Switching Control Circuit for Soft Switching Power Converters
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Solution Overview
Problem
Switching power converters face inefficiencies due to switching losses and electromagnetic interference (EMI) caused by the switching operation of the switching device, which are not effectively minimized by existing technologies.
Innovation Solution
A switching control circuit that detects the valley voltage across the switching device using a reflected voltage signal from an auxiliary winding of a transformer, allowing for soft switching by turning on the switching device during the valley voltage period and adjusting the off-time based on load magnitude to enhance efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the switching device is turned on during hard switching operation, then the power converter can operate at high frequency, but switching losses and EMI are generated
Solution Approach 1:
The control circuit performs preliminary detection of the reflected voltage signal to identify the valley voltage timing before initiating the switching device turn-on action. This preliminary detection enables the system to prepare for soft switching by timing the gate signal to arrive precisely when the drain voltage reaches its minimum, thereby eliminating switching losses while maintaining high-frequency operation
2Speed
If the switching device is turned on during hard switching operation, then the power converter can operate at high frequency, but EMI is generated
Solution Approach 1:
The control circuit performs preliminary detection of the reflected voltage signal to identify the valley voltage timing before initiating the switching device turn-on action. This preliminary detection enables the system to prepare for soft switching by timing the gate signal to arrive precisely when the drain voltage reaches its minimum, thereby eliminating EMI generation while maintaining high-frequency operation
3Loss of energy
If the switching device is turned on during valley voltage, then switching losses and EMI are minimized, but complex control is required to detect valley voltage timing
Solution Approach 1:
The patent introduces an auxiliary winding on the transformer as an intermediary element that provides a reflected voltage signal proportional to the drain voltage. This intermediary signal serves as a simplified proxy for the actual switching node voltage, enabling valley detection without requiring direct access to the high-voltage switching node. The reflected voltage signal can be directly coupled to the control circuit through resistive dividers, eliminating the need for complex isolation circuits while accurately indicating valley voltage timing
Solution Approach 2:
The auxiliary winding creates a scaled copy of the drain voltage waveform through the reflected voltage signal. This copy waveform replicates the valley voltage timing characteristics and can be safely processed by the control circuit using simple resistive voltage dividers and comparators, avoiding the need for complex high-voltage sensing circuits while maintaining accurate valley detection capability
4Loss of energy
If the switching device is turned on during valley voltage, then switching losses and EMI are minimized, but delay time control is required to achieve precise timing
Solution Approach 1:
The control circuit employs feedback by continuously monitoring the reflected voltage signal and using its state to control the timing of the gate signal. The propagation delay circuit is dynamically adjusted based on the detected valley voltage timing, creating a closed-loop system that automatically synchronizes the switching device turn-on with the minimum voltage point. This feedback mechanism eliminates the need for fixed or manually tuned delay values, simplifying the overall timing control while achieving precise soft switching
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 achieves soft switching and high efficiency for switching power converters across various load conditions, minimizing switching losses and EMI while optimizing energy usage.
Implementation Method 1
A reflected voltage signal VR is generated in the primary winding NP of the transformer T1 in accordance with the output voltage VO and the turn-ratio of the transformer T1
Implementation Method 2
The parasitic capacitor CQ and the primary winding inductor (not shown) of the transformer T1 develop a resonant tank, wherein its resonant frequency fR can be shown as equation (1)
Data Source
AI summary
A switching control circuit is coupled to a switching device and an auxiliary winding of a transformer, wherein a primary winding of the transformer is coupled to the switching device. The switching control circuit includes a voltage receiver, a comparing unit and a propagation delay circuit, wherein the voltage receiver is coupled to the auxiliary winding of the transformer for receiving a reflected voltage signal and transforming the reflected voltage signal into a peak voltage signal, while the switching device is turned off. The comparing unit is coupled to the voltage receiver for receiving the peak voltage signal and a first threshold voltage, and outputting a comparison result. The propagation delay circuit is coupled to the comparing unit for receiving the comparison result, and outputting a PWM signal to turn on the switching device after a delay time.