Synchronous Rectifier Control Circuit for Lower SMPS Conduction Loss
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Solution Overview
Problem
Conventional switched-mode power supply (SMPS) topologies face inefficiencies due to the non-negligible threshold voltage of freewheel diodes, leading to significant conduction losses, and the increased complexity of using active, controlled switching elements for synchronous rectification.
Innovation Solution
A control circuit that generates primary and secondary PWM control signals from a single input PWM control signal, allowing for simplified control of switching elements and reducing conduction losses by timing the primary and secondary pulses to ensure efficient operation of the switching elements, thereby reducing the burden on the main controller.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional freewheel diodes are used for rectification, then the circuit structure is simple, but significant conduction losses occur due to non-negligible threshold voltage
Solution Approach 1:
The patent extracts the control function from the main controller and implements it locally in the synchronous rectifier module. This allows the synchronous rectifier to autonomously generate its control signal based on the rectified current waveform, eliminating the need for complex external control while achieving low conduction losses through active switching control
Solution Approach 2:
The synchronous rectifier module monitors its own rectified current waveform and autonomously generates the control signal for its switching element. This self-service mechanism eliminates the need for external control signals, reducing circuit complexity while maintaining the low conduction loss benefits of active control
2Loss of energy
If active controlled switching elements are used for synchronous rectification, then conduction losses are reduced, but control complexity increases due to additional control signals required
Solution Approach 1:
The synchronous rectifier module autonomously generates its own control signal by detecting the rectified current waveform and determining when the current reaches zero. This self-service approach eliminates the need for external control signals from the main controller, reducing control complexity while maintaining low conduction losses
Solution Approach 2:
The control logic continuously monitors the rectified current waveform and uses this feedback to autonomously determine the switching timing. The control signal is generated based on real-time current status, ensuring optimal switching moments while simplifying the overall control architecture
3Reliability
If multiple control signals are generated for multiple switching elements, then each switching element can be controlled precisely, but the burden on the main controller increases
Solution Approach 1:
The control function is extracted from the main controller and relocated to the synchronous rectifier module itself. This distribution of control functions reduces the burden on the main controller, allowing it to focus on primary switching control while the synchronous rectifier autonomously manages its own switching timing
Solution Approach 2:
The control system is segmented into independent control units: the main controller handles primary switching, while each synchronous rectifier module has its own integrated control logic. This segmentation allows parallel operation of multiple rectifier modules without proportionally increasing the main controller's burden
Data Source
AI summary
A control circuit (100) is provided, for controlling switching elements of a switched-mode power supply (10). The control circuit includes a control input (112), for receiving a pulse width modulated, PWM, control signal comprising a series of control pulses. The control circuit has a primary output (120), for controlling a primary switching element of the switched-mode power supply. Also provided are: a synchronous rectifier module (SR) incorporating the control circuit (100); and a switched mode power supply incorporating the synchronous rectifier module (SR).