Power Transistor Over-Voltage Protection via Integrated Sensing
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Solution Overview
Problem
Power transistors, such as MOSFETs, are prone to permanent damage from over-voltage due to the lack of integral over-voltage protection, with existing solutions like zener diodes and conventional diodes not effectively tracking fabrication process variations.
Innovation Solution
A semiconductor device with a power transistor and a voltage sensing transistor concurrently fabricated on a substrate, where the voltage sensing transistor has a lower characteristic breakdown voltage, determined by its geometric layout, which turns on to protect the power transistor from over-voltage by limiting the applied voltage through a feedback mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a zener diode and conventional diode are used for over-voltage protection, then the power transistor is protected from over-voltage, but the protection mechanism does not track fabrication process variations
Solution Approach 1:
The invention merges the power transistor and voltage sensing transistor into a single integrated device structure. The voltage sensing transistor is formed in the same semiconductor substrate as the power transistor, with their sources connected together. This integration ensures that both transistors experience the same fabrication process variations, allowing the sensing transistor to accurately track and reflect the actual breakdown voltage of the power transistor.
Solution Approach 2:
The voltage sensing transistor serves itself and the power transistor by automatically sensing the voltage across the power transistor's drain-source terminals and providing feedback to the gate. When the sensed voltage approaches the breakdown voltage, the sensing transistor turns on and reduces the gate voltage, thereby protecting the power transistor without requiring external protection circuits or components.
2Reliability
If external protection circuits are used, then over-voltage protection is provided, but the device complexity increases
Solution Approach 1:
The invention combines the protection function with the power transistor itself by integrating a voltage sensing transistor within the same device structure. This eliminates the need for external zener diodes, conventional diodes, and associated protection circuits shown in FIG. 1, thereby reducing overall device complexity while maintaining reliable over-voltage protection.
Solution Approach 2:
The voltage sensing transistor performs multiple functions: it senses the drain-source voltage, compares it against the breakdown voltage threshold, provides feedback to the gate, and activates protection when needed. This multi-functionality is achieved within a single transistor structure, eliminating the need for separate protection components and simplifying the overall device architecture.
3Reliability
If the breakdown voltage is set close to the MOSFET breakdown voltage, then protection is more effective, but the voltage headroom is reduced
Solution Approach 1:
The voltage sensing transistor continuously monitors the drain-source voltage and provides feedback to the gate through its drain current. When Vds approaches the breakdown voltage Vbd, the sensing transistor turns on and reduces the gate voltage Vgs, thereby preventing Vds from exceeding Vbd. This feedback mechanism allows the breakdown voltage to be set very close to the MOSFET's actual breakdown voltage while still maintaining adequate protection margin.
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
The solution provides self-protection against over-voltage by ensuring the power transistor operates within its safe voltage range, even across varying fabrication processes, enhancing reliability and switching capability.
Implementation Method 1
When the voltage across the first circuit cell first and second terminals reaches the characteristic second element breakdown voltage, the voltage sensing transistor turns on
Data Source
AI summary
In accordance with the principles of the invention, a semiconductor substrate is provided that has a first cell formed thereon. The first cell has first and second terminals or nodes and a control terminal or node and has a characteristic breakdown voltage across the first and second terminals. A voltage sensing transistor is coupled across the power transistor first and second terminals. The voltage sensing transistor has a second element characteristic breakdown voltage that is less than the first cell characteristic breakdown voltage. The voltage sensing transistor provides a control signal to the terminal when the voltage across the first and second terminals exceeds the second element characteristic breakdown voltage.