Over-Voltage Protection (OVP) in AC-DC Converters

Editorial Team - everything PE

Jul 19, 2023

When the voltage applied across the terminal of a device exceeds its normal/expected range, it is referred to as over-voltage. In AC-DC converters, over-voltage occurs due to voltage transients, power surges, load fluctuations, or faults within the system. Over-voltage volatility can lead to accelerated aging, insulation breakdown, component failure, or even catastrophic damage to electrical equipment.

Importance of Over-Voltage Protection

  • Equipment Protection: Over-voltage protection safeguards sensitive components, such as semiconductors, capacitors, and integrated circuits, from excessive voltage levels that could cause immediate or long-term damage. By limiting the voltage to safe levels, the protection measures ensure the longevity and reliability of these components.
  • System Stability: Over-voltage can disrupt the stability of the electrical system, leading to malfunctions, abnormal operation, or even design shutdown. By mitigating over-voltage risks, the protection mechanisms maintain system stability and uninterrupted power supply.
  • Safety Assurance: Over-voltage can pose safety hazards, such as electric shocks or fire risks. The implementation of over-voltage protection measures helps to minimize these risks, ensuring the safety of users and preventing potential accidents.

Over-Voltage Protection Techniques

Voltage Clamping: Voltage clamping is a commonly used technique to limit the voltage level within a safe range. This method involves the use of protective devices, such as varistors or transient voltage suppressors (TVS), which provide a low-impedance path to divert excessive voltage away from the protected circuit. These devices exhibit a high resistance under normal operating conditions and a low resistance during over-voltage events, effectively clamping the voltage to a predetermined level.

Voltage Regulation: Voltage regulation techniques aim to maintain a stable output voltage within the desired range by continuously monitoring and adjusting the converter's operation. Feedback control mechanisms, such as voltage regulators, are employed to sense the output voltage and regulate it by adjusting the converter's input or switching parameters. By closely regulating the output voltage, these techniques prevent over-voltage conditions.

Voltage Regulation in Full Wave Rectifier

Crowbar Protection: Crowbar protection is an effective method to safeguard AC-DC converters from over-voltage events. It involves the use of a crowbar circuit, consisting of a thyristor or a triac, which is triggered to short-circuit the input voltage during an over-voltage condition. By creating a low-resistance path, the crowbar circuit diverts excessive voltage away from the converter and protects the system components.

Surge Arresters: Surge arresters, also known as lightning arresters, are employed to protect AC-DC converters from high-energy transients caused by lightning strikes or switching surges in the power grid. Surge arresters divert the transient energy to the ground, preventing it from reaching the converter and other sensitive equipment. These devices are typically connected in parallel to the converter input to provide a low-impedance path for the transient currents.

Input Filters: Input filters are commonly used to attenuate high-frequency noise and voltage spikes that can cause over-voltage conditions. These filters consist of passive components, such as inductors and capacitors, that are placed at the input of the converter. They help to smooth out voltage fluctuations and suppress high-frequency interference, ensuring a clean and stable input voltage for the converter. By reducing the amplitude of voltage spikes, input filters contribute to over-voltage protection.

Circuit Breakers and Fuses: Circuit breakers and fuses are essential protective devices that help prevent over-voltage conditions caused by faults or short circuits. Circuit breakers are designed to automatically interrupt the circuit when a fault is detected, whereas fuses are sacrificial elements that melt and open the circuit under excessive current conditions. By interrupting the circuit, these devices protect the converter and the system from over-voltage events that can result from faults.

Click here to learn more about Over-Current Protection (OCP) in AC-DC Converters.

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