Flyback Switch Control for Lower EMI and Turn-On Loss
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Solution Overview
Problem
Flyback converters face issues with turn-on loss and Electromagnetic Interference (EMI) due to the hard turning on of the auxiliary switch transistor, which increases stress on the rectifier switch transistor and results in higher turn-on losses and EMI problems, especially in discontinuous conduction mode.
Innovation Solution
A switch control circuit and method that regulate the switching rate of the first switch transistor based on the operating state of the flyback converter, using a driving current regulation circuit to generate a current regulation trigger signal, which adjusts the switching rate to reduce the variation rate of the drain-source voltage across the switch transistor, thereby minimizing EMI and turn-on losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the auxiliary switch transistor is turned on once before the main power transistor to enable zero-voltage switching, then zero-voltage switching is achieved, but the auxiliary switch transistor experiences hard turning on and increased stress on the rectifier switch transistor, leading to higher turn-on loss and EMI problems
Solution Approach 1:
The patent applies dynamics by making the switching rate of the first switch transistor adjustable rather than fixed. The control circuit dynamically changes the switching rate between a first switching rate and a second switching rate based on real-time detection of the drain-source voltage, enabling the system to adapt its switching characteristics to different operating conditions and reduce hard switching effects.
Solution Approach 2:
The patent changes the switching rate parameter of the first switch transistor from a constant value to a variable value. By detecting the drain-source voltage and adjusting the switching rate accordingly (using either the first or second switching rate), the system optimizes the turning on process to reduce voltage variation rate and minimize turn-on losses while maintaining zero-voltage switching capability.
2Reliability
If the auxiliary switch transistor is turned on once before the main power transistor, then zero-voltage switching is enabled, but EMI problems increase due to hard turning on and increased stress on the rectifier switch transistor
Solution Approach 1:
The patent applies dynamics by making the switching rate of the first switch transistor adjustable rather than fixed. The control circuit dynamically changes the switching rate between a first switching rate and a second switching rate based on real-time detection of the drain-source voltage, enabling the system to adapt its switching characteristics to different operating conditions and reduce hard switching effects.
Solution Approach 2:
The patent changes the switching rate parameter of the first switch transistor from a constant value to a variable value. By detecting the drain-source voltage and adjusting the switching rate accordingly (using either the first or second switching rate), the system optimizes the turning on process to reduce voltage variation rate and minimize turn-on losses while maintaining zero-voltage switching capability.
3Reliability
If a pulse is added to turn on the auxiliary switch transistor before the main switch transistor, then zero-voltage switching is achieved, but the stress on the rectifier switch transistor increases
Solution Approach 1:
The patent applies dynamics by making the switching rate of the first switch transistor adjustable rather than fixed. The control circuit dynamically changes the switching rate between a first switching rate and a second switching rate based on real-time detection of the drain-source voltage, enabling the system to adapt its switching characteristics to different operating conditions and reduce hard switching effects.
Solution Approach 2:
The patent changes the switching rate parameter of the first switch transistor from a constant value to a variable value. By detecting the drain-source voltage and adjusting the switching rate accordingly (using either the first or second switching rate), the system optimizes the turning on process to reduce voltage variation rate and minimize turn-on losses while maintaining zero-voltage switching capability.
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 solution effectively reduces the switching stress on the rectifier transistor and minimizes EMI by controlling the switching rate of the first switch transistor, resulting in lower overall conduction losses and improved system performance.
Implementation Method 1
a resonant circuit can be formed by a primary side winding of a transformer, the auxiliary switch transistor, a first inductor and a first capacitor
Data Source
AI summary
Disclosed is a flyback converter, a switch control circuit and a control method thereof. A driving current regulation circuit generates a current regulation trigger signal at active state correspondingly according to an operating state of the flyback converter. A switch control driving unit regulates a driving current of the first switch transistor according to the current regulation trigger signal at active state, thus a variation rate of a drain-source voltage across the first switch transistor is slowed down to a preset range. According to the present disclosure, when it is detected that the flyback converter is operating in discontinuous conduction mode or the drain-source voltage across the first switch transistor is high, a switching rate of the first switch transistor is controlled to avoid the voltage across a rectifier switch transistor on a secondary side of the flyback converter to undergo a large jump, and the system EMI is good.