Bidirectional MOSFET Switch Topology for Isolated Low-Loss Multiplexing
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Solution Overview
Problem
Existing bidirectional MOSFET switch circuits face challenges in efficiently switching high-voltage signals due to high control current requirements, potential superposition with signal current, and complex galvanic isolation, which complicates construction and increases power losses in multiplexers.
Innovation Solution
A bidirectional MOSFET switch topology using a FET transistor to generate a gate voltage between the gate and source terminals of two MOSFET transistors, with a floating voltage source and potential isolator to isolate control current, allowing for low control current operation and efficient switching, especially for AC signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If photovoltaic driving is used to provide galvanic isolation, then control current is isolated from signal current, but a relatively high control current is required which must primarily supply the LED, resulting in high power losses
Solution Approach 1:
The patent replaces the photovoltaic LED-driving mechanism with a capacitive coupling mechanism. Instead of using an LED to transfer control energy across the isolation barrier, the invention uses capacitors to couple the control signal, eliminating the need for high control currents and associated power losses while maintaining galvanic isolation.
Solution Approach 2:
The invention changes the parameter of control current magnitude by transitioning from a photovoltaic system requiring high currents to a capacitive coupling system that operates with low control currents. This parameter change directly reduces power losses while preserving the galvanic isolation function.
2Reliability
If photovoltaic driving with LED is used, then galvanic isolation is achieved, but a relatively large amount of energy is required to compensate for losses, leading to high power losses in multiplexer arrangements
Solution Approach 1:
The patent substitutes the energy-intensive photovoltaic LED system with an energy-efficient capacitive coupling system. The capacitors transfer control signals with minimal energy loss, dramatically reducing the energy consumption required for galvanic isolation in multiplexer arrangements.
3Loss of energy
If capacitive driving with two small capacitors is used, then low control current is achieved, but only AC signals can be transmitted which have to be rectified again
Solution Approach 1:
The patent enhances the versatility of the capacitive driving system by incorporating a rectification circuit that enables the system to handle both AC and DC signals. The capacitors perform their primary coupling function for AC signals while the integrated rectification capability allows DC signal transmission, making the system universally applicable to various signal types.
4Reliability
If transformer driving is used, then galvanic isolation is achieved, but only AC signals can be transmitted which have to be rectified on the secondary side
Solution Approach 1:
The patent extracts the essential function of galvanic isolation from the complex transformer system and implements it using simple capacitors. By removing the transformer and its associated rectification requirements, the invention achieves galvanic isolation with a much simpler construction that supports both AC and DC signals.
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 solution enables rapid switching of MOSFET transistors with reduced control current and power losses, improving scalability and packing density in multiplexers by decoupling control and signal currents and simplifying construction.
Implementation Method 1
a potential isolator; a control input terminal connected to the control unit via the potential isolator; the potential isolator being configured to galvanic isolate the control input terminal from the control unit
Implementation Method 2
a third FET transistor configured to generate, depending on a control current, a gate voltage Vgs between the first and second gate terminals and the first and second source terminals to switch the first and second MOSFET transistors
Implementation Method 3
a floating voltage source galvanically connected to the input terminal and configured to generate a gate control current for the first and second MOSFET transistors
Data Source
AI summary
A bidirectional MOSFET switch is provided. The switch includes an input terminal, an output terminal and two MOSFET transistors which are connected to one another by their source and gate terminals. The input and the output terminals are connected to a respective drain terminal of the two MOSFET transistors. The switch further includes a control input terminal that is galvanically isolated by a potential isolator and connected to a control unit configured to switch a control current for a FET transistor via a further MOSFET transistor. The FET transistor is configured to generate, by the control current, a gate voltage Vgs between the gate and the source at the two MOSFET transistors for the switching thereof, and a floating voltage source, which is galvanically connected to the input and which is configured to generate a gate control current for the two MOSFET transistors.