Synchronous Rectifier MOSFET Control for Flyback Converter Efficiency
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Solution Overview
Problem
Conventional synchronous rectifiers in power converters face limitations such as high cost and complex circuit designs, which are inadequate for meeting the requirements of low voltage, high efficiency, and small form factor in modern power supplies due to their reliance on diode rectification and additional components like current sensors.
Innovation Solution
The implementation of a synchronous rectifier system that detects current across the transformer's secondary winding using a power MOSFET, eliminating the need for additional transformers or hall elements, and integrates the control circuit with the MOSFET into a single IC, simplifying the design and reducing component counts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If diode rectification is used in power converters, then the circuit design is simple, but the power efficiency is low due to excessive forward voltage drop
Solution Approach 1:
The patent changes the operating parameters by using a synchronous rectifier with a power MOSFET instead of a diode. The MOSFET's on-resistance is controlled to be much lower than the diode's forward voltage drop, achieving voltage drop reduction from around 500mV to much lower levels, thereby improving power efficiency while maintaining circuit simplicity
2Loss of energy
If synchronous rectifier with power MOSFET is used, then power efficiency is improved, but the cost and circuit complexity increase
Solution Approach 1:
The patent merges the control circuit and the power MOSFET into a single integrated synchronous rectifier device. This integration eliminates the need for separate control circuits and additional components, reducing circuit complexity while maintaining the high efficiency benefits of synchronous rectification
3Loss of energy
If conventional synchronous rectifier with additional components is used, then power efficiency is improved, but the component count and cost increase
Solution Approach 1:
The patent combines multiple functions into the single synchronous rectifier device, eliminating the need for separate current sensors, additional transformers, and other auxiliary components. This integration reduces the overall component count while maintaining improved power efficiency
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances power conversion efficiency, reduces production costs, and simplifies circuit design, while avoiding secondary current backflow and unnecessary power losses, thereby improving the overall performance of flyback converters.
Implementation Method 1
a voltage difference across the synchronous rectifier to detect a current in a secondary winding of the transformer
Implementation Method 2
an SR uses a power MOSFET to replace the diode
Implementation Method 3
This transformer provides a galvanic isolation between the input and the output
Data Source
AI summary
A synchronous rectification circuit for a power supply includes a power switch for coupling to a secondary winding of a transformer of the power supply and an output capacitor of the power supply. The power switch includes a four-terminal MOSFET having a source, a drain, a gate, and a body. A body diode is formed by a junction between the body and the drain or by a junction between the body and the source. The body diode is coupled in parallel to the source and drain of the power transistor. A control circuit is configured to provide a control signal for controlling an on/off state of the power switch in response to a voltage condition of two terminals of the power switch. When the body diode makes a transition from reverse bias to forward bias, the control circuit causes the MOSFET to turn on, and when the forward bias voltage drops below a reference voltage, the control circuit causes the MOSFET to turn off. When the body diode makes a transition from forward bias to reverse bias, the control circuit causes the MOSFET to turn off.