Power Transistor Current Sensing via Source Bond Wires
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Solution Overview
Problem
Current methods for detecting overcurrent in power transistors, especially with newer silicon carbide (SiC) and gallium nitride (GaN) technologies, face challenges such as high-voltage critical nodes, limited dynamics, and increased costs, while existing solutions like DESAT detection and SENSE-FET require special layouts and additional components, leading to inefficiencies and safety concerns.
Innovation Solution
A power transistor arrangement that utilizes a differential amplifier and integrator circuit with three measuring bonding wires to determine both through current and gate charge, allowing for dynamic and accurate measurement of gate charge without external shunts, enabling redundant overcurrent protection and efficient safety shutdowns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If DESAT detection is used for overcurrent measurement, then implementation is easy in IGBT systems, but additional suppression time is required and external high-voltage diodes are needed
Solution Approach 1:
The patent extracts the current measurement function from external high-voltage diodes and suppression circuits by utilizing the intrinsic source inductance of the power transistor and source bond wire. The measurement is performed by sensing voltage across the source bond wire during the desaturation event, eliminating the need for external protective components while maintaining ease of implementation.
Solution Approach 2:
The power transistor's own source inductance and source bond wire are utilized as the sensing element for overcurrent detection. The system serves itself by using its inherent parasitic elements (source inductance) as the measurement component, eliminating the need for external high-voltage diodes and suppression circuits required in conventional DESAT detection.
2Measurement precision
If SENSE-FET is used for current measurement, then dynamic range is improved, but special power semiconductor layout is required and costs increase
Solution Approach 1:
The patent makes the source bond wire serve multiple functions: it acts as both the current-carrying conductor and the sensing element for overcurrent detection. By measuring the voltage across the source bond wire during desaturation, the same structural element performs both power transmission and measurement functions, eliminating the need for special SENSE-FET layouts and maintaining cost-effectiveness.
Solution Approach 2:
Instead of using a specialized SENSE-FET structure with separate sensing elements, the patent uses the existing source bond wire as the sensing element. The voltage across this wire is copied and amplified to provide the overcurrent detection signal, achieving the measurement function without requiring special semiconductor layout or additional costly components.
3Speed
If voltage across source inductance is integrated for current sensing, then measurement speed is improved, but measurement signals become very large requiring additional processing
Solution Approach 1:
The patent applies partial integration of the voltage across the source inductance only during the desaturation event rather than continuous integration. The comparator triggers integration when the desaturation condition is detected, and the integration is stopped when the fault is cleared. This partial action approach maintains the fast response of integration while reducing the complexity of handling continuously large measurement signals.
4Ease of manufacture
If gate charge is measured for overcurrent detection, then cost is reduced and speed is improved, but additional shunt resistor is required in current-source-based gate drivers
Solution Approach 1:
The patent extracts the overcurrent detection function from the gate driver circuit by using the source bond wire voltage during desaturation events. This approach removes the need for additional shunt resistors in the gate driver path, as the measurement is performed on the power path rather than the gate control path. The desaturation detection provides the same overcurrent protection function without modifying the gate driver architecture.
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 solution provides precise and dynamic measurement of gate charge and through current, enabling reliable overcurrent detection and safety shutdowns without additional effort or components, suitable for current source-based gate driver circuits, and reduces measurement errors and costs.
Implementation Method 1
a differential amplifier to determine a voltage difference between both ends of the source bond wire from the voltages obtained from the measuring bond wires and thereby to determine the through-current through the power transistor
Implementation Method 2
a first voltage path of the first bond measuring wire between the first end of the source bond wire and the current sensing circuit, and a second voltage path of the second bond measuring wire between the second end of the source bond wire and the current sensing circuit, are connected via an integrator
Data Source
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AI summary
A description is given of a power transistor arrangement (11) comprising a power transistor (12) and a current measuring circuit (13) which is connected to the power transistor (12) and is intended to determine a through-current through the power transistor (12). The through-current is guided from the source connection (14) of the power transistor (12) via at least one source bonding wire (15). A first measuring bonding wire (16) is connected between a first end (17) of the source bonding wire (15) facing the source connection (14) and the source connection (14). A second measuring bonding wire (18) is connected downstream of a second end (19) of the source bonding wire (15) facing away from the source connection (14). Both measuring bonding wires (16, 18) are connected to the current measuring circuit (13). Known power transistor arrangements have only limited reliable overcurrent protection. According to the invention, in addition to the first and second measuring bonding wires (16, 18), a third measuring bonding wire (21) is connected downstream of the second end (19) of the source bonding wire (15), wherein the third measuring bonding wire (21) is also connected to the current measuring circuit (13). As a result, the gate charge can be determined independently of the current through the source bonding wire (15), thus improving the overcurrent protection for the power transistor (12).