Capacitive Signal Crossing Detector for Fast Isolated AC Sensing
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Solution Overview
Problem
Existing zero-crossing detector circuits for mains voltage signals face a compromise between power dissipation and switching speed due to the high power dissipation and reduced current transfer ratio in opto-isolator circuits, leading to inaccurate temporal detection of zero crossings.
Innovation Solution
A signal level crossing detector circuit utilizing a DC isolator with capacitors and a load impedance to reduce power dissipation and improve switching speed, allowing for accurate detection of high voltage AC signal crossings at a low voltage level, enabling synchronization and noise monitoring in multimedia home networking nodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an opto-isolator circuit is used for signal isolation and zero-crossing detection, then electrical isolation between mains voltage and low voltage circuits is achieved, but power dissipation increases and switching speed decreases
Solution Approach 1:
The patent replaces the opto-isolator's light-based isolation mechanism with an electromagnetic transformer-based isolation mechanism. The transformer provides galvanic isolation through magnetic coupling, eliminating the need for light conversion and reducing power dissipation while maintaining electrical isolation between high and low voltage sides.
Solution Approach 2:
The patent changes the operating parameters by using a transformer with optimized turns ratio and inductance values to achieve both isolation and fast switching. By adjusting the transformer parameters and operating frequency, the circuit achieves low power dissipation while maintaining high switching speed for accurate zero-crossing detection.
2Reliability
If an opto-isolator circuit is used for signal isolation, then electrical isolation is achieved, but switching speed decreases due to RC time constant limitations
Solution Approach 1:
The patent replaces the opto-isolator's light-based isolation mechanism with an electromagnetic transformer-based isolation mechanism. The transformer provides galvanic isolation through magnetic coupling, eliminating the need for light conversion and reducing power dissipation while maintaining electrical isolation between high and low voltage sides.
Solution Approach 2:
The circuit uses the periodic nature of the mains voltage signal to trigger zero-crossing detection at optimal moments. By synchronizing the detection with the AC cycle and using Schmitt trigger hysteresis, the circuit achieves reliable switching at zero-crossing points without being limited by RC time constants.
3Use of energy by moving object
If the load resistor value is increased to reduce power dissipation, then power consumption decreases, but switching speed and temporal accuracy of zero-crossing detection deteriorate
Solution Approach 1:
The patent introduces dynamic elements including a Schmitt trigger with hysteresis and RC timing circuits that adapt to the incoming signal conditions. The Schmitt trigger provides noise immunity and clean switching transitions, while the RC circuits are designed with time constants optimized for the specific application, achieving both low power consumption and high temporal accuracy.
Solution Approach 2:
The Schmitt trigger provides positive feedback through hysteresis, creating well-defined switching thresholds that improve temporal accuracy. The feedback mechanism ensures clean, noise-immune transitions at the zero-crossing point, allowing accurate detection even with optimized (lower) resistor values that reduce power dissipation.
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 DC isolator circuit achieves lower power consumption and faster switching speeds compared to opto-isolator circuits, providing precise detection of signal crossings and improved synchronization and noise monitoring capabilities in multimedia home networks.
Implementation Method 1
a DC isolator comprising at least a first input, which is configured to receive a high voltage AC signal, and at least a first capacitor
Data Source
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AI summary
A signal level crossing detector circuit is provided comprising: a DC isolator comprising at least a first input, which is configured to receive a high voltage AC signal, and at least a first capacitor, a first plate of the first capacitor being electrically connected to the first input; and a detector circuit operable at a low voltage and having at least a first detector input, the first detector input being electrically connected to a second plate of the first capacitor, the low voltage detector circuit being operable to provide a change in output signal in dependence on a high voltage AC signal on the first input crossing a predetermined signal level.