Overcurrent Protection Circuit with Drain Voltage Correction
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Solution Overview
Problem
Conventional overcurrent protection circuits face reduced detection accuracy due to differences in drain voltages between output and sense transistors, especially when the output terminal is grounded, affecting the ratio of output and sense currents and leading to inaccurate overcurrent detection.
Innovation Solution
An overcurrent protection circuit is designed with a sense transistor, a sense resistor, a current limiting circuit, and a current correction circuit that adjusts the sense current based on the voltage difference between the output and sense transistors' drain voltages, maintaining a constant ratio of output and sense currents regardless of the output terminal voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional overcurrent protection circuit is used without voltage coincidence control, then the circuit operation is simple, but the detection accuracy of overcurrent is reduced due to channel length modulation effect
Solution Approach 1:
The patent dynamically adjusts the drain voltage of the sense transistor to match the drain voltage of the output transistor, compensating for voltage differences that cause channel length modulation effects. This voltage parameter adjustment ensures accurate overcurrent detection across varying output conditions including grounded terminals
Solution Approach 2:
The patent replaces voltage coincidence control mechanisms with a current correction approach using correction transistors that directly compensate for current ratio deviations caused by voltage differences, eliminating the need for complex voltage matching circuits
2Measurement precision
If voltage coincidence control is implemented to maintain accurate detection, then overcurrent detection accuracy is improved, but the device complexity increases
Solution Approach 1:
The patent introduces correction transistors as intermediary elements that mediate between the sense transistor and the sensing circuit, compensating for current ratio deviations without requiring direct voltage coincidence control between the output and sense transistors
Solution Approach 2:
The patent segments the current sensing function into multiple parallel paths: the original sense transistor path and correction transistor paths, allowing independent optimization of each path and simplifying the overall control mechanism
3Reliability
If the output terminal is grounded, then the circuit can handle short-circuit conditions, but the drain voltage difference between output and sense transistors increases causing detection inaccuracy
Solution Approach 1:
The patent applies preliminary correction by introducing correction transistors that pre-compensate for the current ratio deviation caused by drain voltage differences, preventing detection inaccuracy before it occurs during grounded output conditions
Solution Approach 2:
The patent implements feedback mechanisms where the sensing circuit monitors the current through correction transistors and adjusts the correction amount based on the actual voltage difference between output and sense transistors, maintaining accurate detection under varying output conditions
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 configuration ensures high detection accuracy of overcurrents even when the output terminal is grounded, effectively mitigating the channel length modulation effect and maintaining consistent current limiting across varying output voltages.
Implementation Method 1
a sense transistor 13 through which a sense current Is1 proportional to the output current IOUT flows
Implementation Method 2
a sense resistor 14 through which the sense current Is1 flows... a current limiting circuit 30 that detects a sense voltage Vs generated in the sense resistor 14
Implementation Method 3
a ratio between the output current and the sense current may change due to influence of a channel length modulation effect
Data Source
AI summary
An overcurrent protection circuit configured to limit an output current flowing through an output transistor includes a sense transistor that provides a sense current proportional to the output current, a sense resistor through which the sense current flows, a current limiting circuit that detects a sense voltage generated by the sense resistor and controls a gate voltage of the output transistor, and a current correction circuit that provides the sense resistor with a corrected sense current added to the sense current based on a difference of voltage between a drain voltage of the output transistor and a drain voltage of the sense transistor.