Analog Optocoupler Input Protection for Linear Signal Isolation
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Solution Overview
Problem
Optocouplers face issues with non-linearity in the relationship between input and output due to factors like LED sensitivity and voltage limiter leakage currents, which can lead to variations in the conditioned signal, compromising safety and accuracy in industrial communication systems.
Innovation Solution
An input protection circuit is introduced, comprising a first voltage limiter coupled to an amplifier circuit and a buffer, along with a second voltage limiter and fuses, to ensure a stable and linear output by controlling the voltage applied to the LED and photodiode, preventing voltage exceedance and maintaining a constant current in the photodiode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage limiters are used to protect the LED and photodiode from excessive voltage, then safety and reliability are improved, but leakage currents from the voltage limiters cause non-linearity and signal variations
Solution Approach 1:
The patent removes voltage limiters from the signal path connecting the LED and photodiode, extracting the harmful leakage current effect from the critical signal transmission path. Protection is maintained through other means that do not introduce leakage currents into the signal path.
Solution Approach 2:
The patent introduces an isolation barrier as an intermediary element between the LED and photodiode circuits. This barrier prevents direct electrical connection and eliminates the leakage current path while maintaining signal transmission through optical coupling.
2Power
If the LED current is increased to improve the output signal strength, then the signal-to-noise ratio is improved, but the non-linearity of the LED's light output increases
Solution Approach 1:
The patent employs feedback circuitry that monitors the photodiode output and adjusts the LED current to compensate for non-linearities. This feedback mechanism maintains a linear relationship between input and output signals while allowing the system to operate at optimal signal levels.
Solution Approach 2:
The patent uses dynamic current adjustment where the LED current is continuously varied based on feedback from the photodiode output. This dynamic control allows the system to maintain linearity across different operating conditions and signal levels.
3Stability of the object's composition
If temperature compensation is implemented to address LED sensitivity to temperature, then the stability of light output is improved, but the device complexity increases
Solution Approach 1:
The patent implements self-service temperature compensation where the system uses its own output signal to detect and correct temperature-induced variations. The photodiode output feeds back to adjust the LED drive, creating a self-regulating system that compensates for temperature effects without external intervention.
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 input protection circuit ensures a linear relationship between the input and output signals, preventing voltage exceedance and maintaining a constant current, thus enhancing the reliability and safety of optocoupler performance in industrial applications.
Implementation Method 1
The LED 22 emits light in response to the conditioned signal
Implementation Method 2
A first photodiode 24 and a second photodiode 26 receive the emitted light
Data Source
AI summary
An input protection circuit (110) for an optocoupler (20) is provided. The input protection circuit (110) includes a first voltage limiter (D1) with a first terminal that is electrically coupled to an input terminal of an amplifier circuit (120), wherein the input terminal of the amplifier circuit (120) is configured to receive a PWM signal and the amplifier circuit (120) is configured to provide a voltage to the optocoupler (20).