Kelvin Feedback Switching for Power Transistor Overcurrent Protection
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Solution Overview
Problem
Power transistors, such as MOSFETs and IGBTs, lack effective overcurrent protection mechanisms that do not compromise their current carrying capacity or switching speed, especially when using wide bandgap semiconductor materials where increasing the semiconductor die area is undesirable.
Innovation Solution
Incorporating a feedback switching element and switching control circuitry that couples and isolates a Kelvin connection node relative to a power switching node based on the transistor's operational mode, providing an inherent feedback mechanism to protect against overcurrent events without affecting switching speed, and using sense resistors and overcurrent protection switching elements to detect and manage overcurrents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If overcurrent protection circuitry is integrated into the semiconductor die of the power transistor, then the overcurrent withstand time is increased, but the current carrying capacity is reduced due to less active area
Solution Approach 1:
A feedback switching element is introduced as an intermediary component coupled between the Kelvin connection node and the second power switching node. This switching element acts as a mediator that provides overcurrent protection by controlling the feedback path without occupying active area on the semiconductor die, thus preserving the current carrying capacity while extending overcurrent withstand time
Solution Approach 2:
The overcurrent protection mechanism is implemented by adding a feedback dimension to the control circuitry rather than expanding the power handling area. The feedback switching element creates a new control dimension that monitors and responds to overcurrent conditions without consuming the active area required for current carrying
2Reliability
If the total area of the semiconductor die is increased to maintain current carrying capacity with protection circuitry, then the overcurrent protection is improved, but the cost increases due to valuable wide bandgap semiconductor material
Solution Approach 1:
The feedback switching element serves as an intermediary that enables overcurrent protection functionality without requiring additional valuable wide bandgap semiconductor material. By placing this element outside the active area or using it to control existing structures, the solution achieves improved reliability without increasing material consumption
3Measurement precision
If resistive elements tolerant of extremely high voltages and currents are used for overcurrent detection, then the detection accuracy is improved, but the device complexity and cost increase
Solution Approach 1:
The feedback switching element acts as an intermediary that transforms the high-voltage, high-current power circuit into a lower-voltage control circuit. By switching the Kelvin connection node based on overcurrent conditions, it enables accurate overcurrent detection using standard sense resistors rather than requiring specialized high-power resistive elements
Solution Approach 2:
The solution replaces the need for mechanically robust high-power resistive elements with an electronic switching mechanism. The feedback switching element electronically controls the detection path, substituting the need for physically robust passive components with an active electronic control approach
Data Source
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AI summary
Support circuitry for a power transistor includes a feedback switching element and switching control circuitry. The feedback switching element is coupled between a Kelvin connection node and a second power switching node. The switching control circuitry is configured to cause the feedback switching element to couple the Kelvin connection node to the second power switching node after the power transistor is switched from a blocking mode of operation to a conduction mode of operation and cause the feedback switching element to isolate the Kelvin connection node from the second power switching node before the power transistor is switched from the conduction mode of operation to the blocking mode of operation.