Transient Voltage Control for Unearthed Subscriber Line Interface Circuits
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Solution Overview
Problem
Cable telephony line cards, not safety grounded, face delays and increased costs due to needing to meet double insulation requirements for transient voltages exceeding safe levels during ringing, as current standards require abnormal testing for continuous internal voltages above 50-60 volts.
Innovation Solution
A system with a voltage converter, controlled by a processor, generates a high voltage ringing signal that is transient in nature, using a flyback transformer or boost converter to increase the voltage from 12-15 V to 90-95 V only during ringing, ensuring the voltage remains below safe levels when not ringing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a continuous 90-95 V voltage node is provided in the line card circuitry, then the ringing signal voltage can be maintained at approximately 40 V RMS, but the device is subjected to abnormal testing and double insulation requirements due to continuous internal voltages exceeding the predetermined safe level
Solution Approach 1:
The patent applies periodic action by switching the voltage node between high voltage (90-95 V) and low voltage states in synchronization with the ringing signal waveform. The voltage converter actively raises the voltage node to 90-95 V only during specific portions of the ringing cycle when the waveform exceeds the safe level, then returns it to a safe continuous level. This periodic switching ensures the voltage exceeds safe levels only transiently during necessary portions of the ring signal, avoiding continuous exposure that would trigger double insulation requirements while maintaining reliable ringing functionality.
2Power
If the voltage node is raised continuously above the predetermined safe level, then the ringing signal can be provided, but the device requires double insulation and abnormal testing which delays market entry
Solution Approach 1:
The voltage converter implements periodic action by dynamically switching the voltage node between high and low states based on the instantaneous waveform of the ringing signal. The controller monitors the ringing waveform and activates the voltage converter only when the waveform exceeds the predetermined safe level, maintaining high voltage power only during those specific transient moments. This ensures adequate ringing power is delivered when needed while avoiding continuous high voltage exposure that would require time-consuming double insulation testing and certification.
3Adaptability or versatility
If a two prong plug is used for power supply compatibility, then the device can work with different receptacle styles, but the device lacks a safety ground path requiring abnormal testing for certification
Solution Approach 1:
The patent applies parameter changes by dynamically altering the voltage level parameter of the internal circuitry based on operational conditions. During normal operation, the voltage node is maintained below the predetermined safe level (50-60 V). During ringing, the voltage converter temporarily increases the voltage to 90-95 V only when the ringing waveform exceeds the safe level. This dynamic parameter adjustment allows the device to achieve adequate ringing voltage while staying within safety parameters for continuous operation, thereby obtaining certification without requiring a safety ground path or double insulation.
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 approach eliminates the need for double insulation requirements, allowing rapid market entry and reduced testing and design costs for certification, as the transient high voltage during ringing does not violate safety standards.
Implementation Method 1
A voltage converter, such as a flyback transformer or boost converter, increases the voltage from 12-15 V to 90-95 V only during ringing
Data Source
AI summary
A voltage controller increases a DC input voltage in response to a ring instruction received from a processor in a control signal. The increased voltage is converted to an AC ring signal that causes a telephone to ring. The ring signal voltage is generated at a battery high node (“VBH”) and may be routed to a SLIC before being sent to an on-hook telephone.The voltage at VBH is kept low during off-hook and other periods when a ring instruction is not present. Thus, voltages internal to an indoor device that houses the controller are kept below a predetermined safe threshold, thereby allowing the periods of high voltage to be deemed as transient. Accordingly, if the device is unearthed, or not grounded to the earth, the device may nevertheless obtain listing by a certifying and testing organization without being subjected to abnormal testing and possible failure thereof.