Parallel Transistor Circuit With Coupled Kelvin Sources for Current Balancing
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Solution Overview
Problem
Solid state power electronics face challenges in current balancing due to significant differences in threshold voltages between parallel transistors, leading to inefficient switching current and power distribution in high-current, high-voltage applications.
Innovation Solution
A power circuit design with inductively coupled kelvin source connections and source inductors is implemented to balance current distribution between parallel transistors, using specific inductance values and magnetic coupling to minimize differences in threshold voltages and improve current balancing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If parallel transistors are used to handle high current, then current carrying capacity is improved, but current balancing between transistors deteriorates due to threshold voltage differences
Solution Approach 1:
The patent introduces source inductors with specific inductance values to change the electrical parameters of the circuit. By adding inductive reactance in series with each transistor source, the patent modifies the current characteristics to achieve better balancing. The inductors create a frequency-dependent impedance that compensates for threshold voltage differences, allowing parallel transistors to share current more evenly during switching operations.
Solution Approach 2:
The patent uses inductively coupled kelvin source connections as an intermediary mechanism between the parallel transistors. The coupled inductors create a magnetic coupling that provides feedback and interaction between the transistor branches, helping to equalize current distribution. This intermediary coupling allows the system to self-regulate current sharing without requiring precise matching of transistor parameters.
2Device complexity
If conventional parallel transistor configuration is used, then device complexity is reduced, but switching current distribution becomes unbalanced
Solution Approach 1:
The patent modifies the conventional parallel configuration by adding source inductors with optimized inductance values. This parameter change introduces controlled impedance that improves current distribution during the critical switching transient period. The inductors are sized to provide sufficient reactance to balance current without excessively increasing voltage drops or power losses.
Solution Approach 2:
The inductive coupling between kelvin source connections creates a mechanism that tends to equalize the voltage conditions at the sources of parallel transistors. By coupling the inductors magnetically, the patent creates an equipotential-like effect during switching, where the magnetic coupling ensures that voltage transients are distributed more evenly across parallel devices, improving reliability.
3Adaptability or versatility
If transistors with different threshold voltages are used, then device adaptability is improved, but current balancing capability deteriorates
Solution Approach 1:
The patent employs source inductors that introduce frequency-dependent impedance to compensate for threshold voltage variations. By carefully selecting inductance values, the patent creates a circuit where the inductive reactance dominates during switching transients, effectively masking threshold voltage differences. This allows the use of transistors with varying threshold voltages while maintaining good current balancing.
Solution Approach 2:
The patent applies preliminary anti-action by introducing inductors that counteract the harmful effect of threshold voltage differences before they can cause significant current imbalance. The inductive reactance is designed to be sufficient at switching frequencies to preemptively balance the current distribution, preventing the threshold voltage variations from causing problematic imbalance during the critical turn-on and turn-off periods.
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 design enhances the balance of switching current and power between parallel transistors, reducing the need for pre-selection based on threshold voltage matching and improving overall performance in high-power applications.
Implementation Method 1
The kelvin source connections of the two driving transistors are inductively coupled
Data Source
AI summary
A power circuit includes a power source for providing electrical power and two driving transistors being disposed in parallel and receiving electrical power from the power source. Each of the two driving transistors includes a gate terminal, a source connection, and a kelvin source connection. The power circuit also includes a control voltage source having a first terminal and a second terminal. The control voltage source provides a control signal to the two driving transistors for determining driving currents through the two driving transistors. The first terminal is connected to the gate terminals of the two driving transistors, and the second terminal is connected to the kelvin source connections of the two driving transistors. The kelvin source connections of the two driving transistors are inductively coupled.