Symmetric Blocking TVS Circuit Using Bipolar Base Snatch
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Solution Overview
Problem
Conventional bi-directional transient voltage suppressors (TVS) face issues with a floating base, leading to voltage variations and increased leakage currents due to the base being disconnected from a potential terminal, which affects their ability to effectively block transient voltages.
Innovation Solution
A bi-directional symmetrical blocking TVS circuit is designed with the base of a bipolar transistor connected to a common source of two MOS transistors, ensuring the base is tied to a lower potential terminal, either positive or negative, using either lateral or vertical configurations, and manufactured using integrated circuit processes to achieve symmetrical bi-directional clamping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the base of the bipolar transistor is left floating to achieve symmetrical NPN/PNP configuration, then the device can provide bi-directional blocking function, but voltage variations over time (dV/dt) occur and leakage current increases
Solution Approach 1:
The patent introduces an intermediary connection between the base and the lower potential terminal through a resistor. This resistor acts as a mediator that provides a controlled path for base current, stabilizing the base potential without completely eliminating the floating characteristic needed for symmetrical operation. The resistor value is carefully selected to balance between base stabilization and maintaining symmetrical breakdown characteristics.
Solution Approach 2:
The patent changes the electrical parameter of the base by connecting it to a lower potential terminal through a resistor, thereby transforming the base from a completely floating state to a partially controlled state. This parameter change stabilizes the base potential and reduces leakage current while preserving the essential symmetrical blocking function through careful selection of the resistor value.
2Reliability
If the base is connected to a lower potential terminal, then leakage current is reduced and base potential is stabilized, but the symmetrical NPN/PNP configuration with identical breakdown voltage is compromised
Solution Approach 1:
The patent applies local quality by making the base connection asymmetric (to lower potential terminal) only in a localized manner through a high-value resistor, while the rest of the NPN and PNP transistor structures maintain identical symmetrical characteristics. This localized asymmetric connection stabilizes the base without significantly affecting the overall symmetrical breakdown voltage of the device.
Solution Approach 2:
The patent deliberately introduces a controlled asymmetry by connecting the base to the lower potential terminal through a resistor. This asymmetric connection is designed to be minimal (high resistance) so that it provides base stabilization while having negligible impact on the symmetrical breakdown characteristics of the NPN/PNP pair, thus resolving the contradiction between asymmetry and symmetry requirements.
3Device complexity
If conventional PN junction device is used, then the structure is simple, but clamping performance is poor due to lack of minority carriers
Solution Approach 1:
The patent employs a composite structure combining PN junction diodes with bipolar transistors (NPN and PNP). This composite configuration leverages the simplicity of the PN junction for basic protection while utilizing the bipolar transistor's minority carrier injection capability to achieve superior clamping performance. The combination of these two device types creates a hybrid structure that satisfies both structural simplicity and performance requirements.
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 configuration significantly reduces leakage currents and enhances the ability to block transient voltages by maintaining a stable base potential, effectively addressing the limitations of conventional TVS designs.
Implementation Method 1
bipolar transistor base snatch to connect the base to a low potential terminal
Implementation Method 2
A TVS can be implemented with the PN junction device that has a breakdown voltage to allow current conduction when a transient input voltage exceeds the breakdown voltage
Data Source
AI summary
A symmetrical blocking transient voltage suppressing (TVS) circuit for suppressing a transient voltage includes an NPN transistor having a base electrically connected to a common source of two transistors whereby the base is tied to a terminal of a low potential in either a positive or a negative voltage transient. The two transistors are two substantially identical transistors for carrying out a substantially symmetrical bi-directional clamping a transient voltage. These two transistors further include a first and second MOSFET transistors having an electrically interconnected source. The first MOSFET transistor further includes a drain connected to a high potential terminal and a gate connected to the terminal of a low potential and the second MOSFET transistor further includes a drain connected to the terminal of a low potential terminal and a gate connected to the high potential terminal.