Provides overload and short-circuit protection for load while isolating malfunctioning circuit from other loads on common supply bus. In normal operation, Q1 is saturated. When load attempts to draw more than this saturation value, base current of Q1 cannot maintain saturation so voltage across unmarked resistor drops and current through Q1 drops

correspondingly. When load is shorted, Q2 goes off and short-circuit current folds back to safe lower value. Choose value of unmarked resistor to ensure saturation of Q1 at load current. -S. T. Venkataramanan, Simple Circuit Isolates Defective Loads, EDN Magazine, Jan. 20, 1978, p 114.

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