Power Transistor Avalanche Clamping for Overvoltage Protection
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Solution Overview
Problem
Conventional vehicle on-board electric power systems face inefficiencies and high costs due to the need for high zener clamping voltages to handle load dumping, which leads to increased chip area, higher power losses, and potential thermal damage to power transistors.
Innovation Solution
Implementing a power transistor with a drain-source breakdown voltage and clamping voltage that both have positive temperature coefficients, allowing for inherent avalanche clamping that synchronously rises with temperature, reducing the clamping voltage to below anticipated maximum overvoltages and matching it with the breakdown voltage, thereby reducing semiconductor demand and chip area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high zener clamping voltages are used to handle load dumping, then overvoltage protection is improved, but chip area increases and manufacturing costs rise
Solution Approach 1:
The patent changes the temperature coefficient parameter of the clamping voltage from negative (conventional zener diodes) to positive, enabling the clamping voltage to rise synchronously with the breakdown voltage of the power transistor. This parameter change allows the clamping voltage to be reduced to below the maximum anticipated overvoltage while maintaining effective protection, thereby reducing chip area and manufacturing costs
Solution Approach 2:
The power transistor's own breakdown voltage characteristic (with positive temperature coefficient) is utilized to provide the clamping function. The inherent avalanche breakdown of the power transistor works in conjunction with the clamping diode, making the system self-regulating and eliminating the need for separate high-voltage zener diodes, thus reducing chip area
2Reliability
If high zener clamping voltages are used to handle load dumping, then overvoltage protection is improved, but manufacturing costs increase
Solution Approach 1:
By changing the temperature coefficient parameter to positive, the clamping voltage can be set lower than the maximum overvoltage while still providing effective protection. This reduces the voltage rating requirements for semiconductor components, lowering manufacturing costs
Solution Approach 2:
The patent extracts the clamping function from separate high-voltage zener diodes and integrates it with the power transistor's inherent breakdown characteristics. This eliminates the need for expensive high-voltage rated discrete components and simplifies the manufacturing process
3Reliability
If high zener clamping voltages are used to handle load dumping, then overvoltage protection is improved, but thermal loading and power losses increase
Solution Approach 1:
The positive temperature coefficient of the clamping voltage causes it to rise with temperature, synchronously with the breakdown voltage. This reduces the voltage differential across the clamping diode during operation, thereby reducing power losses and thermal loading compared to conventional negative temperature coefficient zener diodes
Solution Approach 2:
The patent converts the typically harmful thermal runout effect into a beneficial self-regulating mechanism. The positive temperature coefficient causes the clamping voltage to increase with temperature, automatically reducing current and preventing thermal runaway, thus converting thermal stress into a protective feature that reduces power losses
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 approach significantly reduces the breakdown voltage of power transistors, lowers manufacturing costs, and allows for more compact designs while effectively protecting against overvoltages, reducing thermal loading and power losses.
Implementation Method 1
The power transistor has a drain-source breakdown voltage VDS with a positive temperature coefficient TKDS... The clamping means has a clamping voltage VCLAMP with a positive temperature coefficient TKCLAMP... allowing for inherent avalanche clamping
Data Source
AI summary
A vehicle on-board electric power system is disclosed including at least one field-effect-controlled power transistor which applies a vehicle on-board electric power system supply voltage VBB to a load when actuated by a logic circuit. The power transistor has a drain-source breakdown voltage VDS with a positive temperature coefficient TKDS and is provided with a clamping means for protecting against overvoltages VO occurring in the vehicle on-board electric power system. The clamping means has a clamping voltage VCLAMP with a positive temperature coefficient TKCLAMP≈TKDS, the clamping voltage VCLAMP being lower than or equal to an anticipated maximum overvoltage VOmax in the vehicle on-board electric power system.