Isolated Converter Control Circuit for Primary-Side Turn-On Interlock
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Solution Overview
Problem
Existing isolated switching-mode converters face challenges in preventing common conduction between the primary-side and secondary-side circuits, which can occur due to false turn-on of the synchronous rectifier transistor in the secondary-side circuit, compromising safety and reliability.
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, which then provides a feedback signal to keep the synchronous rectifier transistor turned off, and the primary-side controller turns on the primary transistor switch only after the synchronous rectifier transistor is turned off, ensuring synchronized operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional isolated switching-mode converter is used, then the converter can operate with simple control, but there is a risk of common conduction between primary-side and secondary-side circuits due to false turn-on of the synchronous rectifier transistor
Solution Approach 1:
The secondary-side controller sends an inquiry signal to the primary-side controller before the primary transistor switch turns on. The primary-side controller responds with a feedback signal indicating whether the synchronous rectifier transistor is safely turned off. This preliminary action ensures that the primary transistor switch only turns on after confirming the secondary-side transistor is off, preventing common conduction while maintaining controlled complexity through structured signal exchange.
2Productivity
If the synchronous rectifier transistor is turned on without verification, then the converter can achieve continuous operation, but common conduction may occur compromising safety
Solution Approach 1:
The primary-side controller provides feedback signal to the secondary-side controller regarding the state of the synchronous rectifier transistor. The secondary-side controller uses this feedback to determine whether to turn on the primary transistor switch. This feedback mechanism ensures continuous operation while preventing common conduction by making the turn-on decision dependent on verified safe conditions.
3Reliability
If interlocking control is implemented to prevent common conduction, then safety is improved, but the control mechanism becomes more complex
Solution Approach 1:
The patent uses inquiry signals and feedback signals as intermediaries between the primary-side controller and secondary-side controller. These signal exchanges mediate the interlocking control by conveying state information and control decisions without requiring direct complex interconnection. The intermediary signals simplify the control mechanism while maintaining safety through structured communication between controllers.
Data Source
AI summary
A control circuit and method for an isolated switching-mode converter are disclosed. In the control circuit, in preparation for turning 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 confirm that the primary transistor switch has been turned off. 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 turned off.