How to drive a latching relay

Latching relay (a.k.a. impulse relay) can be turned on and off by momentarily applying a voltage across the relay coil. The relay would maintain in its last switched state without the need to maintain the coil current. In this post, I will show a simple circuit which can be used to drive such relays. In the video towards the end, I also included more explanations and some demonstrations.

How to drive a latching relay

The relay I am using here is a latching RF relay. It is used to switch the input signal between its two outputs. For this particular relay, the input has an APC-7 connector. One side of the output has an N connector and the other side is 50 Ohm terminated. Although this relay is an RF relay, the method I described below is applicable to any latching relays.

Many dedicated ICs (such as MAX4820, MAX4821) can be used for driving such relays. Because of nature of the latching relay, no H-bridge is needed (although you can definitely use an H-bridge, but it would be wasteful). The circuit I have here uses an SN754410 quad H-bridge driver chip. Only one of the four half-bridges is used. In fact, you can pretty much use any circuitry with a push-pull output configuration as long it can provide sufficient impulse current.


For more detail: How to drive a latching relay

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