Output Transistor Fail-Safe Circuit for Supply Line Disconnection
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Solution Overview
Problem
Semiconductor devices face issues with abnormal current occurrence due to disconnection of power supply or ground lines, as existing detection circuits fail to detect these disconnections and do not provide adequate fail-safe functions.
Innovation Solution
A semiconductor device design that includes power supply terminals, an output terminal, output transistors, a disconnection detection circuit, and an output transistor control circuit, which detects disconnections in power supply or ground lines and controls the output transistors to prevent abnormal current by turning off the switch transistors or output transistors, thereby isolating the current path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the back gate terminal of the output transistor is connected to the power supply line or ground line, then the transistor can be controlled to drive voltage at the output terminal, but abnormal current occurs when power supply or ground line is disconnected due to body diode conduction
Solution Approach 1:
A disconnection detection circuit is introduced as an intermediary between the power supply/ground lines and the output transistor control. This circuit detects disconnection conditions and generates control signals to prevent abnormal current by turning off the output transistor when disconnection is detected, thus mediating the harmful effect before it can occur.
Solution Approach 2:
The disconnection detection circuit performs preliminary detection of power supply or ground line disconnection before abnormal current can flow through the body diode. By detecting the disconnection condition in advance and preemptively turning off the output transistor, the system prevents the harmful effect rather than reacting to it after occurrence.
2Reliability
If a detection circuit is added to detect power supply or ground line disconnection, then fail-safe function is improved, but device complexity increases
Solution Approach 1:
The disconnection detection circuit is designed to detect both power supply line disconnection and ground line disconnection using a unified detection mechanism. The same detection circuit generates control signals for both the first output transistor (connected to power supply) and the second output transistor (connected to ground), achieving multi-functionality with a single circuit block.
3Object-affected harmful factors
If the output transistor is turned off to prevent abnormal current, then safety is improved, but normal output function is lost
Solution Approach 1:
The output transistor operates dynamically, switching between on and off states based on real-time detection of disconnection conditions. During normal operation, the transistor remains on to enable output function. When disconnection is detected, the transistor turns off to prevent abnormal current. This dynamic control ensures the transistor adapts to changing conditions rather than being statically fixed.
Solution Approach 2:
The disconnection detection circuit provides feedback about the power supply and ground line status to the output transistor control. This feedback mechanism allows the system to continuously monitor conditions and adjust the transistor state accordingly - maintaining normal operation when conditions are good and preventing abnormal current when disconnection occurs.
Data Source
AI summary
First and second output transistors are connected in series between a power supply terminal and a ground terminal through an output node connected to an output terminal. An output transistor control circuit is arranged corresponding to at least one of the first and second output transistors and is configured to input a voltage at the output terminal to the gate of the first output transistor at a time of occurrence of disconnection of the power supply terminal and input the same to the gate of the second output transistor at a time of occurrence of disconnection of the ground terminal. The first output transistor has a conductivity type to turn off when a power supply voltage is input to the gate, and the second output transistor has a conductivity type to turn off when a ground voltage is input to the gate.