MOSFET Diode-OR Failure Detection via Superimposed Test Voltage
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Solution Overview
Problem
Existing failure detection devices for switch units, such as MOSFETs, struggle to detect ON failures due to parasitic diodes creating a bypass path, and the inability to freely adjust output voltages in applications like vehicle equipment limits effective detection.
Innovation Solution
A failure detection device is designed with a diode OR configuration using three switch units, each with a parasitic diode, and a failure detection unit that applies a specified voltage to a connection point when all switch units are turned off, allowing for ON failure detection by monitoring the voltage at this point.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If back-to-back MOSFETs are used in a diode OR configuration, then the circuit can operate with reduced switch units, but the parasitic diode creates a bypass path that prevents ON failure detection
Solution Approach 1:
The invention applies a test voltage to the connection point before normal operation to detect ON failures. By proactively applying a voltage higher than the parasitic diode's forward voltage during a test period, the system can detect if MOSFETs are stuck ON by measuring current flow, thus resolving the detection problem while maintaining the simplified diode OR configuration
Solution Approach 2:
The failure detection function is integrated into the normal operation by periodically applying test voltages during idle periods or transition states. This allows continuous monitoring of switch unit health without adding separate detection circuits, maintaining both simplicity and reliability
2Reliability
If output voltage is increased or decreased to create a potential difference for failure detection, then ON failure can be detected, but the voltage cannot be freely adjusted due to equipment operating requirements
Solution Approach 1:
The invention applies a test voltage that temporarily exceeds the normal operating voltage during detection periods. This excessive voltage application is limited to specific test windows when no load is connected, allowing sufficient potential difference for detection without affecting normal equipment operation. The test voltage is applied only partially in time, not continuously
Solution Approach 2:
The failure detection is performed periodically during idle periods or transition states rather than continuously. The system alternates between normal operation mode and test mode, applying detection voltages only during appropriate windows when the diode OR circuit is not supplying load current, thus maintaining adaptability while enabling detection
3Reliability
If a DC/DC converter is added to adjust output voltage for failure detection, then ON failure detection becomes possible, but the system complexity and cost increase
Solution Approach 1:
The existing DC/DC converter is made multi-functional by using it both for normal voltage regulation and for applying test voltages during failure detection. The converter's existing capability to adjust output voltage is leveraged for dual purposes: maintaining normal operation voltage and providing elevated test voltages during detection periods, thus avoiding additional hardware while enabling detection functionality
Solution Approach 2:
The system uses its own existing DC/DC converter to perform the failure detection function without requiring external test equipment or additional voltage sources. The converter serves itself by switching between regulation mode and test voltage application mode, eliminating the need for separate detection hardware and reducing overall system complexity
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
This configuration enables the detection of ON failures while minimizing the number of switch units required, thus reducing complexity and increasing reliability in power supply systems.
Implementation Method 1
a voltage application unit applying a specified voltage to the connection point in a superimposed manner when all of the first switch unit, the second switch unit, and the third switch unit are controlled to be turned off
Implementation Method 2
a first switch unit in which a first terminal is connected to a first battery that outputs a predetermined voltage and a second terminal is connected to a connection point, and that includes a parasitic diode preventing a current from flowing from the second terminal to the first terminal
Implementation Method 3
a voltage detection unit detecting a voltage of the connection point in an application state by the voltage application unit
Implementation Method 4
an ON failure determination unit determining that at least one of the first switch unit and the second switch unit has an ON failure when the voltage detected by the voltage detection unit exceeds the predetermined voltage, and is not greater than or equal to a threshold set to be less than a value obtained by subtracting a voltage drop due to the parasitic diode of the first switch unit and the parasitic diode of the second switch unit after adding the specified voltage to the predetermined voltage
Data Source
AI summary
A failure detection device includes a first, second and third switch units, and a failure detection unit detecting an ON failure of the first switch unit and the second switch unit. The failure detection unit includes a voltage application unit applying a specified voltage to the connection point in a superimposed manner when all of the first, second, and third switch units are controlled to be turned off, a voltage detection unit detecting a voltage of the connection point in an application state by the voltage application unit, and an ON failure determination unit determining that at least one of the first and second switch units has an ON failure when the voltage detected by the voltage detection unit is not greater than or equal to a threshold.