Variable Emitter Resistor for Multi-Channel LED Current Control
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Solution Overview
Problem
Conventional apparatuses for controlling constant current in multi-channel LEDs result in high power consumption and heat generation due to forward voltage differences between LED channels, making it difficult to integrate transistors within an integrated circuit (IC).
Innovation Solution
The apparatus includes a plurality of LED channels with transistors and variable emitter resistors, a feedback sensing circuit, and a controller that adjusts the emitter resistance of LED channels with higher collector voltages to reduce power consumption by increasing the emitter resistance in response to feedback sensing results.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a DC-DC converter outputs a voltage high enough to drive LED channels with higher forward voltage, then all LED channels can be driven, but transistors require larger channel capacity and higher power consumption
Solution Approach 1:
The patent applies dynamics by making the emitter resistance variable rather than fixed. The emitter resistance is dynamically adjusted based on the forward voltage of each LED channel, allowing the transistor to operate efficiently across different voltage conditions. This dynamic adjustment reduces the required channel capacity and power consumption of the transistor while maintaining the ability to drive multiple LED channels with different forward voltages
Solution Approach 2:
The patent changes the resistance parameter of the emitter resistor from a fixed value to a variable value that can be adjusted according to the LED channel's forward voltage. By changing this parameter dynamically, the system achieves adaptability to different LED channels without requiring oversized transistors, thus reducing power consumption while maintaining versatility
2Reliability
If transistor channel capacity is increased to handle voltage differences, then constant current control is maintained, but transistor size increases and integration into IC becomes difficult
Solution Approach 1:
The patent uses dynamic adjustment of emitter resistance to maintain reliable constant current control without requiring large transistor channel capacity. The variable emitter resistance compensates for voltage differences across LED channels, allowing smaller transistors to achieve the same current control reliability that would otherwise require oversized devices
Solution Approach 2:
The variable emitter resistance acts as an intermediary element between the transistor and the LED channel. It mediates the voltage differences and current variations, allowing the transistor to operate with smaller channel capacity while still maintaining reliable constant current control. This intermediary component enables IC integration by reducing the transistor size requirement
3Device complexity
If fixed emitter resistance is used for constant current control, then circuit simplicity is maintained, but power consumption varies significantly across LED channels
Solution Approach 1:
The patent transitions from a static fixed emitter resistance to a dynamic variable emitter resistance that adjusts based on the LED channel's forward voltage. This dynamic approach reduces power consumption variations across different LED channels while adding minimal circuit complexity through the use of a controllable resistor element
Solution Approach 2:
The patent implements feedback control where the emitter resistance is adjusted based on sensing the actual current or voltage conditions in each LED channel. This feedback mechanism ensures that power consumption is optimized for each channel's specific requirements, reducing overall power variation while maintaining constant current control
Data Source
AI summary
An apparatus for controlling the constant current for multi-channel LEDs includes: a plurality of LED channels each comprising an LED array, a transistor, and a variable emitter resistor; a feedback sensing circuit for sensing the collector or drain voltage of a transistor of each of the LED channels; and a controller for increasing the variable emitter resistance of an LED channel in which the collector voltage of the transistor is higher than those of the other LED channels, in response to a feedback sensing result input from the feedback sensing circuit.