Transistor Overload Protection via Dual Current Comparison
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Solution Overview
Problem
Existing methods fail to effectively detect high impedance short circuits in electronic circuits with transistors, as they do not significantly alter the load current, making it difficult to identify and prevent transistor damage.
Innovation Solution
A method involving the determination of first and second measurement signals based on load currents through two transistors connected in series, with a comparison to detect errors, including high impedance short circuits, using current sensors and an evaluation circuit to generate an error signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional current monitoring methods are used, then low impedance short circuits can be detected through significant voltage increase, but high impedance short circuits cannot be detected as the load current remains within permissible range
Solution Approach 1:
The monitoring function is segmented into two independent measurement paths: one monitoring the load current through the transistor, and another monitoring a reference current that bypasses the load. This segmentation allows comparison between expected and actual current values, enabling detection of high impedance short circuits that would otherwise remain undetected.
Solution Approach 2:
A reference current path is introduced as an intermediary element that provides a baseline for comparison. This reference current flows through a parallel path with known characteristics, allowing the system to detect deviations caused by high impedance short circuits in the load without requiring direct measurement of the fault condition.
2Device complexity
If a single transistor is used to control the load, then the circuit structure is simple, but the transistor cannot be protected from overload caused by high impedance short circuits
Solution Approach 1:
The system implements feedback by continuously comparing the actual load current with the reference current. When a high impedance short circuit occurs, the current imbalance triggers a feedback signal that activates the protection mechanism, switching off the transistor to prevent damage. This feedback loop provides automatic protection without requiring complex external monitoring circuits.
3Measurement precision
If monitoring voltage across the transistor is used, then low impedance short circuits cause detectable voltage increase, but high impedance short circuits do not produce sufficient voltage change for detection
Solution Approach 1:
Instead of directly measuring the difficult-to-detect voltage changes across the transistor during high impedance short circuits, the system introduces a reference current path as an intermediary measurement mechanism. This reference path provides a stable baseline that makes current imbalances caused by high impedance faults easily detectable through comparison, avoiding the limitations of direct voltage monitoring.
Data Source
AI summary
A method is described. The method comprises determining a first measurement signal (CS1) which depends on a first load current (I1) through a first transistor (Q1) which is connected in series to a load (Z); determining a second measurement signal (CS2) which depends on a second load current (I2) through a second transistor (Q2) which is connected in series to the load (Z); and comparing the first measurement signal (CS1) and the second measurement signal (CS2), in order to detect the presence of an error.