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Energy-Tripped Circuit Breaker Trips After a Time Interval That Varies as a Function of Sensed Load Current

Energy-Tripped Circuit Breaker Trips After a Time Interval That Varies as a Function of Sensed Load Current

The circuit of this circuit has three distinct parts – circuit breaking, current sensing and timing. The circuit breaking function can be any type of electronically controlled relay or solid state switch, properly sized for voltage and current ratings of the load being protected. Load current sensing is achieved via an LT6108-2 current sense amplifier with built-in comparator. The LT6108-2 converts the voltage drop across a small valued sense resistor to a ground-referenced output voltage that is directly proportional to the load current. The trip threshold is created by scaling the output voltage via resistor divider and feeding the result to the integrated comparator with a precision 400mV voltage reference. The comparator changes state when the load current exceeds the threshold. To prevent short duration transients from causing nuisance trips, an LTC6994-2 Timerblox delay timer is added between the comparator output and the circuit breaker. Once tripped, the comparator falling edge starts a variable time delay interval, which, if allowed to complete, signals the circuit breaker to open. Nothing happens if the transient duration is shorter than the delay.