Synchronous Rectification Control Circuit Phase Adjustment
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Solution Overview
Problem
The synchronous rectification type power supply units face challenges in rapid ON and OFF operations due to increased time delay in switching cycles, especially at high frequencies, which can hinder efficient operation of the main and rectification switch devices.
Innovation Solution
A control circuit with a phase difference adjusting portion that detects the status transition of a signal at the connecting point between the main and rectification switch devices, adjusting the output timing of a second signal to minimize phase difference, allowing the rectification switch device to be turned ON synchronously with the main switch device's OFF state, thereby reducing time delay and enhancing switching speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the switching frequency is increased to improve power supply efficiency, then productivity is improved, but time delay in switching cycles increases causing operational challenges
Solution Approach 1:
The control circuit performs preliminary detection of the main switch device's OFF state through voltage detection at the connecting point before triggering the rectification switch device to turn ON. This preliminary action allows the system to anticipate the optimal switching moment, reducing the time delay that would otherwise occur during the switching transition at high frequencies.
2Speed
If the rectification switch device is turned ON immediately when the main switch device turns OFF to reduce time delay, then switching speed is improved, but simultaneous activation of both switches may occur causing short-circuit current
Solution Approach 1:
The control circuit continuously monitors the voltage at the connecting point between the main switch device and rectification switch device. When the main switch device turns OFF, the voltage changes and this feedback signal is detected by the detecting portion, which then triggers the phase difference adjusting portion to control the rectification switch device's ON timing. This feedback mechanism ensures the rectification switch device turns ON only after confirming the main switch device is OFF, preventing simultaneous activation while maintaining fast switching response.
3Measurement precision
If a comparator is used to detect voltage levels for switch control, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The control circuit merges multiple functions into a single integrated structure. The detecting portion, phase difference adjusting portion, and switch control functions are combined in one control circuit unit that processes the voltage signal from the connecting point. This merging approach maintains precise voltage detection capability while reducing overall device complexity compared to using separate comparators and control units for each function.
Data Source
AI summary
The control circuit comprises: a detecting portion COMP1 for detecting a status transition of a first signal FR at the connecting point P which changes at a constant cycle corresponding to current flowing through the antiparallel diode D when the main switch device FET is turned OFF; and a phase difference adjusting portion 30, 40 for adjusting the phase difference by adjusting the output timing of the second signal FP corresponding to a phase difference between the phase of the first signal FR detected by the detecting portion COMP1 and the phase of the second signal FP generated based on the first signal of one cycle before and the rectification switch device FET2 is turned ON corresponding to the second signal FP whose output timing is adjusted by the phase difference adjusting portion 30, 40.