Over-Current Protection (OCP) in AC-DC Converters

Editorial Team - everything PE

Jul 19, 2023

When current flowing through a circuit exceeds its specific/rated limit, it is referred to as over-current. This occurs due to various factors such as short circuits, component failures, excessive load demand, and other external faults. Over-current can lead to excessive heating, voltage drop, elevated stress on system components, and system failure, which can compromise electronic device performance, reliability, and lifespan.

Importance of Over Current Protection

  • Safety: Over-current leads to component damage, electrical arcing, and fire hazards. Robust protection mechanisms are essential to prevent catastrophic failures and ensure the safety of both the converter and the connected devices or systems.
  • Equipment Protection: AC-DC converters are often power-sensitive electronic devices. Over-current can damage these devices, leading to costly repairs or replacements. Adequate protection measures can safeguard the equipment and extend its operational lifespan.
  • System Reliability: Over-current can cause unplanned downtime, system malfunctions, and disruptions to critical processes. By implementing appropriate protection mechanisms, the reliability and availability of the AC-DC converter system can be significantly enhanced.

Over Current Protection Techniques

Current Limiting: Current limiting is a protection technique that restricts the output current to a safe level. This is achieved by utilizing current sensing elements such as shunt resistors, current transformers, or Hall effect sensors. When the sensed current exceeds a predetermined threshold, the converter control circuitry reduces the duty cycle or switches off the converter to limit the output current.

Current limiting in a rectifier

Fuse Protection: Fuses are widely used as a primary line of defense against over-current conditions. A fuse is a sacrificial device that interrupts the circuit when it detects an excessive current. Once the fuse is blown, it needs to be replaced. Fuses are simple, reliable, and cost-effective protection devices.

Circuit Breakers: Circuit breakers are automatic switches that can be manually or electrically controlled. They protect by quickly interrupting the circuit when an over-current event occurs. Unlike fuses, circuit breakers can be reset and reused, making them suitable for applications where manual intervention is not desirable.

Electronic Over Current Protection: Electronic protection methods utilize specialized integrated circuits (ICs) that monitor the current and control the operation of the converter. These ICs can detect over-current events and trigger protective actions, such as reducing the duty cycle, shutting down the converter, or activating a fault alarm.

Current Foldback: Current foldback protection is a technique where the output current reduces as the load impedance decreases. It helps prevent excessive current flow during short circuit conditions, limiting the stress on the converter and the load.

Current Limiting Vs Foldback Technique

Overload Detection and Shutdown: In this technique, the converter monitors the load current continuously. If the current exceeds a predefined threshold for a specific duration, the converter shuts down to protect against prolonged overloads.

Comprehensive Testing and Validation: Thoroughly test and validate the AC-DC converter under various operating conditions to ensure that it operates within the specified current limits. This includes testing for short circuit conditions, overloads, and transient events to verify the effectiveness of the over-current protection mechanisms.

Click here to learn more about Over Voltage Protection in AC-DC Converters.

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