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Single-coil latching relay drivers

Posted: 16 Sep 2010     Print Version  Bookmark and Share

Keywords:latching relay  relay drivers  memory 

A single-coil latching relay is a relay with memory, usually with a magnetic structure that provides two stable positions for the armature that holds the movable contacts. The force holding the armature in these stable positions is provided by a permanent magnet. An application of electrical current to the relay coil moves the armature from one position to the other, which in turn changes the contact positions.

Applying to the coil a current pulse in one direction, of longer duration than the minimum specified for that relay type, sets the relay to the first of two stable positions, and it remains in that position after the current ceases to circulate. Current in the opposite direction resets the relay to the other position, which is also stable with no current. The relay then remains in that position indefinitely, until a new current pulse toggles it to the other position.

The electronic circuitry needed to drive one of these relays from logic signals can be a half bridge, if dual supply voltages are available, or a full bridge (an "H" type power driver) if only a single supply voltage is available. The use of these bridge topologies is imposed by the need to generate reversible current pulses through the 2-terminal coil. Because the relay itself does not consume power under static conditions, the driving circuitry should also consume minimal power under the same conditions.

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