Power Converter Cross-Conduction Detection for SR Protection
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Solution Overview
Problem
Switch mode power converters face efficiency losses due to cross conduction events, which occur when both the primary and secondary switches are conducting, leading to potential damage and reduced duty cycle range, despite measures like dead time insertion to prevent cross conduction.
Innovation Solution
A cross conduction detector circuit is integrated into the power converter to monitor the forward node voltage, detecting when the primary switch is conducting and disabling the secondary switch to prevent cross conduction, using threshold comparisons and control logic to ensure efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dead time is increased to prevent cross conduction, then switch protection is improved, but power converter efficiency deteriorates and duty cycle range is reduced
Solution Approach 1:
The patent implements dynamic dead time adjustment where the dead time period is not fixed but varies based on operating conditions. The control circuit monitors the state of switches and dynamically modifies the dead time duration to prevent cross conduction only when necessary, thereby maintaining efficiency during normal operation while providing protection when cross conduction risks arise.
Solution Approach 2:
The patent employs feedback mechanisms where the control circuit continuously monitors switch states and operating conditions, then adjusts the dead time accordingly. This closed-loop approach allows the system to respond to actual cross conduction risks rather than using a conservative fixed dead time, optimizing both protection and efficiency.
2Reliability
If dead time is increased to prevent cross conduction, then switch protection is improved, but duty cycle range is reduced
Solution Approach 1:
By making the dead time dynamic rather than fixed, the patent allows the duty cycle range to be maximized at each operating point. The dead time is adjusted in real-time based on switch states and load conditions, enabling the converter to maintain full adaptability across different duty cycles while still providing cross conduction protection when needed.
3Loss of energy
If cross conduction detection and prevention is implemented, then converter efficiency is maintained, but device complexity increases
Solution Approach 1:
The patent implements a self-service cross conduction detection mechanism where the control circuit utilizes existing switch state information and operating parameters already available in the power converter. The system monitors itself using existing sensors and control signals, eliminating the need for additional complex detection hardware while maintaining efficiency through intelligent control algorithms.
Data Source
AI summary
A control system for a power converter having an energy transfer element, a power switch, and a synchronous rectifier (SR). The control system includes an SR control circuit and a cross conduction detector circuit. The detector circuit receives an SR signal indicating whether the synchronous rectifier has been turned on using a drive signal output by the SR control circuit.Based on the SR signal, the detector circuit determines whether the synchronous rectifier is conducting. The detector circuit also compares a voltage at a forward node of the energy transfer element to a threshold voltage to determine whether the power switch is conducting. The detection circuit disables the synchronous rectifier in response to detecting a cross conduction event, based on a determination that the synchronous rectifier and the power switch are both conducting during a time interval in which the synchronous rectifier is turned on.