H-Bridge Transistor Malfunction Detection via Drain-Source Voltage
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Solution Overview
Problem
Existing methods for detecting excess current in H bridge circuits, such as those used in motor control, fail to accurately identify malfunctions when excess current flows through alternative paths due to transistor breakdown, leading to incomplete detection and potential damage.
Innovation Solution
A circuit device with a malfunction detection circuit that compares the voltage between the drain and source nodes of transistors in an H bridge circuit to a set comparison voltage, allowing for accurate detection of malfunctions by determining if the voltage exceeds the comparison voltage before the completion of a charge period, and includes a control circuit to stop excess current flow when a malfunction is detected.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage detection method using sense resistors is used to detect excess current, then excess current can be detected in normal operation, but excess current caused by transistor breakdown cannot be detected when alternative current paths are generated
Solution Approach 1:
The detection function is segmented into two independent detection mechanisms: (1) sense resistor voltage detection for normal excess current, and (2) transistor drain-source voltage detection for breakdown conditions. This segmentation allows each detection method to specialize in detecting specific failure modes without interfering with the other, resolving the contradiction between detection accuracy and detection completeness.
Solution Approach 2:
The transistor's drain-source voltage serves as an intermediary indicator for detecting breakdown conditions. Instead of directly detecting current paths, the system uses the voltage across the transistor as a mediator to infer the presence of breakdown, enabling detection of alternative current paths that bypass the sense resistors.
2Object-generated harmful factors
If sense resistor voltage increase is used as malfunction indicator, then normal excess current is detected, but breakdown current flowing through substrate cannot be detected
Solution Approach 1:
Instead of detecting current flow directly through sense resistors, the invention inverts the approach by detecting the voltage across the transistor itself. When breakdown occurs, the voltage across the transistor drops or changes in a detectable way, providing an inverse indication of the malfunction that complements the sense resistor method.
Solution Approach 2:
The system continuously monitors transistor drain-source voltage as a preliminary indicator of potential breakdown before it causes damage. This preliminary detection mechanism is always active and ready to detect breakdown conditions before they result in harmful effects, complementing the reactive sense resistor detection.
3Device complexity
If only sense resistor detection is implemented, then circuit complexity is low, but detection coverage is incomplete for all malfunction types
Solution Approach 1:
The invention merges two detection circuits into a unified malfunction detection system: the sense resistor voltage detection circuit and the transistor drain-source voltage detection circuit. Both circuits share common components such as the comparator and control logic, reducing overall complexity while achieving comprehensive detection coverage for both normal excess current and breakdown conditions.
Data Source
AI summary
A circuit device includes an output circuit having a high-side transistor and a low-side transistor, and a control circuit configured to detect a voltage between the drain node and the source node of a detection target transistor that is at least one of the low-side transistor and the high-side transistor, and detect a malfunction in the case where it is determined that the detection voltage did not exceed a given comparison voltage.