Synchronous Rectifier Pulse Generator for Flyback Converter
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Solution Overview
Problem
Existing synchronous rectifying circuits for power converters face inefficiencies due to propagation delay in switching signal detection and phase-locking, and additional power consumption from ESR of output capacitors, especially in both continuous and discontinuous modes of operation.
Innovation Solution
A synchronous rectifying circuit that generates pulse signals based on the rising and falling edges of the switching signal, using a pulse generator and isolation device like a pulse transformer or capacitors to control the power switch, eliminating the need for current sense devices and phase-lock circuits, and limiting the maximum on-time of the power switch through a maximum on-time circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If synchronous rectifier is applied on the secondary side of the transformer, then conversion efficiency is improved, but propagation delay in switching signal detection and phase-locking degrades the performance
Solution Approach 1:
The pulse generator produces leading-edge and trailing-edge pulse signals in advance based on the switching signal from the primary side, before the actual switching occurs on the secondary side. This preliminary action eliminates the need for real-time detection and phase-locking, thereby reducing propagation delay while maintaining synchronization for efficient rectification.
2Loss of energy
If switching signal detection and phase-locking are implemented, then synchronous rectifier performance is improved, but additional power consumption occurs
Solution Approach 1:
The invention extracts and eliminates the power-consuming components of switching signal detection and phase-locking circuits. Instead of implementing these complex functions, the pulse generator directly produces the necessary pulse signals from the primary side switching signal, removing the source of additional power consumption while maintaining rectifier performance.
3Ease of operation
If current sense device is used for switching current detection, then synchronous rectifier operation is facilitated, but additional power consumption by ESR of output capacitor occurs
Solution Approach 1:
The invention removes the current sense device and its associated ESR power losses. The pulse generator produces appropriate pulse signals to control the synchronous rectifier operation without requiring switching current detection, thereby eliminating the power consumption caused by the ESR of the output capacitor while maintaining ease of operation.
4Adaptability or versatility
If phase-lock circuit and current sense are required, then synchronous rectifier operation in continuous and discontinuous modes is facilitated, but device complexity increases
Solution Approach 1:
The pulse generator is designed to universally produce the necessary pulse signals for both continuous and discontinuous modes of operation without requiring separate phase-lock circuits or current sense devices. This multi-functional approach simplifies the overall circuit architecture while maintaining adaptability to different operating modes.
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 solution enhances the efficiency of power converters by reducing power consumption and eliminating the need for additional circuitry, achieving higher efficiency in both continuous and discontinuous modes without current sense devices or phase-lock circuits.
Implementation Method 1
An isolation device, such as a pulse transformer or capacitors, is coupled to the pulse generator to transfer the pulse signal from the primary side of the transformer to the secondary side of the transformer
Implementation Method 2
An isolation device, such as a pulse transformer or capacitors, is coupled to the pulse generator to transfer the pulse signal from the primary side of the transformer to the secondary side of the transformer
Data Source
AI summary
A synchronous rectifying circuit is provided for flyback power converter. A pulse generator is utilized to generate a pulse signal in response to a leading edge and a trailing edge of a switching signal. The switching signal is used for switching the transformer of the power converter. An isolation device such as pulse transformer or small capacitors is coupled to the pulse generator for transferring the pulse signal through an isolation barrier of a transformer. A synchronous rectifier includes a power switch and a control circuit. The power switch is connected in between the secondary side of the transformer and the output of the power converter for the rectifying operation. The control circuit having a latch is operated to receive the pulse signal for controlling the power switch.