REVERSED_POWER_SUPPLY_PROTECTOR_CIRCUIT

Published:2009/7/17 2:29:00 Author:Jessie | From:SeekIC

This circuit is designed to sense a power-supply output (to other circuitry) and detect a reversed-polarity condition. The circuit consists of a complementary metal-oxide semiconductor (CMOS) decoder (CD4555B), which monitors the output of an external power supply for proper polarity. If the power-supply polarity is incorrect, the CD4555B detects that condition and triggers a 2N5060 SCR (Q1). After triggering, the SCR supplies current to a relay (K1), which, upon activation, changes the external power-supply connections (to the external circuitry) to the correct polarity and illuminates a light-emitting diode (LED) to provide a visual warning of the polarity-reversal condition. After the reversed-polarity condition is remedied, pressing the contact switch (S1) momentarily will reset the circuit to its original state. In its present configuration, the circuit can accommodate standard positive power supplies with dc voltages of +5, +10, + 12, and + 15 V. The decoder was designed to operate at these different voltages. With some modifications, the circuit can monitor and correct anomalous power-supply outputs from +3 V, +28 V, or negative-polarity power supplies, or voltages that are either too high or too low.



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