Office-Line Trunk Circuit Dual-Mode Detection
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Solution Overview
Problem
Conventional office-line trunk circuits face difficulties in selectively operating in both loop-start and ground-start modes without requiring additional hardware or self-power supplies, which complicates insulation between the primary and secondary sides of an office line.
Innovation Solution
An office-line trunk circuit with a DC current detection circuit and an incoming detection circuit, utilizing a high-resistance photo coupler to detect loop currents and ring signals, respectively, allowing for both loop-start and ground-start operations without a switch circuit or self-power supply on the primary side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a self power supply is used in the ground-start circuit, then the circuit can operate in both loop-start and ground-start modes, but insulation between the primary side (office exchange) and secondary side (PBX) cannot be established
Solution Approach 1:
The patent extracts the power supply function from the PBX side and relocates it entirely to the office exchange side. The high-resistance detection circuit on the PBX side receives power through the telephone line itself rather than having a local power supply, thereby achieving insulation between primary and secondary sides while maintaining dual-mode operation capability
Solution Approach 2:
The patent introduces the telephone line as an intermediary power transmission medium. The high-resistance detection circuit is powered through the office line from the office exchange side, using the line itself as both signal and power carrier, which enables insulation while maintaining functionality
2Adaptability or versatility
If a switch circuit is used to select between loop-start and ground-start modes, then the circuit can be configured for different operations, but the device complexity increases
Solution Approach 1:
The patent designs the high-resistance detection circuit to perform multiple functions: it detects ground potential in ground-start mode and detects loop current in loop-start mode. This universal detection capability eliminates the need for separate detection circuits for each mode, thereby removing the requirement for switch circuits while maintaining adaptability to both operation modes
Solution Approach 2:
Instead of using a switch circuit to select between different detection methods for different modes, the patent inverts the approach by designing a single detection circuit that can operate in both modes simultaneously, with the mode determination being automatic based on circuit conditions rather than manual switching
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
Enables seamless operation in both modes with the same hardware configuration, eliminating the need for a switch circuit and self-power supply, thereby securing easy insulation between the primary and secondary sides of the office line.
Implementation Method 1
a high-resistance detection circuit to detect the ground potential... a first photo coupler detecting a loop current
Implementation Method 2
a second photo coupler detecting a ring signal supplied from the office bilateral trunk
Data Source
AI summary
An office-line trunk circuit is provided to selectively operate on ground-start and loop-start modes. In this circuit, a DC current detection circuit has (i) a first photo coupler detecting a DC loop current caused responsively to supply of the ground to a tip line and a negative power to a ring line from an office bilateral trunk and (ii) a resistor whose resistance is adjusted to prevent a loop start in the office bilateral trunk and allow DC current to be detected. The first photo coupler detects the loop current using the resistor. An incoming detection circuit has a second photo coupler detecting a ring signal coming from the office bilateral trunk. A DC sink circuit has a diode bridge placed between the tip and ring lines and configured to have a DC circuit provided with a transistor controlling the DC loop current so that the office bilateral trunk is allowed to selectively be loop-activated and loop-held.