LLC Converter Soft Start Using Resonant Tank Current Feedback
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Solution Overview
Problem
LLC converters face challenges in quickly establishing output voltage during the start phase without causing current impulses in the resonant tank, which can damage power switches.
Innovation Solution
A control circuit that detects the current of the resonant tank and generates a second drive signal based on a first drive signal and current thresholds to adjust the power switch operation, turning it off during overcurrent conditions and maintaining the same signal during normal conditions, thereby avoiding current impulses and protecting the LLC converter elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the LLC converter operates with a fixed frequency and fixed duty cycle drive signal during start phase, then the output voltage can be established quickly, but a current impulse is generated in the resonant tank which damages power switches
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed frequency and fixed duty cycle drive signal to a variable frequency and variable duty cycle drive signal during the start phase. The control circuit dynamically adjusts the drive signal parameters based on real-time current detection, allowing the converter to quickly establish output voltage while preventing current impulses that would damage power switches.
Solution Approach 2:
The patent implements feedback by using a control circuit to detect the current in the resonant tank in real-time and use this information to adjust the drive signal parameters. The control circuit generates a drive signal with variable frequency and duty cycle based on the detected current, creating a closed-loop control system that prevents current impulses while maintaining fast start performance.
2Loss of time
If the duty cycle is increased to quickly establish output voltage during start phase, then the start duration is reduced, but a current impulse is generated in the resonant tank
Solution Approach 1:
The patent applies parameter changes by varying both the frequency and duty cycle of the drive signal during the start phase instead of using fixed parameters. The control circuit adjusts these parameters dynamically based on current detection, enabling the converter to establish output voltage quickly while avoiding the generation of current impulses in the resonant tank.
Solution Approach 2:
The patent uses dynamics by making the drive signal parameters (frequency and duty cycle) variable rather than fixed. The control circuit continuously adjusts these parameters during the start phase based on real-time current feedback, allowing the system to achieve fast startup without generating harmful current impulses.
3Reliability
If the frequency is adjusted to prevent current impulse in the resonant tank, then power switch safety is improved, but the start duration is prolonged
Solution Approach 1:
The patent applies parameter changes by simultaneously adjusting both frequency and duty cycle of the drive signal during the start phase. This dual-parameter adjustment allows the control circuit to prevent current impulses in the resonant tank (protecting power switches) while maintaining a relatively short start duration, resolving the contradiction between reliability and startup time.
Solution Approach 2:
The patent implements feedback control by detecting the current in the resonant tank and using this information to dynamically adjust both frequency and duty cycle of the drive signal. This closed-loop control ensures power switch safety by preventing current impulses while maintaining efficient startup performance.
Data Source
AI summary
This application provides an LLC converter, a control circuit, a soft start method, an apparatus, and a chip, to reduce start duration of the LLC converter and avoid generating a current impulse in a resonant tank. The LLC converter includes a control circuit, and a switch circuit and a resonant tank that are sequentially coupled and connected. The control circuit is configured to: generate a second drive signal based on the current of the resonant tank and a first drive signal, the second drive signal is at a preset level in a time period in which the current is greater than or equal to a current threshold, the second drive signal is used to turn off the power switch in the switch circuit, and the second drive signal is the same as the first drive signal in a time period in which the current is less than the current threshold.