Stacked Power Transistor Circuit for High-Voltage Switching
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Solution Overview
Problem
Conventional power Field Effect Transistors (FETs) are unable to withstand very high voltages between their drain and source terminals, limiting their application in high-voltage circuit scenarios.
Innovation Solution
A High-Voltage Stacked Transistor Circuit (HVSTC) is developed, comprising a stack of power transistors coupled in series with associated bipolar transistors, allowing all transistors to turn on or off simultaneously, effectively increasing the breakdown voltage between terminals beyond that of individual transistors, and utilizing a control input signal to manage the static on or off states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If multiple power FETs are connected in a stacked configuration to withstand high voltage, then the overall breakdown voltage is increased, but the circuit complexity increases due to the need for additional control mechanisms
Solution Approach 1:
The high-voltage switch is segmented into multiple power FETs connected in series, where each FET handles a portion of the total voltage. This segmentation allows the overall breakdown voltage to be increased beyond what a single FET can withstand, while managing the complexity through systematic control of individual segments.
Solution Approach 2:
The control circuit performs preliminary actions by pre-charging gate-to-source capacitances and coordinating the turn-on sequence of individual FETs before the main switching event. This preliminary preparation ensures that voltage is distributed properly across all FETs during switching, preventing any single device from exceeding its breakdown voltage.
2Speed
If all power FETs in the stack are turned on simultaneously, then the switching speed is improved, but the risk of exceeding individual FET breakdown voltage increases during transient states
Solution Approach 1:
Before simultaneously turning on all FETs, the control circuit performs preliminary charging of gate-to-source capacitances and ensures proper voltage distribution across the stack. This preliminary action prepares each FET to handle the voltage conditions during simultaneous switching, maintaining both speed and reliability.
Solution Approach 2:
The control circuit provides beforehand cushioning by coordinating the turn-on timing and ensuring that voltage stress on any individual FET never exceeds its breakdown voltage, even during the transient switching period. This protective measure allows simultaneous switching without compromising device reliability.
3Strength
If multiple power FETs are used in a stacked configuration, then the voltage handling capability is improved, but the number of components and control circuitry increases
Solution Approach 1:
The voltage handling capability is improved by segmenting the single high-voltage switch into multiple lower-voltage FETs connected in series. Each FET is designed to handle a specific portion of the total voltage, allowing the system to achieve high voltage capability while using standard, readily available components.
Solution Approach 2:
The control circuit is designed with multi-functionality, serving multiple purposes: it controls the turn-on and turn-off sequences of individual FETs, pre-charges gate capacitances, distributes voltage during switching, and protects against breakdown. This universal control approach manages the increased component count through integrated functionality.
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 HVSTC operates as a single high-breakdown-voltage transistor, enabling the handling of high voltages exceeding 6500 volts, while ensuring no individual transistor exceeds its breakdown voltage during switching, thus enhancing the reliability and efficiency of high-voltage circuit operations.
Implementation Method 1
The bipolar transistors are conductive (in one example in the reverse active mode) in such a way that they keep their associated power transistors off
Data Source
AI summary
A High-Voltage Stacked Transistor Circuit (HVSTC) includes a stack of power transistors coupled in series between a first terminal and a second terminal. The HVSTC also has a control terminal for turning on an off the power transistors of the stack. All of the power transistors of the stack turn on together, and turn off together, so that the overall stack operates like a single transistor having a higher breakdown voltage. Each power transistor, other than the one most directly coupled to the first terminal, has an associated bipolar transistor. In a static on state of the HVSTC, the bipolar transistors are off. The associated power transistors can therefore be turned on. In a static off state of the HVSTC, the bipolar transistors are conductive (in one example, in the reverse active mode) in such a way that they keep their associated power transistors off.