LLC Resonant Converter Overcurrent Protection Circuit
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Solution Overview
Problem
Resonant switch mode power supplies, particularly LLC converters, face challenges in detecting overcurrent conditions accurately, especially when operating at lower input voltages, as the primary current may not rise enough to trigger traditional threshold-based detection methods.
Innovation Solution
The implementation of an overcurrent protection circuit that perturbs the current sense signal to generate a perturbed current sense signal, allowing for detection above both high and low thresholds, ensuring accurate overload detection even at reduced input voltages or lower switching frequencies, using a combination of comparators, counters, and logic gates to assert an overcurrent signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional threshold-based overcurrent detection is used, then the detection method is simple, but it fails to detect overcurrent conditions at lower input voltages
Solution Approach 1:
The patent introduces a perturbation signal as an intermediary element that modifies the current sense signal. This perturbation signal, when combined with the original signal through addition, creates a perturbed current sense signal that enhances the detectability of overcurrent conditions at lower input voltages without requiring a complete redesign of the detection mechanism
Solution Approach 2:
The patent changes the parameter of the current sense signal by adding a perturbation component to it. This transforms the original current sense signal into a perturbed current sense signal with modified characteristics that enable reliable overcurrent detection across a wider range of input voltages, including lower voltages where traditional methods fail
2Reliability
If the primary current threshold is increased to detect overcurrent at lower input voltages, then detection sensitivity improves, but false triggering at normal operating conditions increases
Solution Approach 1:
The patent segments the overcurrent detection process into two distinct stages: first, generating a perturbed current sense signal for enhanced sensitivity, and second, comparing this perturbed signal against a threshold to determine overcurrent conditions. This segmentation allows each stage to be optimized independently, preventing false triggering while maintaining detection sensitivity
Solution Approach 2:
The patent employs feedback through the comparison of the perturbed current sense signal with a reference threshold. The output of this comparison feeds into the control logic that determines whether to trigger overcurrent protection, creating a closed-loop detection system that can distinguish between normal variations and actual overcurrent conditions
Data Source
AI summary
An LLC resonant converter controller comprising an overcurrent protection circuit coupled to receive a current sense signal representative of current in a primary winding, wherein the overcurrent protection circuit outputs an overcurrent signal when the perturbed current sense signal is above a low threshold for a number of consecutive switching cycles. The LLC resonant converter controller further includes a control circuit coupled to generate a high side drive signal and a low side drive signal in response to a feedback signal representative of an output of an LLC resonant converter is further coupled to receive the overcurrent signal and is operable to disable switching of the first power switch and second power switch in response to the overcurrent signal.