Line-current-detector

The detection of line-current flow and its indication at an electrically remote point is essential for line status monitoring in various telephone systems and auxiliary systems. The monitoring circuit must minimally unbalance or load the line, while also being able to disregard relatively high levels of 60-Hz induced voltages. The HllAAl component is capable of sensing line currents of either polarity without discrimination and can ignore noise levels up to approximately 2.5 mA. For applications that require greater noise immunity or polarity-sensitive line-current detection, the HllAlO threshold coupler is recommended. This phototransistor coupler is designed to provide a minimum current transfer ratio of 10% at a specified input current, while exhibiting a leakage of less than 50 µA at half that input current across a temperature range of -55°C to +100°C. The input current range, during which the coupler remains active, can be programmed using a single resistor, allowing for adjustment between 5 to 10 mA.

The described circuit is essential for effective monitoring of line-current flow in telephone and auxiliary systems. A key component, the HllAAl, is engineered to detect both positive and negative line currents, ensuring versatility in various applications. Its ability to function without significant loading on the line is critical for maintaining the integrity of the monitored system. The design incorporates a high level of noise immunity, capable of filtering out disturbances up to 2.5 mA, which is particularly beneficial in environments with electromagnetic interference.

For enhanced performance in scenarios where noise levels are elevated or where the polarity of the current is significant, the HllAlO threshold coupler serves as an advanced alternative. This component's phototransistor design allows for precise current transfer, with a minimum of 10% transfer ratio, ensuring reliable signal transmission. The low leakage current specification of less than 50 µA is particularly advantageous in power-sensitive applications, as it minimizes energy loss and heat generation.

The programmability of the input current range through a single resistor provides flexibility. By adjusting this resistor, the user can set the operational range of the coupler between 5 to 10 mA, tailoring the circuit's response to specific application requirements. This feature is crucial for applications that demand precise control over the activation thresholds of the monitoring circuit, allowing it to adapt to varying operational conditions while maintaining optimal performance.

Overall, this monitoring circuit design, featuring the HllAAl and HllAlO components, represents a robust solution for line-current detection, ensuring accurate monitoring and indication of line status across a variety of systems.Detection of line-current flow and indicating the flow to an electrically remote point is required in line status monitoring at a variety of points in theJelephone system and auxiliary systems. The line should be minimally unbalanced or loaded by the monitor circuit, and relatively high levels of 60-Hz induced voltages must be ignored.

The HllAAl allows line currents of either polarity to be sensed without discrimination and will ignore noise up to approximately 2.5 mA. In applications where greater noise immunity or polarity- sensitive line-current detection is required, the HllAlO threshold coupler can be used.

This phototransistor coupler is specified to provide a minimum 10% current transfer ratio at a defined input current, while leaking less than 50 p.A at half that input current over the full -55°C to + 100°C temperature range. The input current range, at which the coupler is on, is programmable by a single resistor from 5 to 10 mA.

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