Bidirectional MOSFET AC Dimmer With Floating Optocoupled Control
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Solution Overview
Problem
Existing electrical control systems for AC power management in facilities are inefficient and prone to electrical noise, especially when controlling large loads, and lack reliable, cost-effective semiconductor-based solutions for nuanced control like dimming and phase control.
Innovation Solution
A bidirectional power MOSFET switch configuration with a novel floating control circuit using rectifying diodes and an optically coupled phototransistor to control the switching action, allowing for both on-off and phase-control of AC power, integrated with advanced semiconductor devices for efficient and reliable power management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If triacs are used for phase control of AC power, then cycle-by-cycle control capability is improved, but efficiency deteriorates and electrical noise is generated
Solution Approach 1:
The patent replaces triacs (electromechanical devices) with power MOSFETs (solid-state devices) for AC power control. This substitution eliminates the inefficiencies and electrical noise associated with triacs while maintaining phase control capability through electronic switching of the MOSFETs in synchronization with the AC waveform.
Solution Approach 2:
The patent changes the switching parameters by using power MOSFETs with very low on-resistance compared to triacs. The MOSFETs are switched on and off in phase with the AC waveform, achieving efficient control with minimal power loss and no electrical noise generation.
2Loss of energy
If power MOSFETs are used for efficient AC control, then efficiency is improved, but device complexity increases due to bidirectional switching requirements
Solution Approach 1:
The patent segments the bidirectional switching function into two separate unidirectional power MOSFETs connected in series. Each MOSFET handles one polarity of the AC waveform, simplifying the control circuitry while maintaining efficient bidirectional power control. This segmentation avoids the complexity of true bidirectional MOSFETs.
Solution Approach 2:
The patent introduces a control circuit with optocouplers as an intermediary between the control signal and the power MOSFETs. This optically isolated control system provides the necessary gate drive signals while electrically isolating the low-voltage control side from the high-voltage power side, simplifying the overall system architecture.
3Device complexity
If mechanical switches are used for on-off control, then simplicity is improved, but reliability deteriorates due to wear and arcing
Solution Approach 1:
The patent replaces mechanical switches with power MOSFETs for on-off control of AC loads. This substitution eliminates mechanical wear, contact arcing, and the associated reliability issues while maintaining the simple on-off switching function. The solid-state MOSFETs have no moving parts and can withstand millions of switching cycles.
4Adaptability or versatility
If rheostats or autotransformers are used for nuanced control, then control range is improved, but efficiency deteriorates significantly
Solution Approach 1:
The patent replaces rheostats and autotransformers with power MOSFET-based phase control for nuanced adjustment of AC power delivery. This substitution achieves the same control range through electronic switching of the MOSFETs in phase with the AC waveform, eliminating the excessive power losses inherent in resistive and transformer-based control methods.
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 a highly efficient and reliable control system for AC power management, enabling both on-off and phase-control capabilities, reducing electrical noise and improving safety, while being cost-effective and suitable for broad applications in facility electrical systems.
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
rectifying diodes connected at the drains to precharge the gate-source bias voltage thereby turning both devices on
Data Source
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AI summary
A bidirectional switch for the control of power from an AC source to a load is described. The approach 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 boost circuit is included to ensure that the control voltage exceeds a threshold voltage of the MOSFETs to force an off state. A plurality of subcircuits can be easily cascaded to provide improved performance.