Resonant Switch Control Using Zero-Crossing for Lower Switching Loss
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Solution Overview
Problem
Conventional flyback converters experience high switching loss due to hard-switching mode, limiting their application in high-power and miniaturized electronics as switching frequency increases, which is not effectively addressed by existing soft switching techniques.
Innovation Solution
A control circuit for a resonant circuit with high-side and low-side switches that employs zero-voltage-switching (ZVS) and zero-current-switching (ZCS) techniques by controlling the switches based on specific timing and voltage/current conditions, such as zero-crossing detection and pre-charge periods, to minimize switching loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If switching frequency is increased to enable miniaturization and lightweight design, then productivity and power density are improved, but switching loss increases due to hard-switching mode
Solution Approach 1:
The patent applies preliminary action by pre-charging the resonant capacitor before the main switching event. The low-side switch is turned on first to charge the resonant capacitor through the resonant inductor, creating zero-voltage conditions before the high-side switch operates. This preparatory charging action eliminates voltage spikes and reduces switching losses when the switching frequency is increased.
Solution Approach 2:
The patent implements periodic action through resonant oscillation. The resonant circuit naturally oscillates at its resonant frequency, creating periodic current and voltage waveforms. By synchronizing the switch control with this periodic resonant behavior, the system achieves zero-voltage switching at appropriate moments in the oscillation cycle, enabling high-frequency operation with minimal switching loss.
2Device complexity
If conventional hard-switching mode is used, then device complexity is reduced, but switching loss increases and limits high-power application
Solution Approach 1:
The patent introduces an intermediary resonant circuit consisting of a resonant inductor and resonant capacitor between the input voltage and the switches. This resonant tank circuit acts as a mediator that transforms the abrupt hard-switching operation into smooth zero-voltage switching. The resonant circuit absorbs and releases energy in a controlled manner, eliminating voltage spikes and reducing switching losses while maintaining reasonable device complexity.
3Loss of energy
If soft switching technique is implemented, then switching loss is reduced, but device complexity and control difficulty increase
Solution Approach 1:
The patent applies self-service by utilizing the natural resonant oscillation of the LC circuit to automatically create zero-voltage switching conditions. The resonant circuit self-regulates the timing of voltage and current waveforms, eliminating the need for complex external control circuits to detect and respond to switching conditions. The system uses its own resonant characteristics to achieve soft switching, reducing overall control complexity.
Solution Approach 2:
The patent changes the operating parameters by introducing resonant frequency as a key parameter. Instead of operating at arbitrary switching frequencies, the system is designed to operate at or near the resonant frequency of the LC circuit. This parameter change transforms the switching behavior from hard-switching to soft-switching, reducing losses while the resonant frequency itself becomes the primary control parameter rather than requiring complex timing control.
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 reduces switching loss by ensuring zero-voltage or zero-current conditions during switch on/off, enabling efficient operation at higher frequencies and potentially higher power applications.
Implementation Method 1
resonant operation... LLC resonant topology... resonant inductor and the resonant capacitor... resonance period
Implementation Method 2
An end of the first pulse of the low-side switch control signal corresponds to a time when a voltage across a resonant capacitor of the resonant circuit crosses zero from positive to negative
Implementation Method 3
transformer of the resonant circuit... primary winding and a secondary winding
Data Source
AI summary
A control circuit for a resonant circuit having a high-side switch and a low-side switch is disclosed. The control circuit includes a low-side switch control circuit. The low-side switch control circuit provides a low-side switch control signal for controlling the low-side switch. The low-side switch control signal has a first pulse associated with a first on-time period of the low-side switch. An end of the first pulse of the low-side switch control signal corresponds to a time when a voltage across a resonant capacitor of the resonant circuit crosses zero from positive to negative.