Capacitive Isolated AC Switch Control Circuit Without Transformers
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Solution Overview
Problem
Existing methods for controlling high-voltage AC switches using low-voltage DC signals require bulky and expensive isolation transformers or pose reliability issues with optocouplers, and existing capacitive solutions only transmit control signals without providing power.
Innovation Solution
A circuit using high-voltage capacitive elements and Schottky diodes to generate a DC signal for controlling an AC switch, where a high-frequency DC pulse signal is used to transfer both control and power across a capacitive isolation barrier, eliminating the need for isolation transformers and simplifying the control circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an isolation transformer is used to control a high-voltage AC switch from a low-voltage DC circuit, then galvanic isolation and user protection are achieved, but the device becomes bulky and expensive
Solution Approach 1:
The patent replaces the mechanical/magnetic isolation transformer with an optoelectronic system using optocouplers. The control signal is transmitted through light transmission across an isolation barrier, eliminating the need for magnetic coupling and large transformer components while maintaining galvanic isolation and user protection.
Solution Approach 2:
The patent introduces optocouplers as intermediary devices that convert electrical control signals into light signals for transmission across the isolation barrier, then convert them back to electrical signals on the other side. This intermediary approach achieves isolation without requiring direct electrical or magnetic coupling.
2Weight of stationary object
If optocouplers are used for isolation, then device size is reduced, but reliability problems occur
Solution Approach 1:
The patent implements a self-diagnostic system where the microcontroller actively monitors the optocoupler performance by measuring the voltage at the optocoupler output during different operational states. The system automatically detects degradation or failure of the optocoupler and can trigger protective actions, making the isolation system self-monitoring and self-protecting.
Solution Approach 2:
The patent incorporates feedback mechanisms where the microcontroller continuously monitors the state of the AC switch and the performance of the optocouplers. This feedback allows the system to detect anomalies in real-time and adjust operation or alert the user, improving overall system reliability through active monitoring.
3Reliability
If a capacitive element transmits control signal, then isolation is achieved, but power transmission for switch triggering is insufficient
Solution Approach 1:
The patent makes the optocoupler system multi-functional by enabling it to perform both control signal transmission and power transmission for AC switch triggering. The isolated DC-DC converter on the high-voltage side generates the necessary triggering power from the control circuit's DC supply, allowing a single isolation interface to handle both functions that previously required separate systems.
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
This solution provides a compact, reliable, and efficient means to control high-voltage AC switches using low-voltage DC signals, offering improved immunity to electromagnetic disturbances and reduced bulk, while effectively transferring both control and power signals.
Implementation Method 1
a first capacitive element connecting a first input terminal, intended to receive the high-frequency signal, to a first terminal of a rectifying element
Implementation Method 2
a rectifying element having its second terminal connected to a first output terminal intended to be connected to a control terminal of the switch
Implementation Method 3
a second capacitive element connecting a second input terminal, intended to be connected to the second reference potential, to a second output terminal intended to be connected to the first reference potential
Data Source
AI summary
A circuit for generating a D.C. signal for controlling an A.C. switch referenced to a first potential, from a high-frequency signal referenced to a second potential, including: a first capacitive element connecting a first input terminal, intended to receive the high-frequency signal, to the cathode of a rectifying element having its anode connected to a first output terminal intended to be connected to a control terminal of the switch; and a second capacitive element connecting a second input terminal, intended to be connected to the second reference potential, to a second output terminal intended to be connected to the first reference potential, a second rectifying element connecting the cathode of the first rectifying element to the second output terminal.