Undervoltage Detector
The described circuit utilizes an operational amplifier (op-amp) configured as a voltage comparator. The zener diode D1 plays a critical role in establishing a reference voltage, which determines the threshold at which the output state changes. In this case, with D1 rated at 5.6 V, the op-amp is designed to trigger a high output when the input supply voltage dips to approximately 11 V.
To achieve this functionality, the operational amplifier's non-inverting input is connected to the zener voltage, while the inverting input is connected to a voltage divider formed by R3 and another resistor. The resistor R3 is essential for setting the reference voltage, and its value can be modified to fine-tune the trip point. By replacing R3 with an 820 kΩ resistor in series with a 470 kΩ potentiometer, the user can adjust the voltage at the inverting input, allowing for a variable trip point. This configuration provides flexibility in applications where the supply voltage may fluctuate, enabling the circuit to maintain functionality by responding to changes in supply levels.
The output of the op-amp can be connected to various downstream components, such as a relay, indicator LED, or any control circuitry that requires a signal when the supply voltage falls below the specified threshold. This circuit is particularly useful in battery-operated devices or systems where maintaining a minimum voltage is critical for operation. Overall, the combination of the zener diode and adjustable resistors provides a robust mechanism for voltage monitoring and control. The output goes high when the supply falls below a value determined by zener diode Dl. If Dl is a 5.6-V zener, the op amp will switch high when the supply voltage falls below approximately 11 V. The precise trip point can be varied by replacing R3 with an 820-ki) resistor in series with a 470-KOhmhm potentiometer.
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