LLC Resonant Circuit Control Using Body Diode Frequency Jitter
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Solution Overview
Problem
Existing LLC resonant converters struggle to reduce harmonic components associated with switching noise, which hinders compliance with EMI standards, especially under light load conditions where the switching frequency remains constant.
Innovation Solution
A method for controlling a resonant circuit by adjusting the conduction time of the body diode in different working periods, causing a change in the switching frequency of the resonant circuit, thereby achieving frequency jitter and reducing switching noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If frequency jitter technology is used to distribute energy within a frequency band, then EMI test requirements are met, but the switching frequency remains constant under light load conditions
Solution Approach 1:
The patent applies dynamics by making the synchronous rectifier switch conduct for a specific duration during each switching period, creating a dynamic body diode conduction period. This dynamic control of the body diode conduction time enables the switching frequency to vary under light load conditions, achieving frequency jitter effect that distributes noise energy across a frequency band, thereby resolving the contradiction between reducing switching noise and maintaining frequency adjustment capability.
Solution Approach 2:
The patent changes the parameter of body diode conduction time to control the switching frequency. By adjusting the body diode conduction period parameter, the switching frequency can be dynamically modified under light load conditions. This parameter change approach enables frequency jitter to reduce harmonic components and switching noise while maintaining adaptability, thus resolving the technical contradiction.
2Object-affected harmful factors
If the body diode conduction time is adjusted to change switching frequency, then frequency jitter is achieved and switching noise is reduced, but control complexity increases
Solution Approach 1:
The patent employs self-service by utilizing the inherent body diode of the synchronous rectifier switch for frequency control purposes. The body diode's natural conduction characteristics are harnessed to generate frequency jitter, eliminating the need for additional dedicated frequency control components or complex control circuits. This self-service approach reduces control complexity while achieving the desired frequency jitter effect to reduce harmonic components.
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 method effectively reduces switching noise by introducing frequency jitter, thereby enhancing compliance with EMI standards, even under light load conditions where traditional frequency jitter technologies are ineffective.
Implementation Method 1
LLC resonant converter
Implementation Method 2
transformer, including a primary winding and a secondary winding
Implementation Method 3
synchronous rectifier switch includes a body diode; adjusting, in different working periods, a conduction time of the body diode
Data Source
AI summary
The present disclosure provides a method for controlling a resonant circuit and a resonant circuit. The resonant circuit to which the method is applicable includes: a primary switching circuit, configured to receive an input voltage; a resonant branch, including a capacitor and an inductor connected in series; a transformer, including a primary winding and a secondary winding, and the resonant branch is connected between the primary switching circuit and the primary winding; and a secondary switching circuit, connected to the secondary winding and configured to provide an output voltage to a load, and the secondary switching circuit includes a synchronous rectifier switch, and the synchronous rectifier switch includes a body diode; the method includes: adjusting, in different working periods, a conduction time of the body diode to cause a switching frequency of the resonant circuit to change.