LED Current Mirror Circuit for Dim-to-Warm CCT Control
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Solution Overview
Problem
Existing solid-state lighting systems face challenges in efficiently controlling correlated color temperature (CCT) across multiple LED strings, particularly in achieving a 'dim-to-warm' performance without complex control circuitry.
Innovation Solution
The use of a current mirror circuit with a bypass circuit, allowing for proportional control of current levels between LED strings, including blue-shifted yellow (BSY) LEDs, to produce different CCTs, and a bypass mechanism using resistors or switches to activate/deactivate the current mirror circuit, enabling simple control of lighting output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple LED strings with different CCTs are used to achieve dim-to-warm performance, then lighting output characteristics can be controlled, but control circuitry complexity increases
Solution Approach 1:
The patent uses a current mirror circuit to copy the current from the first LED string to the second LED string. The current mirror circuit replicates the current waveform and characteristics from one string to another, enabling coordinated control of multiple LED strings with different CCTs without requiring complex independent control circuitry for each string.
Solution Approach 2:
The current mirror circuit serves multiple functions simultaneously: it acts as a current regulator, a synchronization device, and a control mechanism for achieving dim-to-warm performance. By making the control circuitry multi-functional, the patent reduces overall system complexity while maintaining the ability to control lighting output characteristics.
2Adaptability or versatility
If current levels in multiple LED strings are proportionally controlled, then CCT variation can be achieved, but control mechanism complexity increases
Solution Approach 1:
The current mirror circuit copies the current characteristics from the first LED string to the second LED string, automatically establishing a proportional relationship between the current levels. This copying mechanism enables CCT variation through simple current proportioning rather than complex control algorithms.
Solution Approach 2:
The current mirror circuit automatically regulates the current distribution between LED strings based on the inherent properties of the mirror circuit itself, without requiring external control signals or complex feedback mechanisms. The circuit self-adjusts to maintain the desired current proportionality for CCT variation.
3Ease of operation
If LED strings are driven by PWM control, then lighting output can be controlled, but heat generation and efficiency are reduced compared to DC control
Solution Approach 1:
The patent replaces PWM (electrical switching) control with DC control through current mirror circuits. Instead of using pulse-width modulation that generates heat and energy loss, the system uses continuous DC current control via the current mirror mechanism, which is more efficient and generates less heat while still providing precise control over lighting output.
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 approach allows for effective control of lighting output characteristics, approximating incandescent lamp behavior by varying CCT in response to dimming, with reduced complexity in control circuitry and improved temperature tracking across LED strings.
Implementation Method 1
a current control circuit coupled to second terminals of the first and second strings of LEDs and configured to vary a proportionality relationship between current levels in the first and second strings of LEDs
Implementation Method 2
a bypass circuit coupled to the second string of LEDs and configured to bypass the second current path of the current mirror circuit
Implementation Method 3
a first string of light-emitting diodes (LEDs) having a first terminal coupled to a current source and configured to produce a first correlated color temperature (CCT)
Data Source
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Figure 3~4
AI summary
Lighting apparatus includes a first string of light-emitting diodes (LEDs) having a first terminal coupled to a current source and configured to produce a first correlated color temperature (CCT) and a second string of LEDs having a first terminal coupled to the current source and configured to produce a second CCT different from the first CCT. The lighting apparatus further includes a current control circuit coupled to second terminals of the first and second strings of LEDs and configured to vary a proportionality relationship between current levels in the first and second strings of LEDs responsive to variation in a current provided by the current source to the first terminals of the first and second strings of LEDs. The current control circuit may include a current mirror circuit and a control circuit configured to selectively enable and disable the current mirror circuit.