; energizing the reset coil moves it to the opposite contact. The state remains even with power removed, until another pulse is applied. Some designs rely on a temporary pulse and an external magnet to maintain position; others require a brief current to overcome the hold force. Contact ratings and coil ratings vary, and latching relays can have lower power consumption than non‑latching types in steady state.

Advantages include lower energy consumption for maintaining a state and improved data retention in power‑loss events, which is useful in control systems, portable equipment, and memory‑like circuits. Limitations include higher cost, longer switching times due to mechanical movement, and the need for extra circuitry to drive the set/reset signals.

Common applications are memory and status indication in telecommunications, automotive control units, power supplies, instrumentation, and remote or battery‑powered systems where retained state is desired without continuous power.