Bidirectional MOSFET Switch with Floating Control Circuit
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Solution Overview
Problem
Conventional electrical control systems for AC power management in facilities are inefficient and prone to electrical noise, especially when controlling large loads, and lack reliable bidirectional switching capabilities, which can lead to safety issues and inefficiencies.
Innovation Solution
A bidirectional power MOSFET switch configuration with a novel floating control circuit using rectifying diodes and optically coupled phototransistors to control the switching action, allowing for both on-off and phase-control of AC mains waveform, integrated with advanced semiconductor devices for efficient and reliable power management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If triacs are used for phase control of AC mains waveform, then cycle-by-cycle control efficiency is improved, but electrical noise is induced back into the facility electrical system and the devices are too inefficient for controlling large electrical loads in small enclosures
Solution Approach 1:
The patent replaces traditional triac-based phase control with a solid-state electronic switching system using MOSFETs and optoelectronic components. This substitution eliminates the electrical noise generation inherent in triac operation while maintaining efficient cycle-by-cycle AC waveform control capability, resolving the contradiction between control efficiency and noise generation.
Solution Approach 2:
The patent introduces optoelectronic intermediaries (optocouplers, photodetectors, LED drivers) as mediators between the control circuitry and the power switching elements. This intermediary layer isolates the control signals from the high-power AC switching, preventing electrical noise from being induced back into the facility electrical system while preserving precise phase control functionality.
2Ease of operation
If electromechanical switches are used for control of conventional electrical appliances, then simple on-off control is provided, but the devices wear out over time and can cause short circuits or potentially dangerous arcing
Solution Approach 1:
The patent replaces electromechanical switches with solid-state electronic switching components (MOSFETs, optocouplers, photodetectors). This substitution eliminates mechanical wear and arcing problems while maintaining simple on-off control functionality, thereby improving reliability without sacrificing ease of operation.
Solution Approach 2:
The patent implements a control system where the optoelectronic components and microcontroller automatically manage the switching operations based on simple user inputs. The system self-regulates the AC power delivery through electronic phase control, eliminating the need for mechanical moving parts that require maintenance while keeping the interface simple for users.
3Adaptability or versatility
If rheostats or autotransformers are used for control of electrical appliances, then nuanced control is provided, but the devices are too inefficient to be used effectively in small enclosures for controlling large electrical loads
Solution Approach 1:
The patent replaces inefficient rheostats and autotransformers with solid-state electronic switching using MOSFETs controlled by optoelectronic circuits. This substitution provides continuous dimming control (nuanced control) through electronic phase angle control while maintaining high efficiency by minimizing resistive losses, enabling use in compact enclosures for large electrical loads.
Solution Approach 2:
The patent changes the control parameter from resistive voltage division (inefficient) to electronic phase angle control (efficient). By varying the conduction angle of the AC waveform through optoelectronic-triggered MOSFET switching, the system achieves continuous control of power delivery to loads while minimizing energy loss, resolving the contradiction between control versatility and power efficiency.
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 continuous variation of power delivery, reducing electrical noise, and enhancing safety by minimizing leakage currents and power dissipation, suitable for a wide range of applications from simple switching to complex dimming and phase-control scenarios.
Implementation Method 1
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'
Implementation Method 2
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
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