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Fast Acting Electronic Circuit Breakers

Fast Acting Electronic Circuit Breakers

The circuit breakers on this page make use of the Zetex – ZXCT1009 “High Side Current Monitor’ integrated circuit. The circuits have variable trip current settings and are designed for low current applications.
Two circuit breaker designs are shown; The first has its power isolation device on the Low or common side of the circuit while the second has it isolation device on the High or supply side of the circuit. Both designs use MOSFET devices to isolate the suppiy from the load.

The overload detection and trip system is completely electronic and therefore has a very fast response time (1/120th of a second or less for a full wave DC supply). This allows the load to be disconnected almost instantaneously when an over current condition is detected.


Very – Basic Operation Of Both Circuit Breakers

1. As the current through RSENSE increases the voltage across resistors ROUT – MAX and ROUT – ADJ increases proportionally.

2. When the voltage at the MINUS input of IC 2A rises above the voltage at the PLUS input its OUTPUT will go LOW.

3. When the OUTPUT of IC 2A goes LOW it causes the Flip-Flop formed IC 2B to change states, producing a LOW condition at it’s OUTPUT.

4. Depending on the circuit used, a LOW at the output of IC 2B causes the Gate of Q1 or the Input Terminal of IC 3 to go LOW. This will cause Q1 or IC 3 to turn OFF and open the circuit.

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