Pass Transistor Short Detection Using Sense Current Sampling
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Solution Overview
Problem
Existing circuit protection devices, such as fuses and active circuit protection systems, face challenges in accurately detecting faults in pass transistors, particularly external shorts and transistor failures, which can lead to increased system size and maintenance costs.
Innovation Solution
A short detection circuit is introduced, comprising a pass transistor, a sense transistor, a switched current source, a switched capacitor circuit, and a comparator. This circuit detects internal or external shorts across the pass transistor by comparing the sense current with a threshold value, using a switched capacitor circuit to generate a voltage representative of the sense current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If traditional fuses are used for circuit protection, then over-current protection is provided, but response time is slow (milliseconds to seconds) and precise overcurrent level prediction is difficult
Solution Approach 1:
The patent replaces the mechanical fuse system with an active electronic protection circuit that uses a sense transistor, switched capacitor circuit, and comparator to electronically detect and respond to overcurrent conditions, achieving faster response times and precise current level measurement
Solution Approach 2:
The sense transistor acts as an intermediary element that mirrors the load current and allows precise measurement of current flow through the pass transistor, enabling accurate overcurrent detection without directly interrupting the main current path
2Reliability
If fuses are used for protection, then circuit isolation is achieved, but system downtime increases due to physical replacement requirements
Solution Approach 1:
The active protection circuit continuously monitors current conditions and automatically responds to faults without requiring external intervention or physical replacement, enabling resettable protection that eliminates system downtime associated with fuse replacement
Solution Approach 2:
The circuit uses feedback through the sense transistor and comparator to continuously monitor current levels and automatically adjust or interrupt current flow when fault conditions are detected, providing continuous protection without manual intervention
3Measurement precision
If active circuit protection devices are used, then faster response and accurate fault detection are achieved, but device complexity increases
Solution Approach 1:
The protection function is segmented into distinct modular components: a sense transistor for current sensing, a switched capacitor circuit for signal processing, and a comparator for threshold comparison, making the complex function manageable and implementable
Solution Approach 2:
The sense transistor serves multiple functions including current sensing, signal amplification, and fault detection, reducing the need for separate dedicated components and thereby reducing overall circuit complexity despite the advanced protection capabilities
4Productivity
If pass transistor shorts are not detected, then system operation continues, but damage occurs and maintenance costs increase
Solution Approach 1:
The circuit performs preliminary detection of short conditions through the sense transistor and comparator before significant damage can occur, enabling preventive action to be taken while the system is still operational and preventing catastrophic failure
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
The short detection circuit effectively identifies shorts across the pass transistor, allowing for timely intervention to prevent damage, thereby reducing system downtime and maintenance costs while maintaining accurate fault detection.
Implementation Method 1
The switched capacitor circuit is coupled between the current output and the ground terminal. The comparator has a comparator output, a first comparator input, and a second comparator input. The first comparator input is coupled to the switched capacitor circuit.
Implementation Method 2
The comparator is configured to compare the short detection voltage to a short threshold voltage.
Data Source
AI summary
A short detection circuit includes a first transistor, a switched load circuit, a second transistor, a switched capacitor circuit, and a comparator. The first transistor is configured to conduct a load current. The switched load circuit is coupled to the first transistor. The switched load circuit is configured to switchably draw a test current. The second transistor is coupled to the first transistor. The second transistor is configured to conduct a sense current. The sense current includes first and second portions that are respectively representative of the load current and the test current. The switched capacitor circuit is coupled to the second transistor. The switched capacitor circuit is configured to generate a short detection voltage representative of the second portion. The comparator has a first comparator input coupled to the switched capacitor circuit. The comparator is configured to compare the short detection voltage to a short threshold voltage.