Flyback Converter Rectifier With Base Current Injection
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Solution Overview
Problem
Conventional flyback converters experience significant power dissipation in rectifier diodes, leading to inefficiencies due to high forward voltage drops, which reduce the overall efficiency of the power supply.
Innovation Solution
The implementation of a Low Forward Voltage Rectifier (LFVR) using a Reverse Bipolar Junction Transistor (RBJT) and a distributed diode integrated circuit, which injects base current to maintain the transistor in saturation, resulting in a substantially lower forward voltage drop of approximately 0.1 volts, reducing conduction losses and increasing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional rectifier diode is used in the flyback converter, then the circuit structure is simple, but the forward voltage drop is high (approximately 1.0 volt) resulting in significant power dissipation (approximately 15 Watts)
Solution Approach 1:
The patent changes the operating parameters of the bipolar transistor by injecting base current to maintain saturation, thereby reducing the collector-emitter voltage drop from the typical 0.7-1.0 volt to approximately 0.1 volt. This parameter change directly reduces power dissipation while maintaining the two-terminal device structure, resolving the contradiction between energy loss and device complexity
Solution Approach 2:
The patent introduces a base current injection circuit as an intermediary component that supplies current to the base terminal of the bipolar transistor. This intermediary mechanism enables the transistor to operate in saturation mode, achieving low voltage drop without requiring a completely different device structure, thus reducing power dissipation while keeping the overall circuit relatively simple
2Loss of energy
If a bipolar transistor is used as the rectifying element with base current injection, then the forward voltage drop is reduced to approximately 0.1 volts, but the device structure becomes more complex requiring base current injection circuitry
Solution Approach 1:
The patent extracts the base current injection function into a separate, dedicated circuit module that is specifically designed to supply the required base current. This extraction allows the main rectifying element (bipolar transistor) to focus on its primary function of current conduction with low voltage drop, while the complexity of base current management is handled by a specialized auxiliary circuit, thereby reducing conduction loss while organizing device complexity into functional modules
3Loss of energy
If the bipolar transistor is maintained in saturation mode through base current injection, then the voltage drop across the rectifying element is minimized, but additional current path components are introduced
Solution Approach 1:
The patent merges the base current injection circuit with the existing flyback converter circuitry by utilizing available circuit nodes and components. The base current is drawn from the same power supply nodes that already exist in the converter, and the injection circuit is integrated into the existing current paths. This merging approach minimizes the addition of separate current paths while still achieving saturation mode operation, thereby reducing voltage drop without significantly increasing current path complexity
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
The LFVR significantly reduces average power dissipation in the rectifying component, enhancing the efficiency of the flyback converter power supply by minimizing voltage drops across the rectifying element, thereby improving overall power supply efficiency.
Implementation Method 1
The base current injection circuit injects a base current into the bipolar transistor in forward bias conditions (conditions in which the voltage on the first package terminal is greater than the voltage on the second package terminal)
Implementation Method 2
The parallel diode is coupled between the collector and the emitter of the bipolar transistor so that the anode of the diode is coupled to the collector and the cathode of the diode is coupled to the emitter
Data Source
AI summary
A flyback converter involves a bipolar transistor (BJT) and a parallel-connected diode as the rectifying element in the secondary side of the converter. The transformer of the converter has a primary winding, a first secondary winding, and a second secondary winding. A first end of the first secondary winding is coupled to the BJT base. A first end of the second secondary winding is coupled to the BJT collector and to the anode of the diode. The first and second secondary windings are wound such that when primary winding current stops, pulses of current flow out of the first ends of the first and second secondary windings. These currents are such that the BJT is maintained in saturation throughout at least most of the time current flows through the rectifying element, thereby achieving a low forward voltage across the rectifying element, reducing conduction loss, and increasing converter efficiency.