Negative-voltage-limiting protection circuit for semiconductor chip - performs rapid clamping of input voltage at transistor saturation value without restricting range of circuit protected

摘要

Between the positive and negative DC supply connections (a,b) a protective circuit is constituted by eight inversely driven n-p-n transistors (T4-T11), a resistance (R1) and two p-n-p current sources (Q1,Q2). Interference at the input connection (c) which goes below the negative supply voltage diverts the current (12) from one source (Q2), cutting-off one transistor (T7). Current (I1) from the other source (Q1) flows to the base of another transistor (T5) whose emitter current reverse-drives the input transistor (T11) and clamps the input connection (c). ADVANTAGE - Disturbing voltages are held significantly below breakdown voltage of substrate diode at input connection.