Flyback Converter Protection Circuit for Safe Resonant Restart
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Solution Overview
Problem
In flyback converters, the resonance current can exceed the safe working current of the auxiliary switch transistor due to high voltage on the capacitor, leading to potential damage during restart after power failure or abnormal conditions.
Innovation Solution
A protection circuit with an active discharge module is introduced to discharge the capacitor before restart, providing a controlled discharge path to reduce the resonance current to safe levels, thereby protecting the switch transistor and enhancing system stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the capacitor voltage is allowed to maintain high amplitude for circuit operation, then the circuit can function normally with sufficient voltage drive, but the resonance current will exceed the safe working current of the auxiliary switch transistor when restarted
Solution Approach 1:
The patent applies preliminary action by detecting the abnormal state (capacitor voltage) before restart and actively discharging the capacitor in advance. The detection circuit monitors capacitor voltage, and when abnormal high voltage is detected, the control circuit activates the discharge module to reduce capacitor voltage to a safe level before allowing restart, preventing excessive resonance current that would damage the auxiliary switch transistor.
2Reliability
If the capacitor is discharged before restart to reduce resonance current, then the switch transistor is protected from damage, but the circuit requires additional discharge control circuitry and time delay
Solution Approach 1:
The patent merges multiple functions into integrated circuits to reduce overall complexity. The detection circuit, control circuit, and discharge module are combined into a unified protection system. The detection circuit monitors capacitor voltage, the control circuit processes the detection signal and generates control signals, and the discharge module executes discharge - all working together as an integrated protection mechanism that, while adding components, provides comprehensive protection with coordinated operation.
Solution Approach 2:
The control circuit serves as an intermediary between the detection circuit and the discharge module. It receives detection signals indicating abnormal capacitor voltage, processes this information, and generates appropriate control signals to activate the discharge module. This intermediary role allows intelligent decision-making about when discharge is needed and coordinates the discharge timing to ensure safety while maintaining system functionality.
3Reliability
If a discharge path is provided for the capacitor, then the resonance current can be reduced to safe levels, but the discharge path must be disconnected during normal operation to maintain capacitor functionality
Solution Approach 1:
The discharge path is designed to be dynamic rather than static. The discharge module includes controllable switches that dynamically connect or disconnect the discharge path based on system state. During normal operation, the discharge path is disconnected to maintain capacitor functionality. When abnormal high voltage is detected, the control circuit activates the discharge module, dynamically connecting the discharge path to reduce capacitor voltage, then disconnects it again after discharge is complete.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The active discharge module effectively reduces the resonance current to safe levels during restart, protecting the auxiliary switch transistor and improving the reliability and safety of the flyback converter.
Implementation Method 1
a first capacitor and a first inductor forming a resonance circuit when the second switch transistor is turned on
Implementation Method 2
an active discharge module, connected to at least one end of the first capacitor to provide the discharge path
Data Source
AI summary
Disclosed is a protection circuit of a flyback converter and a control method. The protection circuit comprises: an active discharge module, connected to at least one end of a first capacitor in a resonance circuit of the flyback converter to provide a discharge path, and controlling turning-on and turning-off of the discharge path according to the discharge enable signal; in a normal work state, the discharge path is disconnected, the first capacitor works as a resonance capacitor; before the flyback converter is restarted, the discharge path is turned on for a predetermined time period to release charges of the first capacitor, a resonance current after the flyback converter is restarted is reduced to a safe work current of the second switch transistor. Charges stored in the first capacitor can be discharged to release before the flyback converter is restarted to reduce the resonance current and enhance system stability and security.