Synchronous Rectifier Control With Anti-Accidental Turn-On
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Solution Overview
Problem
Flyback switching power supply systems experience significant conduction and reverse recovery losses due to traditional secondary rectifier diodes, leading to efficiency reductions, especially in applications with large output currents.
Innovation Solution
Incorporation of a synchronous rectification control circuit with an anti-accidental turn-on circuit and light-load detection circuit to prevent accidental turn-ons and optimize power management, utilizing a sampling circuit, turn-on and turn-off comparison circuits, and a drive control circuit to control the switching state of a power switch transistor based on sampling voltage and turn-on enable signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a traditional secondary rectifier diode is used, then the circuit structure is simple, but conduction loss and reverse recovery loss are large, reducing efficiency
Solution Approach 1:
The patent changes the key parameter of the rectifier component from a diode to a MOS transistor with extremely low on-resistance. This parameter change enables synchronous rectification, where the MOS transistor is controlled to conduct during the rectification phase, dramatically reducing conduction loss compared to traditional diode rectification. The low on-resistance of the MOS transistor is the critical parameter that enables this efficiency improvement.
Solution Approach 2:
The patent introduces dynamic control of the rectifier MOS transistor through synchronous rectification control. The transistor is dynamically switched on and off based on the rectification cycle, allowing optimal conductivity during the rectification phase. This dynamic operation enables the system to achieve low loss rectification while maintaining circuit simplicity through controlled switching behavior.
2Loss of energy
If a MOS transistor with extremely low on-resistance is used as the rectifier, then efficiency is improved, but accidental turn-on may occur
Solution Approach 1:
The patent implements preliminary action by requiring multiple conditional checks before enabling the rectifier MOS transistor. The control circuit evaluates several parameters including the primary side current status, voltage differential across the transformer winding, and timing relationships before generating the turn-on signal. This preliminary verification prevents accidental turn-on by ensuring all necessary conditions are met before activation.
Solution Approach 2:
The patent employs feedback mechanisms where the control circuit continuously monitors the primary side current, transformer winding voltage, and rectifier transistor state. This feedback allows the system to detect abnormal conditions that could lead to accidental turn-on and adjust the control signals accordingly. The feedback loop ensures reliable operation by maintaining proper timing and voltage differential conditions.
3Loss of energy
If synchronous rectification control circuit is continuously active, then rectification efficiency is maintained, but power consumption increases during light-load conditions
Solution Approach 1:
The patent implements dynamic load detection that continuously monitors the primary side current to determine load conditions. When light-load conditions are detected, the system dynamically adjusts the rectifier control strategy, allowing the rectifier MOS transistor to enter a dormant or reduced-activity state. This dynamic adaptation enables the system to maintain high efficiency during heavy loads while reducing power consumption during light-load operations.
Solution Approach 2:
The patent employs periodic sampling of the primary side current to detect light-load conditions. By periodically checking the current status and comparing it against threshold values, the system can identify when the load is light and switch to a power-saving mode. This periodic detection mechanism allows the system to alternate between active rectification and dormant states based on actual load requirements.
Data Source
AI summary
Synchronous rectification control circuit and switching power supply system are provided. The circuit includes a samplingcircuit, a turn-on comparison circuit, a turn-off comparison circuit, a drive control circuit, an anti-accidental turn-on circuit, wherein the sampling circuit has a first terminal coupled to a first output terminal of a transformer; the anti-accidental turn-on circuit has a first input terminal coupled to a second terminal of the sampling circuit; the turn-on comparison circuit has a first input terminal coupled to the second terminal of the sampling circuit, a second input terminal coupled to an output terminal of the anti-accidental turn-on circuit; the turn-off comparison circuit has an input terminal coupled to the second terminal of the sampling circuit; the drive control circuit has a first input terminal coupled to an output terminal of the turn-on comparison circuit, a second input terminal coupled to an output terminal of the turn-off comparison circuit.