Low Forward Voltage Rectifier Reducing Power Dissipation
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Solution Overview
Problem
Conventional rectifiers in flyback power supplies experience significant power dissipation due to the forward voltage drop of diodes, leading to inefficiencies in energy transfer and increased heat generation.
Innovation Solution
A Low Forward Voltage Rectifier (LFVR) is introduced, comprising a bipolar transistor and a parallel diode with a base current injection circuit, which reduces the forward voltage drop to approximately 0.1 volts by injecting a base current, thereby minimizing power dissipation and improving efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional silicon diode is used for rectification, then the rectifier structure is simple, but the forward voltage drop is high (approximately 1.0 volts) causing significant power dissipation
Solution Approach 1:
The patent combines a bipolar transistor and a diode into a single integrated rectifier device. The bipolar transistor's collector-emitter path is placed in parallel with the diode, creating a composite rectifier structure that leverages both components' characteristics to reduce power dissipation while maintaining rectification functionality
Solution Approach 2:
The bipolar transistor serves multiple functions: it acts as a low-voltage-drop rectifier element during forward conduction, provides base current injection control, and works in conjunction with the diode to achieve both voltage reduction and rectification in a single device structure
2Loss of energy
If the forward voltage drop is reduced to approximately 0.1 volts through base current injection, then power dissipation is minimized, but the device complexity increases due to additional circuit components
Solution Approach 1:
The base current injection circuit is designed to automatically provide the necessary base current to the bipolar transistor during operation. The circuit uses the existing current flow through the device to generate and inject the required base current, eliminating the need for external control circuits and reducing overall system complexity
Solution Approach 2:
The patent changes the operating parameters of the bipolar transistor by injecting base current, which fundamentally alters the collector-emitter voltage characteristics from the conventional 0.7-1.0 volts down to approximately 0.1 volts, achieving the desired power dissipation reduction
3Loss of energy
If a bipolar transistor with base current injection is used, then the forward voltage drop is reduced to approximately 0.1 volts, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The bipolar transistor and diode are manufactured as a single integrated device structure, sharing common semiconductor layers and processing steps. This integration simplifies manufacturing by eliminating the need to assemble separate components and reduces fabrication complexity despite the enhanced functionality
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 flyback converters compared to conventional silicon diodes, enhancing power supply efficiency and allowing for minimal design changes by replacing conventional diodes with a two-terminal TO-247 package.
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 Low Forward Voltage Rectifier (LFVR) includes a bipolar transistor, a parallel diode, and a base current injection circuit disposed in an easy-to-employ two-terminal package. In one example, the transistor is a Reverse Bipolar Junction Transistor (RBJT), the diode is a distributed diode, and the base current injection circuit is a current transformer. Under forward bias conditions (when the voltage from the first package terminal to the second package terminal is positive), the LFVR conducts current at a rated current level with a low forward voltage drop (for example, approximately 0.1 volts). In reverse bias conditions, the LFVR blocks current flow. Using the LFVR in place of a conventional silicon diode rectifier in the secondary of a flyback converter reduces average power dissipation and increases power supply efficiency.