Isolated voltage detection with current limiters
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Solution Overview
Problem
Traditional voltage detection circuits in aircraft ovens experience runaway currents due to exponential power increase with input voltage, lacking improved voltage tolerance and precision.
Innovation Solution
An isolated voltage detection circuit using an optical coupling with a Zener diode and current limiter, comprising a MOSFET switching component and multiple resistors, to control current flow and maintain galvanic insulation, allowing consistent current above a threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional voltage detection circuits use resistors to limit current, then the circuit can detect voltage above a threshold, but power increases exponentially with input voltage causing runaway currents
Solution Approach 1:
The patent introduces a current limiter circuit as an intermediary component between the voltage input and the Zener diode/LED assembly. This current limiter actively regulates and caps the maximum current flowing through the optical coupling components, preventing exponential power increase while still allowing the circuit to detect voltage thresholds reliably. The current limiter acts as a mediator that decouples the direct relationship between input voltage and power consumption.
2Measurement precision
If a Zener diode is used to define minimum voltage threshold, then voltage detection precision is improved, but the circuit only responds to half the sine wave due to reverse current blocking
Solution Approach 1:
The patent extracts the reverse current blocking function from the Zener diode by introducing a dedicated diode component positioned in parallel with the optical coupling assembly. This separate diode handles the reverse current path, allowing the Zener diode to focus solely on voltage threshold regulation without being constrained by reverse current blocking requirements. This functional separation enables full-wave sine wave response while maintaining precise threshold detection.
3Reliability
If optical coupling is used to provide galvanic insulation, then safety is improved, but current control precision deteriorates due to lack of consistent current above threshold voltage
Solution Approach 1:
The patent implements feedback control through the current limiter circuit, which continuously monitors and adjusts the current flowing through the optical coupling components. The current limiter uses feedback from the circuit's operating state to maintain consistent current levels above the threshold voltage, ensuring that the optical coupling operates in a stable, predictable regime. This feedback mechanism preserves galvanic insulation while improving measurement precision by eliminating current variability.
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 circuit achieves increased precision in voltage detection and higher voltage tolerance without runaway currents, ensuring reliable operation across varying input voltages.
Implementation Method 1
an optical coupling including an illuminator optically coupled to an optical sensor to output a voltage from the optical sensor based on intensity of illumination from the illuminator
Implementation Method 2
The Zener diode is oriented to block current from the voltage input node through the resistance below a threshold voltage, and to allow current from the voltage input node through the resistance above the threshold voltage
Implementation Method 3
The current limiter can include a switching component with a drain connected to the voltage input node. The current limiter can include a source connected to a first node in series between the Zener diode and the resistance and a gate connected to a second node in series between the resistance and the first node. The switching device can be a MOSFET.
Implementation Method 4
The illuminator can be a light emitting diode (LED) connected in series between the first voltage input node and the second voltage input node
Data Source
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AI summary
A circuit comprises an optical coupling (102) including an illuminator (104) optically coupled to an optical sensor (106) to output a voltage from the optical sensor based on intensity of illumination from the illuminator. The circuit includes a voltage input node (108) with a resistance (110) connected in series between the voltage input and a Zener diode (112). A method includes powering an illuminator with current from a first voltage input node. The method includes sensing illumination level in illumination from the illuminator with a sensor and outputting output proportionate to illumination sensed by the sensor indicative of voltage detected at the voltage input node. The method can include limiting current between the voltage input node and the illuminator.