OVER_UNDERVOLTAGE_PROTECTOR

Published:2009/7/17 2:26:00 Author:Jessie | From:SeekIC

The ICL7665 over/undervoltage detector manufactured by Maxim (IC1) monitors the line voltage and disconnects the load if the input voltage goes below 95 V or above 130 V. The over/under-voltage detector (IC1) monitors the filtered, unregulated dc voltage developed across C5, which changes with the input line voltage. The input voltage levels to IC1 are set by resistors R2 through R8. As long as the voltage at pin 3 is above 1.3 V and the voltage at pin 6 is lower than 1.3 V, both outputs (pins 1 and 7) are low and RY1 is turned on and its contacts are closed. The average line voltage varies at different locations. Trimmer potentiometer R4 provides a small adjustment range so that you can set the window's center for your particular line voltage. When IC1 detects an overvoltage at pin 3, it immediately opens the relay by sending a high output to pin 2 of NOR gate IC3-a, which, in turn, turns off Q1. When IC1 detects an overvoltage at pin 6, the output at pin 7 goes high. Monostable multivibrator IC2 provides a 1/2-s delay to keep RY1 turned off long enough for the voltage across C5 to return to normal. When pin 7 of IC1 goes high, it triggers IC2, and the high output at pin 6 of IC2 causes the output of NOR gate IC3-a to go low, which turns Q1 off and deenergizes RY1. Switch S2 lets you quickly check the circuit's operation at any time. Pushing S2 raises the voltage at the junction of R2 and R5 and turns RY1 off. RESET switch S1 restores normal operation. Switch S1 turns the circuit on initially. An LM7805 voltage regulator (IC4) provides a constant 5-V supply for the integrated circuits and the relay control current.



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