Linear Bypass Circuit for LED String Dimming and EMI Reduction
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Solution Overview
Problem
Conventional LED dimming methods are inefficient, introduce electromagnetic interference (EMI), and fail to mimic the color temperature change of incandescent bulbs, resulting in poor light quality and increased costs due to the need for additional components to filter EMI.
Innovation Solution
An electrical circuit with a first and second LED string, each coupled with a linear-mode transistor and a bypass transistor, allowing for controlled dimming and color temperature adjustment by varying the gate voltages of the transistors, which minimizes EMI and eliminates the need for inductors, enabling efficient dimming that mimics incandescent bulb behavior.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If switch-mode transistors are used to modulate LED string output, then color control and dimming function are achieved, but electromagnetic interference (EMI) is introduced and efficiency is reduced
Solution Approach 1:
The patent removes the switching transistor component from the LED driver circuit entirely, replacing it with a linear mode transistor. This extraction of the switching element eliminates the primary source of EMI while maintaining the dimming and color control functions through analog voltage regulation of the linear transistor's gate terminal.
Solution Approach 2:
The patent substitutes the mechanical switching action of switch-mode transistors with an electronic field-effect control mechanism using linear mode transistors. Instead of rapid on/off switching that generates EMI, the system uses continuous analog voltage control of the linear transistor's conductivity, achieving the same dimming and color mixing effects without electromagnetic interference.
2Adaptability or versatility
If switch-mode transistors are used to modulate LED string output, then color control and dimming function are achieved, but efficiency is reduced due to duty cycling
Solution Approach 1:
The patent implements continuous current flow through the LED strings by using linear mode transistors that regulate current continuously rather than through intermittent duty cycling. The linear transistor maintains a continuous conductive path, allowing current to flow steadily at varying levels, which eliminates the efficiency losses associated with repeatedly starting and stopping current flow in switch-mode approaches.
Solution Approach 2:
The patent changes the operating parameter of the transistor from switching mode (binary on/off states) to linear mode (continuous conductivity variation). By controlling the gate voltage of the linear transistor, the system continuously adjusts the current magnitude through the LED strings, achieving dimming and color control through parameter modulation rather than duty cycle variation, thereby maintaining higher efficiency.
3Illumination intensity
If conventional dimming approaches are used, then light intensity is reduced, but color temperature does not shift to mimic incandescent bulb behavior
Solution Approach 1:
The patent applies different control strategies to different LED strings with different color characteristics. By independently controlling the current through warm-white LED strings versus cool-white LED strings using separate linear mode transistors, the system creates a local quality difference in the light output. This allows the overall color temperature to shift toward warmer tones during dimming, mimicking incandescent behavior, while maintaining precise control over each string's contribution to the total light output.
4Object-generated harmful factors
If switch-mode transistors and filtering components are used, then EMI is filtered, but device complexity and parts cost increase
Solution Approach 1:
The patent extracts and removes the entire class of EMI filtering components (inductors, capacitors, shields) from the circuit by eliminating the switching transistor that generates EMI in the first place. This extraction approach is more effective than adding filters because it addresses the root cause, simplifying the circuit to essentially just the linear mode transistor, LED strings, and control circuitry without any passive filtering elements.
Data Source
AI summary
An electrical circuit for driving a light emitting diode (LED) string is described. The electrical circuit includes a first LED string having one or more color LED strings. A first current control transistor is coupled in series with the first LED string. A color bypass transistor may couple in parallel to one of the one or more color LED strings. A second LED string may also be coupled to the first LED string at an anode terminal of both LED strings. The second LED string may be coupled in parallel with a string bypass transistor and in series with a second current control transistor. Connection interfaces to control terminals of the first current control transistor, the color bypass transistor, the second current control transistor, and the string bypass transistor enable a control device to operate these transistors in linear mode to drive the LED strings.