In recent years, the high-voltage power supply industry in China has experienced rapid growth, with a significant improvement in production quality. As a critical component of these systems, the protection circuit holds great potential for development. The protection circuit plays a vital role in safeguarding internal components, ensuring the safety of both the high-voltage power supply and connected electrical equipment. It helps extend the lifespan of these devices and, more importantly, provides operators with a safer working environment. Therefore, designing an effective protection circuit is essential and highly important.
The overall circuit structure of a high-voltage power supply is illustrated in the figure below. It consists of six main parts: an auxiliary power supply, an inverter unit, a pulse oscillation control unit, a voltage doubler rectifier unit, a high-voltage measurement unit, and a protection unit. The output voltage of the high-voltage power supply typically exceeds certain thresholds. A well-designed protection circuit is placed between the voltage doubler rectifier unit and the high-voltage measurement unit. This setup not only extends the service life of the system but also prevents damage caused by overvoltage, which could otherwise lead to equipment failure or even personal injury. It's clear that the protection circuit is a crucial element in ensuring safe and reliable operation.
The thyristor-relay overvoltage protection circuit design is shown in the image. The sampling circuit is similar to the one used in the previous control circuit design. The sampled voltage is sent to the non-inverting input of the LM358 comparator. The output of the LM358 is connected to the control pin of the thyristor, which regulates its conduction state. The thyristor’s anode is powered through a relay connected to a 12V source, while the cathode is connected to an LED. The LED’s illumination indicates whether the thyristor is conducting.
The thyristor-relay overvoltage protection circuit mainly comprises a sampling circuit, LM358, thyristor, and relay. The sampling voltage controls both the thyristor’s conduction and the relay’s switch operation. The circuit’s principle is demonstrated in the figure. The relay is powered by 12V, and the inverting input of the LM358 is connected to a 5V reference voltage. The sampling circuit is supplied with a variable DC voltage ranging from 0 to 30V. When the sampling voltage is below 5V, the LM358 outputs a low level, preventing the thyristor from turning on. In this case, the relay does not activate, and the LED remains off. However, when the sampling voltage exceeds 5V, the LM358 outputs a high level, allowing the thyristor to conduct. The relay then activates, and the LED lights up, indicating that the thyristor is on. Once triggered, the thyristor remains in the on state even if the sampling voltage drops below 5V, effectively locking the circuit in place.
In summary, when the DC power supply output exceeds 25V, the sampling voltage surpasses 5V. At this point, the LM358 outputs a high level, which is connected to the thyristor’s control terminal. The thyristor’s anode is connected to 12V via a relay, and its cathode is grounded through an LED. Once the control terminal receives a high signal, the thyristor turns on, the relay activates, and the LED illuminates. This mechanism ensures that overvoltage conditions are quickly addressed, protecting the system and enhancing operational safety.
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