Low Forward Voltage Drop Passive Full-Bridge Rectifier
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Solution Overview
Problem
Isolated power converters face challenges in achieving efficient power transfer and reducing electromagnetic interference (EMI) due to small transformer inductance and resonant capacitance, which affects performance and efficiency, especially in high-power applications.
Innovation Solution
The implementation of a rectifier circuit with diode-connected transistors and a switch network in an isolation power converter, utilizing a transformer to convert DC voltage, and incorporating resonant capacitance to enhance power transfer and reduce EMI, including the use of low voltage threshold transistors to minimize power loss and leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional full-bridge rectifier with diodes is used, then the circuit is simple to implement, but the forward voltage drop causes power loss and reduces efficiency
Solution Approach 1:
The patent changes the operating parameters of the rectifier by replacing diodes with transistor switches that can be actively controlled. The transistor's on-resistance is much lower than the diode's forward voltage drop, especially at higher current levels. This parameter change enables the circuit to maintain low voltage drop across a wide operating range, significantly reducing power loss while keeping the circuit relatively simple.
Solution Approach 2:
The invention introduces dynamic control of the rectifier switches through synchronous rectification. The switches are turned on and off in synchronization with the transformer secondary voltage, allowing the circuit to adapt its operation to the instantaneous voltage and current conditions. This dynamic operation enables the rectifier to maintain optimal efficiency across varying load conditions, unlike static diode-based rectifiers.
2Power
If the transformer inductance is reduced for high-power applications, then the transformer size and cost are reduced, but the resonant capacitance becomes small which affects power transfer efficiency and increases EMI
Solution Approach 1:
The synchronous rectifier dynamically adjusts its switching timing and duration based on the instantaneous voltage and current waveforms. This dynamic operation allows the circuit to maintain high power transfer efficiency even with small transformer inductance by optimizing the conduction period of each switch to match the resonant characteristics of the secondary side circuit, including the parasitic capacitance.
Solution Approach 2:
The rectifier circuit is designed to handle a wide range of operating conditions and power levels using the same basic topology. The synchronous rectification technique works effectively whether the transformer has large or small inductance, making the circuit universally applicable to both low-power and high-power applications without requiring fundamental design changes.
3Loss of energy
If synchronous rectification is implemented to reduce power loss, then power transfer efficiency improves, but the device complexity increases due to additional control circuitry
Solution Approach 1:
The synchronous rectifier uses the transformer secondary voltage and current waveforms themselves to generate the switching control signals. The rectification process inherently provides the timing information needed to control the switches, eliminating the need for external control circuitry. This self-service approach reduces device complexity while maintaining the power loss reduction benefits of synchronous rectification.
Solution Approach 2:
The patent uses the transformer secondary winding and its associated parasitic capacitance as an intermediary to generate the control signals for the rectifier switches. The resonant oscillation of the secondary side circuit naturally produces the timing references needed for synchronous switching, acting as a mediator between the power processing function and the switching control function.
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 improves power transfer efficiency and reduces EMI, enabling effective operation in both high and low power applications by optimizing transformer performance and resonant capacitance, while maintaining low power loss and leakage current.
Implementation Method 1
A galvanic isolation barrier is a transformer, which has two inductors—a primary coil for the input and a secondary coil for the output—and there is no direct electrical connection between the primary and secondary cons
Implementation Method 2
a first diode-connected transistor coupled to a first voltage terminal and a second diode-connected transistor coupled to a second voltage terminal
Data Source
AI summary
A rectifier circuit includes a first diode-connected transistor coupled to a first voltage terminal and a second diode-connected transistor coupled to a second voltage terminal. A switch network is coupled between the first diode-connected transistor and the second diode-connected transistor. The switch network has a first switch network terminal adapted to be coupled to a first terminal of a secondary winding of a transformer and has a second switch network terminal adapted to be coupled to a second terminal of the secondary winding of the transformer.