Flyback Converter Synchronous Rectifier Power Loss Reduction
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Solution Overview
Problem
The existing flyback converters with synchronous rectifiers suffer from significant power losses and reduced efficiency due to the current transformer's losses, such as copper, iron, eddy current, and hysteresis losses, which also shorten the transformer's lifespan.
Innovation Solution
Incorporating a shunt resistor with a much smaller resistance than the current transformer in parallel with it, providing a bypass path for the secondary current, thereby reducing the power loss and enhancing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a current transformer is used in the synchronous rectifier to detect current and initiate rectification, then the synchronous rectification function is achieved, but significant power losses occur due to copper loss, iron loss, eddy current loss and hysteresis loss
Solution Approach 1:
The patent extracts the current detection function from the current transformer by adding a separate detection winding. The main transformer core performs both power transformation and current detection simultaneously, eliminating the need for a separate current transformer and its associated losses.
Solution Approach 2:
The patent makes the flyback transformer multi-functional by adding a detection winding that serves dual purposes: maintaining the magnetic circuit integrity and providing current detection signals for synchronous rectification control, thereby eliminating the separate current transformer.
2Ease of operation
If a current transformer with large turn ratio is used for current detection, then the synchronous rectification control is enabled, but the transformer's lifespan is shortened due to overheating and power losses
Solution Approach 1:
The patent extracts the current detection function from the main power transfer path by using a separate detection winding on the transformer core. This allows current detection without forcing main transformer current through high-impedance paths, reducing heat generation and extending transformer lifespan.
3Measurement precision
If the current transformer is connected in series to detect secondary current, then the current detection accuracy is improved, but the power loss and heat generation increase significantly
Solution Approach 1:
The patent introduces a detection winding as an intermediary element that magnetically couples to the transformer core. This winding provides accurate current detection signals without requiring main transformer current to flow through detection components, thereby maintaining measurement precision while minimizing power loss.
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 configuration significantly reduces power losses and extends the life of the current transformer, leading to improved overall efficiency and stability of the flyback converter.
Implementation Method 1
The current transformer 14 has a primary winding 15 and a secondary winding 16 with a relatively large turn ratio (about 1:100). When the secondary current I2 flows through the primary winding 15, the secondary winding 16 will generate an output signal which is proportional to the current flowing through the primary winding 15.
Implementation Method 2
a shunt resistor connected in parallel with the current transformer for providing a current bypass path to the current flowing through the current transformer. More specifically, the resistance of the shunt resistor is far smaller than the impedance of the current transformer.
Implementation Method 3
when the main switch MS is turned off, the synchronous switch SS is turned on through the secondary synchronous rectification driver 13 so that the energy stored in the primary winding Np11 is transferred to the secondary side of the flyback transformer TF, thereby inducing a high-frequency AC voltage across the second secondary winding Ns12
Data Source
AI summary
Disclosed is a flyback converter with a synchronous rectifier, in which the synchronous rectifier includes a synchronous switch, a current transformer connected in series between a drain terminal of the synchronous switch and an output terminal, and a secondary synchronous rectification driver connected to the gate terminal of the synchronous switch. Furthermore, a shunt resistor is connected in parallel with the current transformer for providing a current bypass path for a secondary current flowing through the synchronous switch and the current transformer, and thereby reducing the current flowing through the current transformer. Thus, the overall efficiency of the flyback converter can be enhanced and the life of the current transformer can be prolonged.