Solid_state_circuit_breaker

Published:2009/7/24 4:18:00 Author:Jessie | From:SeekIC

This circuit is the solid-state equivalent of a circuit breaker. The circuit turns off the main regulator output within 700 ns of an overload using the values shown. The trip current and breaker-delay point are settable over a wide range. Under normal operation, current through the 1-Ω shunt is insufficient to bias Q1 into conduction. Q2 is also off and the regulator produces an output. When an overload occurs (Trace A of Fig. 9-4B is the regulator output current), the potential across the 1-Ωresistor rises, turning on Q1. This drives the Q2 base (trace B), and turns Q2 on, grounding the enable pin (trace C) to shut down the regulator output (trace D). The 10-kΩ values from the main output to the pin latch the regulator down. The 1-Ω value can be changed to accommodate other desired current-trip points. The 4.7-μ.F capacitor (in dashed lines) can be added (delete the 100-pF capacitor) for applications where fast response is not desired.



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