Products >> Power Management (PMIC) >> Overvoltage protection circuit

An overvoltage protection circuit is used to safeguard electronic devices from damage caused by excessive voltage. In electronic systems, power supply voltages may abnormally increase due to various factors like power fluctuations, lightning strikes, and circuit malfunctions. The overvoltage protection circuit can detect these high voltages and take appropriate measures to prevent damage to sensitive components (such as chips, transistors, capacitors, etc.) in electronic devices, thus prolonging the service life of the equipment and enhancing the reliability of the system.

Working Principle
- Voltage Detection Part:
  - This is the basic part of the overvoltage protection circuit. It is usually implemented using a voltage comparator or a voltage divider. The voltage divider can reduce the input voltage proportionally, and then the divided voltage and a preset reference voltage are input to the voltage comparator. When the divided voltage exceeds the reference voltage, the comparator outputs a signal indicating that an overvoltage condition is detected. For example, in a simple overvoltage protection circuit, if the input voltage is 10V and it is divided by a voltage divider composed of two resistors at a ratio of 1:10 to obtain 1V, and the reference voltage is set to 0.8V, when the input voltage rises above 8V, the comparator will detect the overvoltage.
- Control Part:
  - When an overvoltage signal is detected, the control part initiates the corresponding protection measures. The most common control method is to cut off the power path or shunt the excessive voltage by controlling switching elements (such as relays, MOSFETs, etc.). For example, in some simple circuits, when an overvoltage is detected, the control circuit will cause a relay to disconnect, thereby cutting off the connection between the input power supply and the subsequent circuit to avoid damage to the subsequent circuit from the excessive voltage; or by controlling a MOSFET to conduct, the excessive voltage is guided to a bleeder resistor for energy dissipation.
- Reset Part (Optional):
  - After the overvoltage condition disappears, some overvoltage protection circuits need to be reset so that the system can resume normal operation. The reset operation can be achieved through a manual reset button or an automatic reset circuit. The manual reset button requires the user to press the button to restart the circuit after confirming that the overvoltage condition has disappeared; the automatic reset circuit automatically reconnects the power path when it detects that the voltage has returned to normal, making the system return to the normal working state.
Main Types
- Overvoltage Protection Circuit Based on Zener Diode:
  - A Zener diode can maintain a relatively stable voltage across its terminals when it is in reverse breakdown. In this type of overvoltage protection circuit, the Zener diode is connected in parallel with the protected circuit. When the voltage is normal, the Zener diode is in the cutoff state; when the voltage exceeds its Zener voltage, the Zener diode conducts in reverse breakdown and shunts the excess current to the ground or other appropriate paths, thereby protecting the protected circuit from excessive voltage damage. This circuit has a simple structure and low cost, and is often used in circuits that are more cost-sensitive and have not extremely high voltage requirements.
- Overvoltage Protection Circuit Based on Thyristor (SCR):
  - A thyristor has the characteristic of remaining in the conduction state once it is turned on. In the overvoltage protection circuit, the control electrode of the thyristor is connected to a voltage detection circuit. When an overvoltage is detected, the voltage detection circuit will send a trigger signal to the control electrode of the thyristor to turn it on. After the thyristor is turned on, it will short-circuit or shunt the overvoltage energy to protect the circuit. This circuit has a fast response speed and can quickly and effectively protect the circuit. However, since the thyristor needs certain conditions to turn off once it is turned on, its turn-off mechanism needs to be considered when designing the circuit.
- Overvoltage Protection Circuit Based on Integrated Circuit (IC):
  - There are many specially designed overvoltage protection ICs now. These ICs internally integrate high-precision voltage detection circuits, control circuits, and other auxiliary function circuits. When used, simply connect them correctly between the power supply and the protected circuit to achieve the overvoltage protection function. This circuit has the advantages of high precision, high reliability, and rich functions. For example, some ICs can realize multi-level overvoltage protection, overvoltage alarm and other functions, and are suitable for complex electronic systems with high protection requirements.
Application Fields
- Power Supply Systems:
  - In various power supplies (such as computer power supplies, mobile phone chargers, etc.), the overvoltage protection circuit is essential. It can prevent damage to electronic devices caused by overvoltage due to internal power supply failures or external power fluctuations. For example, in a computer power supply, if the mains input voltage abnormally rises, the overvoltage protection circuit will promptly cut off the power output to protect important components such as the computer motherboard and hard disk.
- Communication Equipment:
  - Communication base stations, routers and other communication equipment need to operate stably for a long time and have high requirements for voltage stability. The overvoltage protection circuit can protect these devices from the impact of overvoltage caused by lightning strikes, grid fluctuations and other factors. In a communication base station, the overvoltage protection circuit can ensure the normal operation of communication equipment in a complex and changeable environment, reducing equipment failures and maintenance costs.
- Industrial Automation Equipment:
  - The electrical environment in the industrial field is complex and the voltage fluctuates greatly. The overvoltage protection circuit in industrial automation equipment (such as PLC, motor driver, etc.) can prevent damage to the equipment caused by overvoltage due to motor starting, stopping or grid failure. This helps improve the reliability and service life of industrial equipment and reduce production interruptions caused by equipment damage.