LLC Resonant Converter Control for False Over-Current Trips
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Solution Overview
Problem
Dual-output LLC resonant power converters under asymmetric PWM control face challenges in providing effective protections such as over-current protection due to the complexity of managing duty cycles and avoiding false triggering.
Innovation Solution
An LLC controller is implemented to determine load conditions by adjusting thresholds based on duty cycles of high-side and low-side switches, preventing false over-current protection triggering by extending the acceptable range of current-sense signals within defined thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If asymmetric PWM control is used to regulate two output power sources in a dual-output LLC resonant power converter, then the power converter can supply power to two different loads with different conditions, but it becomes difficult to provide effective protections such as over-current protection due to the complexity of managing duty cycles
Solution Approach 1:
The patent applies dynamics by making the over-current protection threshold dynamic rather than fixed. The threshold is adjusted in real-time based on the duty cycle of the primary switch, allowing the protection mechanism to adapt to varying operating conditions in asymmetric PWM mode while maintaining reliability
Solution Approach 2:
The patent changes the parameter of the protection threshold based on the duty cycle. By correlating the over-current threshold with the duty cycle parameter, the system can provide effective protection across different operating points without requiring complex additional control circuits
2Device complexity
If fixed thresholds are used for over-current protection in asymmetric PWM mode, then the protection circuit is simple to implement, but false triggering occurs due to the varying duty cycles of high-side and low-side switches
Solution Approach 1:
The protection threshold is made dynamic by adjusting it according to the duty cycle of the primary switch. This dynamic adjustment prevents false triggering while keeping the circuit relatively simple, as it uses existing duty cycle information rather than requiring entirely new sensing circuits
Solution Approach 2:
The patent uses feedback by monitoring the duty cycle of the primary switch and using this information to adjust the over-current protection threshold. This feedback mechanism ensures the threshold adapts to current operating conditions, preventing false triggering without significantly increasing circuit complexity
Data Source
AI summary
A control method is disclosed to prevent false triggering of over-current protection. A power converter comprises high-side and low-side switches connected in series between an input power line and a ground line, for driving a resonant circuit to resonate. The power converter includes a detector detecting the resonant circuit to provide a detection signal representing a magnitude of resonance in the resonant circuit. A duty cycle of one of the high-side and low-side switches is detected, and a threshold is determined in response to the duty cycle. An over-current protection is triggered based on the threshold and the detection signal. When the over-current protection is triggered, at least one of the high-side and low-side switches stops providing power to the resonant circuit, and the resonance subsides.