Resonant Converter Capacitive Mode Detection via Secondary Winding Voltage
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Solution Overview
Problem
Prior resonant converters with primary side control face challenges in detecting capacitive mode, leading to high power dissipation and switch failure due to reverse recovery issues, which is difficult to apply in secondary side control configurations.
Innovation Solution
A resonant converter design incorporating a square wave generator, resonant network, isolated transformer, voltage detection circuit, capacitive mode judge circuit, and switching frequency controller, where the capacitive mode judge circuit compares voltage detection signals with thresholds to generate a flag signal indicating capacitive mode, and the switching frequency controller adjusts frequencies to prevent capacitive mode operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If primary side control method is used to detect capacitive mode, then power dissipation and switch failure are reduced, but the method is difficult to apply in secondary side control configurations
Solution Approach 1:
The patent inverts the detection approach by moving from primary side control to secondary side control. Instead of detecting capacitive mode at the primary side through current phase detection, the patent detects it at the secondary side by monitoring the voltage across the secondary winding, making the solution adaptable to secondary side control configurations while maintaining switch reliability.
Solution Approach 2:
The patent introduces an intermediary detection mechanism using the secondary winding voltage as a mediator to infer the operational mode. By monitoring the voltage across the secondary winding and comparing it with a threshold, the system can determine capacitive mode without directly measuring primary side current phase, enabling secondary side control adaptability.
2Power
If resonant converter operates in capacitive mode, then voltage transfer is achieved, but high power dissipation and switch failure occur due to reverse recovery
Solution Approach 1:
The patent applies preliminary action by detecting the capacitive mode condition before it causes harmful effects. The detection circuit monitors the secondary winding voltage and generates a flag signal when capacitive mode is detected, allowing the control system to take preventive action (such as adjusting switching frequency or duty cycle) before high power dissipation and reverse recovery issues occur.
Solution Approach 2:
The patent implements feedback by using the detected secondary winding voltage to generate a flag signal that feeds back to the control system. This feedback mechanism enables real-time monitoring and adjustment of operating conditions to prevent the converter from remaining in capacitive mode, thereby reducing power dissipation and avoiding switch failure.
Data Source
AI summary
A method of capacitive mode detection is used in a resonant converter. The resonant converter has a square wave generator having a first switch and a second switch, a resonant network, an isolated transformer having a primary winding and a second winding, and a rectifier network providing an output DC voltage for a load. The method of capacitive mode detection includes: detecting a voltage of the secondary winding and generating a voltage detection signal; detecting an output DC voltage of the rectifier network and generating a voltage detecting threshold; comparing the voltage detection signal with the voltage detection threshold when either of the first and the second switches is turned OFF; generating a flag signal indicating whether the resonant converter enters into a capacitive mode based on the comparison result.