SMPS Synchronous Rectifier Control With Single-PWM Signal Splitting
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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 increased complexity when replacing them with 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 pulses to ensure non-overlapping switching periods, thereby reducing the burden on the main controller and increasing power handling capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
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 control circuit generates multiple PWM control signals autonomously from a single input signal, enabling the synchronous rectifier to self-regulate without additional external control inputs. This maintains structural simplicity while achieving low-loss operation through active control of switching elements.
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:
Multiple control signals for different switching elements are merged into a single input PWM signal that the control circuit processes internally. The control circuit generates all necessary control outputs from this single input, eliminating the need for multiple independent control signals and reducing overall system complexity.
Solution Approach 2:
The control circuit serves multiple functions: it generates PWM signals for primary switching elements, generates PWM signals for secondary synchronous rectifier elements, and coordinates their operation to prevent shoot-through currents. This multi-functionality consolidates what would otherwise require multiple separate control circuits.
3Reliability
If multiple independent control signals are generated for each switching element, then precise control is achieved, but the controller burden increases and scalability is limited
Solution Approach 1:
The control function is segmented between a central controller that provides a single PWM signal and a distributed control circuit that generates all necessary control outputs locally. This segmentation allows the central controller to maintain simple operation while the local control circuit handles the complexity of generating multiple precise control signals for various switching elements.
Data Source
Figure 1
Figure 2~2(viii)
Figure 3
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).