Sense Resistor Short Detection in Switching Power Converters
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Solution Overview
Problem
Conventional flyback switching power converters face challenges in accurately detecting sense resistor short conditions, often resulting in false positives due to low input voltage fluctuations, which can lead to component damage and improper regulation of output voltage.
Innovation Solution
A controller that monitors both the voltage across the power switch and the sense resistor during the maximum on-time period, using finite on-resistance of the power switch transistor to distinguish between sense resistor shorts and low input voltage conditions by comparing voltages against specific peak current thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a maximum on-time timer is used to detect sense resistor shorts, then component damage is prevented, but false positives occur due to low input voltage fluctuations
Solution Approach 1:
The detection function is segmented into two independent monitoring channels: one monitoring the sense resistor voltage (V_Isense) and another monitoring the power switch voltage (V_DS). Each channel operates with its own threshold comparison, allowing the system to cross-validate results and distinguish true faults from false positives caused by low input voltage
Solution Approach 2:
The power switch voltage (V_DS) serves as an intermediary indicator to detect sense resistor shorts. Instead of relying solely on the sense resistor voltage, the system uses V_DS as a secondary measurement that correlates with primary winding current through the power switch's finite on-resistance, providing an alternative detection path that is immune to sense resistor faults
2Ease of operation
If the power switch is maintained on to regulate output voltage, then output regulation is achieved, but excess current may harm the power switch or other components
Solution Approach 1:
The system performs preliminary detection of sense resistor short conditions by monitoring both V_Isense and V_DS during the maximum on-time period before allowing the power switch to remain on. This preliminary check ensures that the power switch is not subjected to harmful excess current by detecting faults in advance
Solution Approach 2:
The system implements feedback by continuously monitoring the power switch voltage (V_DS) and comparing it against a threshold during the maximum on-time period. This feedback mechanism allows the controller to detect sense resistor shorts and adjust the power switch operation accordingly, preventing excess current damage while maintaining proper output regulation
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 approach enables reliable detection of sense resistor shorts, preventing component damage and ensuring accurate operation by differentiating between actual shorts and false positives caused by low input voltage conditions, thus protecting the converter from over-current-induced failures.
Implementation Method 1
The primary winding current (which is the same as the power switch current) is then proportional to the voltage drop of the sense resistor and may be represented by a voltage, V_Isense
Implementation Method 2
the rate of rise of the S1 switch current is directly affected by the rectified input voltage to the converter... the controller monitors the voltage across the power switch transistor during the maximum on-time period and compares this voltage to a second peak current threshold voltage
Data Source
AI summary
Systems, devices, and methods are provided to enable power converters to use two or more sensing elements to reliably detect a short circuit (or soft-short circuit) existing in the power converter and distinguish these conditions from other operating conditions, such as low voltage conditions or normal operating conditions. The disclosed embodiments enable the accurate detection of fault conditions, such as short circuits or soft short conditions, using a number of sensing elements, such as sense resistors and the inherent resistance of switching devices, while preventing the detection of false positives due to other factors such as low input voltage.