AC voltage regulators play a crucial role in ensuring the stable operation of power equipment. Their overvoltage and undervoltage protection functions must balance real-time performance, reliability, and interference immunity. When the input voltage exceeds the rated range, the protection circuit must quickly cut off the power supply or trigger an alarm to prevent equipment damage. This function relies on three core components: voltage detection, comparison and judgment, and execution control. These components work together to form a complete protection system.
Voltage detection is the foundation of the protection function. Its core lies in converting AC voltage into a processable DC signal. The input voltage is first stepped down to a safe range by a transformer, then rectified by a rectifier bridge to convert AC to pulsating DC, and finally smoothed by a filter capacitor to output a stable DC voltage. This DC voltage is proportional to the input AC voltage and serves as the reference signal for subsequent comparisons. Some designs incorporate linear optocouplers or voltage transformers to achieve electrical isolation, preventing high-voltage side interference from affecting the control circuit and improving system safety.
The comparison and judgment stage needs to accurately identify voltage anomalies, typically using a window comparator composed of dual comparators. One comparator sets an overvoltage threshold, outputting a high level when the detected voltage exceeds this value; the other sets an undervoltage threshold, outputting a high level when the voltage falls below this value. Within the normal voltage range, both comparators output a low level. The two signals are integrated using an AND gate, outputting a control signal only when the voltage is abnormal, driving the subsequent actuator. To avoid malfunctions caused by voltage fluctuations, a hysteresis design can be introduced, giving the comparators different thresholds during voltage rise and fall, forming a "hysteresis" range and enhancing anti-interference capability.
Execution control is the final step in the protection function, and its design must balance response speed and reliability. When the voltage is abnormal, the control signal output by the logic circuit drives a transistor or MOSFET to conduct, thereby energizing the relay coil. The relay contacts open, cutting off the main circuit power supply, achieving overvoltage or undervoltage protection. Some designs use solid-state relays or thyristors instead of mechanical relays to improve switching speed and lifespan. Simultaneously, after the protection action is triggered, the system can be equipped with an alarm indicator light or buzzer to prompt the user to handle the fault promptly.
In overvoltage protection scenarios, when the input voltage suddenly increases due to a power grid fault or load change, the DC voltage output by the detection circuit rises accordingly. Once the overvoltage threshold is exceeded, the comparator outputs a high level, which, after logic processing, drives the relay to quickly cut off the power supply. This process must ensure that the relay contact capacity is sufficient to prevent arcing; simultaneously, the protection circuit should have a self-locking function to prevent secondary damage caused by reconnection after a brief voltage drop.
Undervoltage protection addresses situations where the voltage is too low, such as insufficient power supply from the mains or excessive line voltage drop. When the detected voltage falls below the undervoltage threshold, the comparator outputs a high level, triggering the relay to disconnect. This design prevents equipment from operating under low voltage, avoiding faults such as motor stalling and capacitor overheating due to excessive current. Some AC voltage regulators also delay power restoration after undervoltage protection triggers, waiting for the voltage to stabilize before reconnecting, preventing frequent start-stop cycles from affecting equipment lifespan.
In practical applications, the protection circuit must consider environmental adaptability. High temperature, high humidity, or strong electromagnetic interference environments may affect component parameters, leading to threshold drift or malfunction. Therefore, sufficient margins should be allowed in component selection, and shielding and filtering measures should be adopted to improve anti-interference capabilities. Simultaneously, the protection circuit should be calibrated regularly to ensure accurate thresholds and prevent protection failures due to component aging. Through multi-stage collaborative design, the overvoltage and undervoltage protection functions of the AC voltage regulator can effectively improve the stability and safety of power equipment operation.
