AHB Half-Bridge Control Using Secondary-Side Turn-Off Timing
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Solution Overview
Problem
Existing half-bridge control circuits in Asymmetric Half Bridge converters face challenges in accurately determining the turn-off time of switching tubes due to sampling errors and complex volt-second balance circuits, which are difficult to adapt to dynamic conditions and varying power ranges.
Innovation Solution
A half-bridge control circuit that includes a primary controller unit and a secondary controller unit connected through an isolated communication unit, allowing the secondary controller to determine the turn-off time of the second switching tube based on the current zero-crossing time of the synchronous rectifier tube, and send a turn-off signal to the primary controller for precise timing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the primary controller uses Zero Current Detection (ZCD) of the auxiliary winding to detect excitation and demagnetization processes and calculates zero-crossing time through internal calculation, then the turn-off time can be determined, but sampling errors make it difficult to accurately calculate the turn-off time and the volt-second balance circuit becomes complex
Solution Approach 1:
The patent introduces an intermediary mechanism (volt-second balance circuit) that directly provides the zero-crossing time signal to the primary controller, eliminating the need for complex internal calculations based on sampling. This intermediary circuit translates the transformer's magnetic state directly into a usable timing signal, resolving the contradiction between measurement accuracy and circuit complexity.
Solution Approach 2:
The volt-second balance circuit serves itself by automatically generating the zero-crossing time signal based on the transformer's inherent magnetic characteristics. The circuit uses the transformer's own voltage and time characteristics to produce the timing signal without requiring external intervention or complex processing, thereby simplifying the overall control system while maintaining accuracy.
2Adaptability or versatility
If a fixed turn-off time is set inside the primary controller, then the control is simple, but it is difficult to accurately match for applications in different power ranges and dynamic compensation is difficult to achieve
Solution Approach 1:
The patent implements a dynamic turn-off time determination mechanism where the primary controller receives real-time zero-crossing time signals from the volt-second balance circuit. This allows the turn-off time to automatically adapt to different power ranges and operating conditions without requiring complex compensation algorithms or multiple fixed settings, achieving versatility while keeping the control logic relatively simple.
Solution Approach 2:
The system incorporates feedback through the volt-second balance circuit, which continuously monitors the transformer's magnetic state and provides updated zero-crossing time information to the primary controller. This feedback mechanism enables automatic adaptation to different power ranges and loading conditions, resolving the contradiction between adaptability and complexity.
Data Source
AI summary
A half-bridge control circuit, an Asymmetric Half Bridge Converter (AHB), a device, and a method are provided. The half-bridge control circuit includes a primary controller unit, an isolated communication unit, and a secondary controller unit, wherein the primary controller unit is configured to drive a first switching tube and a second switching tube to conduct in different time periods, and the secondary controller unit is configured to drive a synchronous rectifier tube to conduct or turn off; in one switching cycle, the secondary controller unit is configured to determine a turn-off time of the second switching tube, and send a first turn-off signal to the primary controller unit through the isolated communication unit at the turn-off time; and the primary controller unit is configured to control the second switching tube to turn off in response to the first turn-off signal.