Semiconductor Relay Isolation Circuit for Safe AC Load Switching
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Solution Overview
Problem
Existing control systems for safe outputs in functional safety applications lack effective galvanic isolation between control and power circuits, particularly for bidirectional power lines and AC switching, and do not adequately address issues like reverse polarity and fault detection.
Innovation Solution
The implementation of galvanically isolated control and power circuits using inductive, optical, or capacitive coupling, with additional components like rectifier diodes, capacitors, and Zener diodes to manage voltage and current, and the use of auxiliary switches for independent testing and error detection, allowing for redundant switching paths and overload protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mechanical relays are used for switching, then simple switching function is achieved, but galvanic isolation between control and power circuits is not provided
Solution Approach 1:
The patent replaces mechanical relay contacts with solid-state switching elements (transistors, IGBTs, MOSFETs) that provide galvanic isolation through semiconductor junctions and oxide layers, eliminating the need for mechanical movement while maintaining switching functionality and providing inherent electrical isolation between control and power circuits
Solution Approach 2:
The patent introduces isolated gate drivers as intermediary devices that receive control signals on the low-voltage side and generate isolated switching signals for the high-voltage side through galvanic isolation barriers (optocouplers, transformers, or capacitive couplers), enabling safe signal transmission across isolated boundaries
2Reliability
If field effect transistors are used for switching, then unidirectional current control is achieved, but reverse polarity protection is lacking
Solution Approach 1:
The patent combines field effect transistors with anti-parallel diodes in a single switching module, where the diode provides reverse polarity protection by conducting current in the opposite direction, effectively creating a bidirectional switching capability while maintaining the advantages of FET control
Solution Approach 2:
The patent designs switching elements that serve multiple functions: the FET provides controlled switching in the forward direction, while the anti-parallel diode provides both reverse polarity protection and freewheeling path for inductive loads, reducing the need for additional protective components
3Reliability
If redundant switching elements are added for testing, then individual switch testing capability is improved, but device complexity increases
Solution Approach 1:
The patent incorporates test functionality that can detect switch status and faults during normal operation without requiring separate test modes or disrupting the switching sequence, allowing continuous monitoring and immediate fault detection while maintaining system operation
Solution Approach 2:
The patent implements self-diagnostic capabilities where the switching elements and control circuitry monitor their own status through built-in sensing mechanisms, automatically detecting faults and reporting switch status without requiring external test equipment or complex test procedures
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 approach ensures reliable galvanic isolation, reduces the risk of dangerous failures, and provides effective fault detection and protection against overloads, enhancing the safety and efficiency of control systems in functional safety applications.
Implementation Method 1
Inductive coupling has the advantage of transferring energy from the control side to the control side
Implementation Method 2
optical coupling (optocoupler principle)
Implementation Method 3
capacitive coupling
Data Source
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AI summary
A safety switching device, designed for the safe switching on and off of an electrical load in accordance with a safety regulation, comprising a power circuit with at least two series-connected semiconductor switching elements (S1, S2), an output (K2) to which the electrical load (RL25) can be connected by forming a supply circuit for the electrical load that can be safely switched by means of the semiconductor switching elements (S1, S2), further comprising a measuring and evaluation system for testing the functionality of the semiconductor switching elements by means of voltage measuring devices, designed to measure the voltage across the respective semiconductor switching element (S1, S2), is intended to enable galvanic isolation of the power circuits from each other.It has a switching element (S3) for forming a current path parallel to the consumer (RL25), which includes the semiconductor switching elements, and the switching contacts of the semiconductor switching elements are galvanically isolated (TR1-TR3).