Solid State Relay Circuit Using Constant-Current Driver Isolation
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Solution Overview
Problem
Electro-mechanical relays are prone to mechanical damage, have low switching speeds, and poor electromagnetic compatibility due to mechanical nature, leading to a trend towards solid state relays, but existing solid state relays with optical isolation are costly.
Innovation Solution
A solid state relay circuit utilizing a relay transistor and a driver circuit with a constant current source, comprising diodes and resistors to switchably operate the relay transistor, reducing costs and improving switching speed and EMC.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If optical isolation is used in solid state relays, then reliability is improved, but cost increases significantly
Solution Approach 1:
The patent removes the opto-coupler component from the solid state relay design, extracting the optical isolation function and replacing it with an alternative electrical isolation approach using a driver circuit with constant current source, thereby reducing cost while maintaining reliability
Solution Approach 2:
The patent replaces the optical isolation mechanism (which requires opto-couplers) with an electrical isolation mechanism using transistor-based driver circuits, substituting one physical principle for another to achieve the same functional goal at lower cost
2Ease of manufacture
If electro-mechanical relays are used, then ease of manufacture is maintained, but switching speed deteriorates
Solution Approach 1:
The patent replaces electro-mechanical relay components with solid state transistor switches, eliminating mechanical moving parts and replacing them with semiconductor-based switching elements that achieve much faster switching speeds while remaining manufacturable
3Ease of operation
If electro-mechanical relays are used, then ease of operation is maintained, but electromagnetic compatibility deteriorates
Solution Approach 1:
The patent replaces electro-mechanical relay operations with solid state transistor switching, eliminating the mechanical armature movement that generates electromagnetic interference, thereby improving EMC while maintaining ease of operation through similar control interfaces
4Reliability
If solid state relays replace electro-mechanical relays, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent applies local quality by using a simplified driver circuit topology with specific component arrangements (constant current source, driver transistor, blocking diode) that provides adequate isolation and control without the complexity of full optical isolation, achieving reliability through targeted design rather than comprehensive complexity
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 solution enables reliable, high-speed switching with improved EMC, reducing costs and thermal issues, and eliminating mechanical wear, making it suitable for safety-critical applications like automotive and IoT.
Implementation Method 1
the diode and the driver transistor are arranged to produce a constant voltage across the first resistor
Implementation Method 2
the driver circuit is configured and arranged to switchably operate the relay transistor, and wherein the relay transistor is configured and arranged to switchably operate the electrical load
Data Source
AI summary
The disclosure relates to solid state relay circuit for switching an electrical load. The solid state relay circuit may include a relay transistor; and a driver circuit comprising a constant current source. The driver circuit is configured and arranged to switchably operate the relay transistor, and the relay transistor is configured and arranged to switchably operate the electrical load.