Transistor Short-Circuit Detection Using Surface Temperature Estimation
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Solution Overview
Problem
Conventional overcurrent detection circuitry in transistors is ineffective during transient conditions, leading to potential damage from short circuits due to blanking time issues, either causing damage if too long or false alarms if too short.
Innovation Solution
A short-circuit detection circuit that estimates the surface temperature of transistors using a resistor-capacitor ladder circuit to model semiconductor material, converting current to a scaled current and comparing it against a temperature threshold to accurately detect short circuits during transistor switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional overcurrent detection circuitry is used to detect short circuits, then detection capability is provided, but detection accuracy during transistor switching deteriorates due to transient issues
Solution Approach 1:
The patent introduces a sense transistor as an intermediary device that replicates the switching transistor's behavior. The sense transistor operates in parallel with the switching transistor and experiences the same gate voltage and current conditions. By monitoring the sense transistor's source voltage through a sense resistor, the circuit can detect short circuit conditions without being directly exposed to the high-current transients affecting the main switching transistor. This intermediary approach isolates the detection circuit from harmful transients while maintaining accurate detection capability.
Solution Approach 2:
The sense transistor serves as a scaled-down copy or model of the switching transistor. It replicates the electrical characteristics and switching behavior of the main transistor but operates at lower current levels. The sense transistor's drain current is proportional to the switching transistor's drain current, allowing the detection circuit to observe and analyze transistor behavior under controlled conditions. This copying mechanism enables accurate detection of short circuit conditions without exposing the detection circuit to the full stress of main transistor operation.
2Reliability
If detection sensitivity is increased to detect short circuits early, then protection capability is improved, but false detection increases due to switching transients
Solution Approach 1:
The sense transistor is configured to operate simultaneously with the switching transistor, experiencing the same gate voltage and current conditions from the outset. This preliminary action allows the detection circuit to monitor transistor behavior in real-time from the moment switching begins, enabling early detection of short circuit conditions before they cause damage. The sense transistor's proportional current relationship with the switching transistor ensures that short circuit conditions are reflected in the sense transistor's operation, allowing proactive protection measures.
3Measurement precision
If blanking time is extended to avoid false detection during switching, then false detection is reduced, but detection response time increases potentially allowing damage
Solution Approach 1:
The patent replaces the conventional approach of using time-based blanking mechanisms with a voltage-based detection mechanism. Instead of disabling detection during switching transients through time delays, the circuit continuously monitors the sense transistor's source voltage. The detection circuit responds to voltage thresholds that indicate short circuit conditions, independent of the switching timing. This substitution of mechanical/time-based control with voltage-based sensing eliminates the trade-off between blanking time and detection speed, enabling immediate response to actual short circuit conditions without false triggering during normal switching.
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
Effectively protects transistors by accurately detecting short circuits during transient conditions, preventing damage by turning off the switching transistor when surface temperature exceeds a predetermined threshold.
Implementation Method 1
The sense resistor includes a first terminal coupled to the current terminal, and a second terminal. The amplifier includes a first input coupled to the first terminal of the sense resistor, and a second input coupled to the second terminal of the sense resistor
Implementation Method 2
The resistor-capacitor ladder is coupled to the amplifier, and is configured to generate a measurement voltage that represents a surface temperature rise due to the current through the current terminal
Data Source
AI summary
A short circuit detection circuit includes a current terminal, a sense resistor, an amplifier, and a resistor-capacitor ladder. The sense resistor is coupled to the current terminal, and is configured to develop a sense voltage proportional to a current through the current terminal. The amplifier is coupled to the sense resistor, and is configured to generate a scaled current proportional to the sense voltage. The resistor-capacitor ladder is coupled to the amplifier, and is configured to generate a measurement voltage that represents a surface temperature rise due to the current through the current terminal.