Electronic circuitry to protect solid state switches from excessive locked-rotor current in appliances

The locked-rotor current in washing machines can destroy a triac before the circuit breaker has time to trip. The design of electronic circuitry to sense the overload condition and turn off the triac before damage results is presented. The protection circuits feature programmable response time, automatic resetting, and low cost. Data on the prototype circuit are given, and a computer simulation is used to compute component values. Critical triac device parameters are discussed, and their effect on protection circuit design is evaluated