Schmitt Trigger Switch Circuit with Hysteresis
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Single BJT switches lack hysteresis, making them unstable to noise in input voltage at threshold levels, requiring complex designs or comparators to introduce hysteresis, which increases cost and complexity.
Innovation Solution
Incorporating a PNP BJT switch and specific resistors and a diode to create a Schmitt trigger switch, enhancing turn-on current and introducing hysteresis without the need for additional power supplies or complex comparators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single BJT switch is used, then the circuit is simple and cost-effective, but the switch lacks hysteresis and becomes unstable to noise at threshold levels
Solution Approach 1:
The patent implements feedback by connecting the output of the NPN transistor back to its base through a resistor network. This feedback mechanism creates hysteresis, where the transistor's state depends not only on the current input but also on its previous state, thereby providing noise immunity and stability without requiring complex comparator circuits.
Solution Approach 2:
The patent changes the electrical parameters at the base of the NPN transistor by introducing an additional PNP transistor that modifies the base voltage and current characteristics. This parameter modification creates effective hysteresis behavior, transforming the simple switch into a stable switching circuit with noise immunity while maintaining overall circuit simplicity.
2Reliability
If multiple BJTs or comparator solutions are used to create hysteresis, then switch stability is improved, but the circuit complexity and cost increase
Solution Approach 1:
The patent merges the functions of hysteresis generation and switching control into a single integrated circuit using two transistors (one NPN and one PNP). This combination achieves the stability benefits of complex hysteresis circuits while maintaining relative simplicity by eliminating the need for separate comparator components and additional power supplies.
Solution Approach 2:
The circuit achieves hysteresis through self-service mechanisms where the transistors' own characteristics and interconnections create the necessary feedback and stability. The PNP transistor automatically adjusts the base conditions of the NPN transistor based on output state, providing self-regulating hysteresis without external control circuits.
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 solution provides a simpler, cost-effective switch circuit with hysteresis, stabilizing the switch operation against noise and reducing the risk of toggling on and off, while allowing adjustable threshold voltage and hysteresis range.
Implementation Method 1
A single BJT switch has no hysteresis. An unstable input voltage (e.g. with noise) at or close to the threshold level to the base may cause the switch to turn on and off repeatedly.
Implementation Method 2
said first transistor being an NPN Bipolar Gate Transistor (Q1)... said second transistor being a PNP Bipolar Gate Transistor
Data Source
AI summary
Switch circuitry including an input terminal (1), said input terminal connected to the base of a first transistor (Q1) via a first resistor (R3), said first transistor being an NPN Bipolar Gate Transistor (Q1), said circuitry further comprising a second resistor (R5) connected between the base of said first transistor (Q1) and ground, and including an output line or terminal (3) connected to the collector of said first transistor (Q1), and wherein the emitter of said first transistor (Q1) is connected to ground (earth), said circuitry further including a second transistor (Q2), said second transistor being a PNP Bipolar Gate Transistor, wherein the collector of said second transistor (Q2) is connected via a third resistor (R8) to the base of said first transistor (Q1), and the emitter of said second transistor (Q2) is connected to said input terminal (1), and wherein the emitter of said second transistor (Q2) is additionally connected to the base of said second transistor (Q2) via a fourth resistor (R11); and the base of said second transistor (Q2) being additionally connected to the output terminal (3) via a fifth resistor (R10) and a diode (D1).