Synchronous Rectifying Control Circuit for Switching Mode Power Supply
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Solution Overview
Problem
Traditional synchronous rectification methods for switching mode power supplies face issues with shoot-through and low reliability, particularly at low voltage applications, due to high power loss and voltage drop in rectifying diodes, and existing control methods like discrete self-driven and single-chip phase-locked loop methods have slow response and reliability issues.
Innovation Solution
A synchronous rectifying control circuit and method that includes an integrating circuit, comparison circuit, and logic circuit to provide a drive signal for a secondary switch, ensuring the switch is turned OFF before the primary switch is ON, thereby preventing shoot-through, and utilizing a threshold signal to manage the switching process effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If traditional rectifying diodes are used in low voltage applications, then the circuit structure is simple, but power loss is high due to high voltage drop
Solution Approach 1:
The patent changes the key parameter from using a passive rectifying diode to using an active MOSFET switch, which has much lower on-resistance and voltage drop at low voltage applications. This parameter change directly reduces power loss while the integrated control circuit manages the increased complexity.
2Reliability
If discrete self-driven method is used for synchronous rectification, then the circuit structure is simple, but response speed is slow and reliability is low
Solution Approach 1:
The patent merges the control functions into a single-chip integrated control circuit that combines phase-locked loop, timing control, and MOSFET drive capabilities. This integration improves reliability by reducing component count and interconnections while providing fast response through unified control architecture.
3Reliability
If single-chip phase-locked loop method is used for synchronous rectification, then control integration is improved, but reliability is low in burst mode
Solution Approach 1:
The patent implements dynamic control that adapts to different operating modes including burst mode. The control circuit dynamically adjusts timing parameters and switch control based on real-time detection of operating conditions, ensuring reliable operation across light load, no load, and heavy load scenarios.
4Ease of operation
If traditional smart rectifier method is used, then response speed is fast, but shoot-through may occur causing safety issues
Solution Approach 1:
The patent uses preliminary action by implementing advance timing control that calculates and executes switch turn-off before the primary switch turns on. The integrated control circuit proactively manages the rectifying MOSFET timing based on detected voltage conditions, preventing shoot-through before it can occur rather than reacting after the problem arises.
Data Source
AI summary
A switching mode power supply comprising a synchronous rectifying control circuit. The synchronous rectifying control circuit comprising an integrating circuit, a first comparison circuit and a logic circuit. The integrating circuit is configured to provide an integrating signal. The first comparison circuit comprises a first input coupled to the output of the integrating signal, a second input configured to receive a first threshold signal, and an output. The logic circuit comprises a first input coupled to the output of the first comparison circuit and an output coupled to a control terminal of the secondary switch, and the secondary switch is configured to be turned OFF when the integrating signal is less then the first threshold signal.