Bidirectional MOSFET Switch with Optocoupler Control for AC Dimming
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing electrical control systems for AC power management in facilities are inefficient and prone to wear, causing short circuits and electrical noise, and lack advanced control options for nuanced appliance control.
Innovation Solution
A bidirectional power MOSFET switch configuration with an optically coupled, floating control circuit that uses rectifying diodes and phototransistors to control power MOSFETs, enabling both on-off and phase-control of AC mains waveform, reducing 'on' resistance and 'off' leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mechanical outlets and switches are used for AC power control, then simple on-off control is provided, but the devices wear out over time causing short circuits and arcing
Solution Approach 1:
The patent replaces mechanical switches and outlets with solid-state electronic control devices including triacs, transistors, and integrated circuits. These electronic components eliminate mechanical wear, arcing, and contact degradation, providing reliable on-off and phase control without the deterioration issues inherent in electromechanical systems.
2Adaptability or versatility
If triacs are used for phase control of AC mains waveform, then cycle-by-cycle control is achieved, but electrical noise is induced back into the facility electrical system
Solution Approach 1:
The patent introduces optocouplers and isolated optical sources as intermediary components between the control circuitry and the power switching elements. These optically coupled devices provide electrical isolation, preventing noise induction into the facility electrical system while maintaining precise phase control capability through light-mediated signal transmission.
3Adaptability or versatility
If triacs or rheostats are used for appliance control, then some control capability is provided, but the devices are too inefficient for small enclosures controlling large electrical loads
Solution Approach 1:
The patent employs power MOSFETs and IGBTs with controllable on-resistance parameters, allowing efficient control of large electrical loads. These devices can be adjusted to maintain low resistance during conduction, minimizing I²R losses, and can be configured in various topologies (single-switch, dual-switch, three-switch) to optimize efficiency for different load types and enclosure sizes.
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 provides reliable, efficient control of AC power with reduced electrical noise and improved safety, allowing for advanced power management functions and low-cost manufacturing.
Implementation Method 1
an optically coupled phototransistor that shorts the gate terminals to the common source terminal to force the devices into their 'off' state when illuminated by an isolated optical source
Implementation Method 2
a novel floating control circuit is employed that uses rectifying diodes connected at the drains to precharge the gate-source bias voltage thereby turning both devices 'on'
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A novel approach for the control of AC power uses power MOSFETs in a bidirectional switch subcircuit configuration having an optically coupled, electrically floating control circuit that self-biases the switches into the "on" state and uses an optically coupled control element to force the switches into the "off state. The time constant of the control circuit is fast enough to allow phase control as well as on-off control. A plurality of subcircuits can be easily cascaded to provide improved performance.