Active Clamp Flyback Overvoltage Protection Control
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Solution Overview
Problem
Switching converters, such as active-clamp flyback circuits, face issues with spike voltage generation during over-voltage protection, leading to potential damage of auxiliary switches and secondary diodes due to high loop currents, and existing solutions like large resistors increase no-load power consumption and reduce efficiency.
Innovation Solution
A control circuit is implemented to keep the main switch off and the auxiliary switch operational for a predetermined number of cycles during over-voltage protection, providing a controlled discharge path for the clamp capacitor to prevent damage and reduce no-load losses, without the need for additional discharge circuits like large resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large resistor is added to discharge the clamp capacitor during over-voltage protection, then the clamp capacitor can be discharged, but the no-load power consumption increases and efficiency decreases
Solution Approach 1:
The auxiliary switch serves dual functions: during normal operation it discharges leakage inductance energy, and during over-voltage protection it discharges the clamp capacitor. The existing component performs the protection function without requiring additional dedicated discharge circuitry, achieving self-service and avoiding extra power consumption.
Solution Approach 2:
The auxiliary switch is designed to perform multiple functions across different operating conditions: it provides a discharge path for leakage inductance during normal switching cycles, and provides a discharge path for the clamp capacitor during over-voltage protection events. This multi-functionality eliminates the need for separate discharge circuits.
2Reliability
If the auxiliary switch is turned off during over-voltage protection, then the main switch can be protected, but high loop currents can damage the auxiliary switch and secondary diode
Solution Approach 1:
The control circuit detects over-voltage conditions and activates the auxiliary switch discharge path before the clamp capacitor voltage can rise to dangerous levels. By acting preliminarily, the system prevents the formation of harmful spike voltages and high loop currents that would otherwise damage components.
Solution Approach 2:
The control circuit continuously monitors the output voltage and provides feedback to determine when over-voltage protection is needed. When the output voltage exceeds a threshold, the control circuit activates the auxiliary switch to discharge the clamp capacitor, creating a closed-loop control system that responds to actual voltage conditions.
Data Source
AI summary
An apparatus including: a switching converter having a main switch configured to provide power to a transformer, an auxiliary switch configured to provide a release path for leakage inductance energy of the transformer, and a clamp capacitor coupled in series with the auxiliary switch; and a control circuit configured to control the main switch to be off and the auxiliary switch to operate to discharge the clamp capacitor when in an over-voltage protection mode. A method of controlling the switching converter can include: controlling the main switch to be off; and controlling the auxiliary switch to operate to discharge the clamp capacitor when in an over-voltage protection mode.