Two-Wire Transmitter Starter Circuit for Stable Startup
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Solution Overview
Problem
Two-wire transmitters with time constant circuits face instability during startup when the external power supply changes slowly, affecting reliable starting and stability.
Innovation Solution
A two-wire transmitter design incorporating a starter circuit with a comparator and switching section, utilizing a pnp transistor to control the flow of current and ensure stable startup independent of external power supply methods, with a comparator comparing output voltage to a reference voltage and switching on/off accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a time constant circuit is used as the starter circuit, then the transmitter can provide stable power supply during startup, but the transmitter becomes unstable when external power supply voltage changes slowly
Solution Approach 1:
The patent replaces the static time constant circuit with a dynamic control circuit that actively responds to voltage changes. The operational amplifier continuously monitors the voltage across capacitor C1 and adjusts the conduction state of transistor Q3 accordingly, enabling the circuit to adapt to different power supply conditions (fast or slow voltage changes) rather than being fixed in its response characteristics.
Solution Approach 2:
The patent introduces a feedback mechanism where the operational amplifier monitors the voltage across capacitor C1 and uses this information to control transistor Q3. This closed-loop feedback system ensures that the starter circuit operates correctly regardless of whether the external power supply voltage changes slowly or rapidly, resolving the adaptability issue while maintaining startup stability.
2Productivity
If a time constant circuit is used, then the startup process is controlled passively, but the control effectiveness is insufficient when power supply voltage changes slowly
Solution Approach 1:
The patent enables the starter circuit to self-regulate its operation based on real-time voltage conditions. The operational amplifier automatically detects when the voltage across capacitor C1 reaches the threshold and switches transistor Q3 off at the appropriate moment, eliminating the need for external adjustment or manual intervention while ensuring reliable startup under all power supply conditions.
Solution Approach 2:
The patent replaces the passive electrical time constant mechanism with an active electronic control system using operational amplifiers and transistors. This substitution transforms the startup control from a purely time-based passive process to an actively controlled process that can reliably detect and respond to voltage changes regardless of their rate, ensuring both startup speed and reliability.
3Device complexity
If the starter circuit uses a simple time constant configuration, then the device complexity is low, but the measurement precision of voltage change detection is insufficient
Solution Approach 1:
The patent replaces the simple time constant circuit with an operational amplifier-based voltage detection system. The operational amplifier provides high-precision voltage comparison and amplification, enabling accurate detection of the voltage across capacitor C1. This electronic substitution significantly improves measurement precision while adding only moderate circuit complexity compared to the simplicity of the original time constant approach.
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 stable start characteristic and ensures reliable power supply during startup, independent of external power supply methods, maintaining stability even when voltage Vcc lowers due to anomalies.
Implementation Method 1
The two-wire transmitter 10' includes the power supply section 40 formed of a Zener diode, for example, and the internal circuit 50 having a sensor (not shown), a microprocessor (not shown), etc. More particularly, an anode of the Zener diode of the power supply section 40 is connected to the common potential COM and a cathode of the Zener diode of the power supply section 40 is connected to the opposite end of the current control circuit 30 (voltage Vcc).
Implementation Method 2
A drain of an n channel depletion type field effect transistor (FET) Q4 is connected to the one end of the current control circuit 30 (transmission line L1) and a source of the FET Q4 is connected to the opposite end of the current control circuit 30. The voltage Vg lowers having the time constant of the resistors R5, R6, and R7 and the capacitor C, the gate-source voltage of the FET Q4 (Vg−Vcc) lowers and becomes equal to or less than the cutoff voltage, and the FET Q4 is turned off.
Implementation Method 3
A series circuit of resistors R5 and R6 is connected between the opposite end of the current control circuit 30 (voltage Vcc) and the common potential COM. Further, a resistor R7 is connected between the connection point of the resistors R5 and R6 and a gate of the FET Q4. A capacitor C is connected between the opposite end of the current control circuit 30 (voltage Vcc) and the gate of the FET Q4. The resistors R5, R6, and R7 and the capacitor C make up a time constant circuit.
Data Source
AI summary
A two-wire transmitter is connected to two transmission lines which transmit an electric signal regarding a physical quantity detected by a sensor. The two-wire transmitter includes a current control section which controls a transmission current of the electric signal, and a starter circuit which starts at a starting time of the two-wire transmitter so that the transmission current flowing through the current control section under steady operation of the two-wire transmitter detours the current control section to flow through the starter circuit. The starter circuit stops when an output voltage of the current control section reaches a predetermined value or more after the two-wire transmitter starts.