Transistor Short-Circuit Detection Using RC Thermal Modeling
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Solution Overview
Problem
Conventional overcurrent detection circuitry in transistors is ineffective during transient conditions, leading to potential transistor damage from short circuits due to blanking time variations, either causing damage if too long or false detection 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 with a long blanking time, then false detection is reduced, but transistor damage occurs during short circuits
Solution Approach 1:
The patent changes the detection parameter from current magnitude to temperature estimation. By measuring die temperature rise instead of current directly, the system can detect short circuits during transient conditions without being affected by blanking time, resolving the contradiction between fast detection and false detection reduction
Solution Approach 2:
The patent introduces temperature as an intermediary parameter between current and damage detection. The die temperature rise serves as a mediator that reflects both overcurrent conditions and duration, allowing detection during transient periods without requiring long blanking times
2Speed
If conventional overcurrent detection circuitry is used with a short blanking time, then fast detection is achieved, but false detection occurs
Solution Approach 1:
The patent changes the measurement parameter from instantaneous current to accumulated thermal effect (temperature rise). This allows fast detection during transients while avoiding false positives, as temperature naturally integrates the harmful effect over time
Solution Approach 2:
The die temperature itself serves as the detection signal. The semiconductor material's own thermal response provides the detection information, eliminating the need for external sensing components that introduce delays and false detection issues
3Measurement precision
If temperature-based detection is used, then accurate short circuit detection during transients is achieved, but circuit complexity increases
Solution Approach 1:
The patent uses a simplified RC ladder network that copies the thermal response characteristics of the semiconductor die. This electrical model replicates the temperature behavior without requiring actual temperature sensors, reducing complexity while maintaining detection accuracy
Solution Approach 2:
The patent replaces physical temperature measurement (which would require sensors and complex circuitry) with an electrical analog system. The RC ladder circuit electrically models the thermal system, substituting mechanical/thermal measurement with electrical signal processing
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 from short circuits by accurately detecting them during transient conditions, preventing damage by turning off the switching transistor when the estimated surface temperature exceeds a predetermined threshold.
Implementation Method 1
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
Implementation Method 2
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.