Low-power Input Circuit with Active Current Limiter
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Solution Overview
Problem
Industrial control systems face challenges in reducing power dissipation and accommodating a wide range of input voltage levels without activating optical isolators by leakage current, which requires specialized isolators and increases power dissipation.
Innovation Solution
A high gain comparator-type regulator system with an active current limiter and an optical isolator bypass circuit that shunts leakage current around the optical isolator, allowing the use of lower power dissipation optical isolators and providing flexible current regulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a series-limiting resistor is used to accommodate wide input voltage range, then voltage compatibility is improved, but multiple I/O modules are required for different applications increasing device complexity
Solution Approach 1:
The patent implements a universal I/O module design using an active current limiter circuit that can accommodate a wide input voltage range (5V to 30V+) through active regulation rather than passive resistance. This single module design replaces the need for multiple specialized modules, achieving universality across different voltage applications.
Solution Approach 2:
The active current limiter dynamically adjusts its resistance parameter based on the input voltage level, transforming from a fixed resistance approach to a variable resistance approach. This allows the same circuit to adapt to different voltage ranges by changing its effective resistance, enabling wide voltage compatibility in a single module.
2Reliability
If optical isolators with larger activation currents are used to prevent leakage current activation, then reliability is improved, but power dissipation increases
Solution Approach 1:
The active current limiter employs feedback control to continuously monitor and regulate the current flowing through the optical isolator. This feedback mechanism ensures that leakage current remains below the activation threshold while allowing precise control of the current level, preventing false activation without requiring oversized isolators.
Solution Approach 2:
The patent replaces the passive mechanical selection of isolators with large activation currents with an active electronic control system. The active current limiter uses electronic regulation to prevent false activation, substituting the need for mechanically selected high-threshold isolators with a dynamically controlled current source.
3Adaptability or versatility
If active current regulation is implemented to accommodate wide voltage range, then adaptability is improved, but power dissipation increases due to I²R losses
Solution Approach 1:
The active current limiter transforms the static resistance approach into a dynamic control system that actively adjusts current based on input voltage. This dynamic regulation allows the circuit to maintain optimal current levels across varying voltages, improving adaptability while managing power dissipation through intelligent control rather than fixed resistance.
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 significantly reduces power dissipation by stabilizing current limiting and allowing the use of lower power optical isolators, enhancing the flexibility in selecting isolators and reducing heat generation across a wide voltage range.
Implementation Method 1
an optical isolator (optoisolator/optocoupler) which provides an electrically actuated light source (an LED) insulated and electrically isolated from a photodetector
Implementation Method 2
a photodetector (for example, a photodiode), the latter of which communicates with the remainder of the industrial control system
Implementation Method 3
providing a current path between the input terminals; and an active current limiter in the current path with the optical isolator to limit current flow through the optical isolator, the active current limiter providing a comparator comparing a voltage drop of a sensing resistor in series with the optical isolator to a fixed voltage reference
Data Source
AI summary
An input circuit for an I/O module for an industrial controller or the like provides a shunt regulator for precisely controlling the maximum current through the LED of an optical isolator. Substantial improvement in the current regulation decreases power dissipation in the optical isolator element. A low voltage shunt circuit prevents leakage from the shunt regulator from activating the optical isolator at low voltages allowing more sensitive optical isolators providing additional power dissipation savings.