Bi-directional BJT for AC Switching and Low Voltage Drop
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Solution Overview
Problem
Traditional semiconductor power switches face limitations in switching AC power, including lack of AC switching ability, high material costs, complex processing steps, inherent voltage drop, and inability to turn off, which restricts efficiency and implementation of features like short-circuit protection.
Innovation Solution
A bi-directional bipolar junction transistor (BJT) structure with a lightly doped base region and heavily doped collector/emitter regions, allowing for AC switching with low voltage drop and simple drive requirements, enabling efficient mains voltage switching and short-circuit protection without specialized cooling or heatsinks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional semiconductor power switches (BJT, MOSFET, IGBT) are used, then DC voltage switching is achieved, but AC switching ability is lacking
Solution Approach 1:
The device is segmented into symmetrical halves with two collector-emitter regions (C1E1 and C2E2) that can independently handle current in opposite directions. This segmentation allows the single device to function as both an NPN and PNP transistor, providing AC switching capability without requiring separate devices for each polarity.
Solution Approach 2:
The patent creates a universal power transistor that can handle both positive and negative voltage polarities using a single device structure. The symmetrical design with interchangeable collector-emitter pairs allows the same physical device to operate in both NPN and PNP modes, eliminating the need for separate switches for AC applications.
2Reliability
If conventional high voltage BJT structures are used, then voltage handling capability is achieved, but turn-off ability is lost due to latch-up
Solution Approach 1:
The patent implements dynamic control by allowing the device to switch between different operational modes (NPN or PNP dominance) depending on the applied base currents. The symmetrical structure enables flexible control where either collector-emitter pair can be actively managed, preventing latch-up through proper biasing sequences without requiring complex control circuits.
3Loss of energy
If standard power transistor structures are used, then current handling is achieved, but voltage drop at turn on is high (0.8 to 2.5 volts)
Solution Approach 1:
The patent applies local quality optimization by creating heavily doped collector-emitter regions specifically at the current entry and exit points. This localized heavy doping reduces the contact resistance and series resistance in the high-current paths, thereby reducing the voltage drop during conduction without requiring changes to the entire device structure.
4Reliability
If expensive semiconductor materials (such as SiC) are used, then high voltage capability is improved, but material cost increases
Solution Approach 1:
The patent achieves high voltage capability through parameter optimization of standard silicon material rather than switching to expensive SiC. The symmetrical structure with carefully controlled doping profiles and geometric dimensions allows the device to handle high voltages in both polarities using cost-effective silicon, eliminating the need for expensive wide-bandgap materials.
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 bi-directional BJT structure facilitates efficient AC switching with low voltage drop and high voltage handling, enabling smart-power systems to perform diagnostics and data logging without complex cooling systems, while reducing material costs and processing complexity.
Implementation Method 1
During the off-state of the device, the drift region is substantially fully depleted
Implementation Method 2
when a negative voltage is applied to said second CE region, a positive voltage being applied to the base connection and no voltage is applied to the first CE region, the structure is in an on-state in which holes from the second CE region flow through the base region towards the first CE region
Implementation Method 3
a base region of a first conductivity type, wherein said base region constitutes a drift region of said structure; first and second collector/emitter (CE) regions, each of a second conductivity type adjacent opposite ends of said base region
Data Source
AI summary
We disclose a bi-directional bipolar junction transistor (BJT) structure, comprising: a base region of a first conductivity type, wherein said base region constitutes a drift region of said structure; first and second collector/emitter (CE) regions, each of a second conductivity type adjacent opposite ends of said base region; wherein said base region is lightly doped relative to said collector/emitter regions; the structure further comprising: a base connection to said base region, wherein said base connection is within or adjacent to said first collector/emitter region.