Optically isolated latching solid state relay with low on resistance and linear operation

摘要

A latching relay includes a supply terminal, a load terminal, first and second coupling circuits, a latch circuit, first and second transistors, and a local supply node coupled to a capacitor. In one example, the supply terminal is coupled to a supply node and the load terminal is coupled to the load. The first and second transistors control the conductivity of a drive transistor coupled to the load. A microcontroller controls the latching relay to switch the load on and off. To enable the load, the microcontroller sinks current from the supply terminal and through the first coupling circuit. While the load is enabled, the capacitor is discharged. The latching relay is operable in a refresh mode in which current is pulsed through the first coupling circuit causing capacitor to be re-charged from the supply terminal. To disable the load, the microcontroller sinks current through the second coupling circuit.