Auto-Calibrating Current Shunt for Power Supply OCP
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Solution Overview
Problem
Conventional AC adapters struggle to meet the UL 60950-1 Standard for Safety's Limited Power Source (LPS) requirements due to high electronic component tolerances, leading to inaccurate overcurrent protection (OCP) and the need for undersizing power supplies to compensate, which affects performance and backward compatibility.
Innovation Solution
Implementing automatic and programmable OCP point calibration and current sense resistor verification in power supplies, allowing for precise OCP settings and compliance with LPS standards without downsizing, using secondary-side auto-calibration techniques and programmable integrated circuits to manage output power and voltage levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional OCP circuits with standard electronic components are used, then the design is simple and cost-effective, but the OCP point accuracy is poor due to component tolerance deviation
Solution Approach 1:
The patent applies preliminary action by performing auto-calibration of the OCP point before normal operation. The system automatically measures the actual trip point of the OCP circuit and stores calibration data in a lookup table, compensating for component tolerances in advance. This allows the system to achieve high OCP accuracy without requiring complex real-time correction circuits during operation.
Solution Approach 2:
The patent implements feedback by using the measured OCP trip point information to adjust and correct the OCP setting. The system monitors the actual trip point through calibration measurements and uses this feedback to compensate for component variations, thereby improving OCP accuracy while maintaining relatively simple circuitry.
2Reliability
If adapter power is undersized to cover electronic component tolerance deviation, then LPS compliance is achieved, but adapter capability is penalized and backward compatibility is impacted
Solution Approach 1:
The patent uses preliminary auto-calibration to determine the actual OCP trip point of each adapter unit before it enters service. By measuring and storing the specific trip point characteristics in a lookup table, the system can confidently operate at the adapter's true maximum power capacity rather than using conservative undersized ratings, thereby maintaining LPS compliance while maximizing power capability.
Solution Approach 2:
The patent changes the parameter approach from fixed conservative power ratings to dynamic, measured trip point values. By implementing auto-calibration that measures actual component tolerances and adjusts the OCP setting accordingly, the system transforms the power capability parameter from a static conservative estimate to a precise measured value, enabling full power utilization while maintaining safety compliance.
3Adaptability or versatility
If Type C adapters support multiple output voltage levels, then versatility is improved, but the OCP circuit must comprehend negotiated power contracts and set corresponding trip points, increasing complexity
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing optimal OCP trip points for different voltage levels and power contracts in a lookup table during auto-calibration. When the adapter negotiates a power contract with a Type C device, it quickly retrieves the appropriate trip point from the pre-computed table rather than performing complex real-time calculations, thereby supporting multiple voltage levels with minimal control complexity.
Solution Approach 2:
The patent introduces an intermediary lookup table that mediates between the complex power contract negotiations and the simple OCP control. The lookup table stores pre-computed trip point values for various voltage and power combinations, acting as an intermediary that translates complex power management requirements into simple, direct OCP settings without requiring complex real-time computation.
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
This solution ensures LPS standard compliance, reduces fabrication costs, and enhances power supply reliability by identifying faulty current sense resistors, enabling true 90 Watt power output without exceeding safety limits, and supporting multiple output voltage levels.
Implementation Method 1
the current shunt having a resistance value selected to yield an expected test current value through the current shunt and the DC current loop
Data Source
AI summary
Systems and methods are provided that may be implemented to provide a power supply with automatic overcurrent protection (OCP) point calibration and/or current sense resistor (Rsense) verification. The provided systems and methods may implement auto-calibration techniques on the secondary side of a power supply to achieve a more precise OCP point than is possible with conventional adapter technology, and in one example may implement auto trimming for OCP voltage threshold value.