Valley Lock Switching Control Circuit for Power Converter Loss Reduction
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Solution Overview
Problem
Switching operations in switching power converters generate significant switching losses and electromagnetic interference (EMI) due to the high-frequency operation of switching devices, which are not effectively minimized by existing technologies.
Innovation Solution
A switching control circuit coupled to a switching device and an auxiliary winding of a transformer, comprising a valley detecting circuit, a valley lock circuit, and a pulse width modulation (PWM) circuit, which detects and responds to reflected voltage signals to optimize switching timing and minimize switching losses and EMI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the switching device operates at high frequency to reduce converter size and weight, then the power converter achieves size and weight reduction, but switching losses and EMI increase significantly
Solution Approach 1:
The control circuit performs preliminary detection of the voltage valley point before triggering the switching device to turn on. By detecting when the drain-source voltage reaches its minimum value in advance, the circuit ensures that the switching device is activated at the optimal moment, enabling soft switching and minimizing switching losses while maintaining high-frequency operation for compact size
2Volume of moving object
If the switching device operates at high frequency to reduce converter size and weight, then the power converter achieves size and weight reduction, but EMI increases significantly
Solution Approach 1:
The control circuit performs preliminary detection of the voltage valley point before triggering the switching device to turn on. By detecting when the drain-source voltage reaches its minimum value in advance, the circuit ensures that the switching device is activated at the optimal moment, enabling soft switching and minimizing switching losses while maintaining high-frequency operation for compact size
3Device complexity
If conventional switching control is used without valley detection, then the control circuit is simpler, but switching losses and EMI are not minimized
Solution Approach 1:
An auxiliary winding is introduced as an intermediary element to sense the reflected voltage and generate a detectable signal. This auxiliary winding couples the primary and secondary sides, allowing the control circuit to detect the voltage valley point through the reflected voltage signal without directly measuring the switching device voltage, thus achieving soft switching with moderate circuit complexity
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 enables efficient switching by detecting valley voltages and adjusting switching signals to reduce switching losses and EMI, enhancing the overall efficiency of the switching power converter.
Implementation Method 1
A reflected voltage signal VR (not shown) is generated in the primary winding NP of the transformer T1 in accordance with an output voltage VO across an output capacitor CO 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 for a switching power converter is provided. The switching control circuit is coupled to a switching device and an auxiliary winding of a transformer. The switching control circuit includes a valley detecting circuit, a valley lock circuit, and a PWM circuit. The valley detecting circuit is coupled to receive a reflected voltage signal from the auxiliary winding of the transformer for outputting a control signal in response to the reflected voltage signal. The valley lock circuit is coupled to receive the control signal for outputting a judging signal in response to the control signal during a first period and a second period following the first period. The PWM circuit outputs a switching signal in response to the judging signal.