Switched-Mode Power Supply Feedback Using LED Isolation
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Solution Overview
Problem
Commercially available optocouplers for galvanic isolation in switched-mode power supplies are expensive and result in significant power loss and heat generation when used in feedback paths, making them unsuitable for potentially explosive areas due to high current requirements and voltage drops across series resistors.
Innovation Solution
A switched-mode power supply design that eliminates the series resistor by using a voltage regulator to reduce the supply voltage across the light source and a current regulator to adjust the current flowing through it, incorporating a light-emitting diode with a wavelength-transparent insulator and a phototransistor for signal transmission, allowing for efficient regulation without high power loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a series resistor is used to reduce supply voltage across the light source, then voltage regulation is achieved, but power loss and heat generation increase significantly
Solution Approach 1:
The patent changes the operating parameters by using a light source that operates at lower current (e.g., 1-10 mA instead of 50-100 mA) while maintaining sufficient light transmission through the insulator. This parameter change dramatically reduces power loss in the series resistor from 0.75-1.5 W to much lower values, resolving the contradiction between voltage regulation and energy efficiency
Solution Approach 2:
The patent employs commercially available LEDs and insulators that are inexpensive and can be mass-produced, replacing expensive optocouplers. The simple resistor-LED-insulator configuration uses low-cost components that achieve the same galvanic isolation function without the high power consumption of traditional optocouplers
2Illumination intensity
If high current is used to operate the light source through the insulator, then sufficient light transmission is achieved, but power dissipation and heat generation increase
Solution Approach 1:
The patent changes the current parameter from high (50-100 mA) to low (1-10 mA) while selecting insulators with appropriate optical properties (thickness, material composition) that allow sufficient light transmission at the lower current level. This resolves the contradiction by finding an optimal operating point that maintains light transmission while minimizing power dissipation
3Reliability
If commercially available optocouplers are used for galvanic isolation, then safety requirements are met, but cost and power consumption increase significantly
Solution Approach 1:
The patent segments the optocoupler function into separate components: a light source (LED), a physical insulator barrier, and a light receiver (photodetector). This segmentation allows each component to be optimized independently and selected from inexpensive commercial parts, achieving galvanic isolation without the high cost of integrated optocouplers
Solution Approach 2:
The patent creates a simplified copy of the optocoupler function using basic components (resistor, LED, insulator, photodetector) that replicate the galvanic isolation capability. This component-level copying uses inexpensive, mass-producible parts that achieve the same safety function at much lower cost
4Reliability
If thick insulators are used for galvanic isolation, then safety requirements are met, but light transmission and signal strength decrease
Solution Approach 1:
The patent changes multiple parameters simultaneously: selects insulator materials with high optical transmission properties, optimizes insulator thickness within safety requirements, chooses LEDs with wavelengths and intensities optimized for penetrating the specific insulator material. This multi-parameter optimization resolves the contradiction between isolation distance and light transmission
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 design reduces power loss and heat generation, enabling cost-effective production of switched-mode power supplies suitable for potentially explosive areas while maintaining efficient voltage regulation and safety compliance.
Implementation Method 1
a light source, e.g., an infrared LED, arranged on one side of a printed circuit board
Implementation Method 2
This light source transmits light through the board, which is then received by a light receiver located on the other side of the board
Implementation Method 3
a light receiver located on the other side of the board... that converts the incident light into an electrical signal
Implementation Method 4
a galvanically isolated transformer downstream of the switching regulator
Data Source
Figure 1~2
Figure 3
AI summary
The invention relates to a switched-mode power supply for supplying an output voltage (Uout) controlled to a target value (Us) to a load (S), which switched-mode power supply can be economically produced and is suitable for use in explosion-prone areas, comprising: a supply path, which comprises a switching controller (5) controlled by means of a driver (3), a galvanically separated transformer (7) connected after the switching controller (5), and an output circuit (9), which is connected after the transformer (7) and which comprises a rectifier (11) and to the output of which the load (S) can be connected; and a feedback path, by means of which a signal, which is transmitted by means of a light source (13) and a light receiver (15) and which represents the output voltage (Uout), is fed to the driver (3), on the basis of which signal the driver (3) controls the output voltage (Uout) to the target value (Us) by means of appropriate control of the switching controller (5), which switched-mode power supply is characterized in that the feedback path comprises a voltage controller (19), which controls a feed voltage that drops across the light source (13) to a fixed value lying below the target value (Us), and comprises a current controller (21), which controls a current flowing through the light source (13) to a current value corresponding to the output voltage (Uout).