Isolated Converter Control Interlock for Cross-Conduction Prevention
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Solution Overview
Problem
Existing isolated switching-mode converters face challenges in preventing cross-conduction between primary and secondary-side circuits, which can lead to safety and reliability issues due to false turn-on of synchronous rectifier transistors.
Innovation Solution
A control circuit and method that includes a primary-side controller and a secondary-side controller, where the secondary-side controller transmits an inquiry signal to the primary-side controller, and upon receiving a feedback signal indicating the primary transistor switch is off, the secondary-side controller turns off the synchronous rectifier transistor, ensuring it is off before the primary transistor switch is turned on.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional isolated switching-mode converters are used with synchronous rectifier transistors, then conversion efficiency is improved, but cross-conduction between primary and secondary-side circuits may occur causing safety and reliability issues
Solution Approach 1:
The control circuit performs preliminary actions by detecting the turn-off state of the primary transistor switch before enabling the synchronous rectifier transistor. The controller detects whether the primary transistor switch is turned off, and only then generates the control signal to turn on the synchronous rectifier transistor. This preliminary detection and sequencing prevents cross-conduction while maintaining efficient synchronous rectification.
Solution Approach 2:
The control circuit implements feedback by continuously monitoring the state of the primary transistor switch and using this information to control the synchronous rectifier transistor. The controller detects the turn-off state of the primary transistor switch and feeds this information back to the control logic, which then appropriately controls the gate signal to the synchronous rectifier transistor, preventing cross-conduction while enabling efficient operation.
2Reliability
If interlocking control is implemented to prevent cross-conduction, then safety and reliability are improved, but control circuit complexity increases
Solution Approach 1:
The control circuit merges the cross-conduction prevention function with the existing switching control logic in a single integrated controller. The controller combines the detection of primary transistor switch state, the timing control of synchronous rectifier transistor, and the overall switching sequence management into one unified control unit, reducing the need for separate complex interlocking circuits while maintaining reliable cross-conduction prevention.
Data Source
AI summary
A control circuit and method for an isolated switching-mode converter are disclosed. In the control circuit, before preparing to turn on a primary transistor switch in a primary-side circuit, preferably, a secondary-side controller transmits an inquiry signal to a primary-side controller, and the primary-side controller transmits, after confirming that it has been prepared, a feedback signal to the secondary-side controller to allow the secondary-side controller to turn off a synchronous rectifier transistor based on the feedback signal. After that, the primary-side controller turns on the primary transistor. In other words, in the control circuit and method of the present invention, in preparation for turning on the primary transistor switch, information exchange is conducted between the primary and secondary sides to make sure that the primary transistor switch is turned on after the synchronous rectifier transistor is turn off.