Flyback Soft-Switch Control for Zero-Voltage Turn-On in DCM
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Solution Overview
Problem
In discontinuous conduction mode (DCM), the hard turning-on of the main switch transistor in non-symmetric half-bridge flyback converters results in significant turning-on consumption, which increases with higher switch frequencies.
Innovation Solution
A soft switch control circuit that controls the main switch transistor to conduct at zero voltage by generating a trigger pulse signal from the pre-turning on signal of the main switch transistor, transmitted through an isolation module to the secondary edge, allowing the synchronous rectifying switch transistor to conduct before the main switch transistor, reducing conduction consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the main switch transistor is turned on in DCM mode, then the converter operates in discontinuous conduction mode, but hard turning-on causes significant turning-on consumption
Solution Approach 1:
The patent applies preliminary action by generating a pre-turning on signal that activates the synchronous rectifying switch transistor before the main switch transistor turns on. This preliminary action prepares the circuit in advance, allowing the main switch to turn on when the voltage across it is already reduced to zero, thereby eliminating hard switching losses while maintaining high switch frequency operation
Solution Approach 2:
The patent uses an intermediary mechanism by introducing a control circuit that generates trigger pulse signals based on the pre-turning on signal. This intermediary control system coordinates the timing between the synchronous rectifying switch transistor and the main switch transistor, ensuring proper sequencing that enables soft switching without directly modifying the main switch itself
2Loss of energy
If the synchronous rectifying switch transistor conducts before the main switch transistor, then zero voltage switching is achieved, but additional control circuitry is required
Solution Approach 1:
The patent applies self-service by using the existing pre-turning on signal from the control circuit to automatically generate the trigger pulse signal for the synchronous rectifying switch transistor. The system uses its own internal signals to control the timing sequence, eliminating the need for external complex control mechanisms while achieving zero voltage switching
Solution Approach 2:
The control circuit serves multiple functions: it generates the pre-turning on signal, processes this signal to create the trigger pulse signal, and coordinates the switching sequence of both transistors. By making the control circuit multi-functional, the patent reduces overall system complexity rather than adding separate dedicated circuits for each 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 approach enables the main switch transistor to conduct at zero voltage, reducing conduction consumption and improving system efficiency in DCM or hiccup working modes.
Implementation Method 1
the pre-turning on signal of the main switch transistor, to generate a trigger pulse signal, and the trigger pulse signal is transmitted to the secondary edge by the isolation module
Data Source
AI summary
Disclosed is a soft switch control circuit and a flyback converter, comprising a primary edge part and a secondary edge part, and obtaining a trigger pulse signal according to a pre-turning on signal of a main switch transistor before the main switch transistor is turned on. The trigger pulse signal is transmitted to the secondary edge part by an isolation module to control the switch at a secondary edge circuit to conduct, to reduce source-drain voltage of the main switch circuit of the primary edge, to make the main switch transistor to turn on when the source-drain voltage is near zero voltage. The switch of the secondary edge circuit is a synchronous rectifying switch transistor or a discharge switch transistor connected at two ends of the synchronous rectifying switch transistor.