LED Current Source Modulation for Power Reduction
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Solution Overview
Problem
Current sources for driving LEDs in applications like mobile phone backlights face challenges in optimizing power consumption while maintaining luminous intensity, as existing methods like pulse-width modulation do not efficiently reduce power dissipation at low currents.
Innovation Solution
A current source that extracts first and second current values from a brightness signal, derives a duty cycle value, and modulates the driving current between these values using pulse-width modulation, allowing for reduced average current and increased duty cycle to minimize power consumption while maintaining LED brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If pulse-width modulation is used to control LED brightness, then power consumption is reduced, but current spikes and electromagnetic radiation increase
Solution Approach 1:
The patent applies periodic action by using pulse-width modulation to switch the LED current in periodic cycles between ON and OFF states. The duty cycle of these periodic pulses controls the average brightness while maintaining the LED operating point above zero, thus reducing power consumption through periodic switching rather than continuous operation at low current.
Solution Approach 2:
The patent changes the parameter of LED operating current from traditional approaches that allow current to drop to zero or negative values, to a regime where the operating point is maintained above zero. This parameter change optimizes the balance between power consumption reduction and minimizing harmful current spikes and electromagnetic radiation by avoiding extreme current conditions.
2Use of energy by moving object
If LED current is reduced to lower power consumption, then power dissipation decreases, but luminous intensity may be compromised
Solution Approach 1:
The patent uses periodic pulse-width modulation to deliver current to the LED in cycles rather than continuously. By controlling the duty cycle of these periodic pulses, the average power consumption is reduced while the peak current during ON periods maintains sufficient luminous intensity, achieving the desired brightness with lower overall power dissipation.
Solution Approach 2:
The patent applies dynamics by making the LED current dynamic through pulse-width modulation rather than static continuous current. The current dynamically switches between ON and OFF states with variable duty cycle, allowing the system to adapt power delivery to match required luminous intensity while minimizing average power dissipation through temporal variation in current delivery.
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 reduces power dissipation and maintains LED brightness with lower average current and forward voltage, effectively lowering power consumption and minimizing current spikes and electromagnetic radiation.
Implementation Method 1
at least one light-emitting diode, LED
Implementation Method 2
light-emitting diode, LED
Data Source
Figure 1
Figure 2a~2b
Figure 3~4b
AI summary
In one embodiment a current source comprises an input (In) for receiving a brightness signal (Sb), and an output (Out) for providing a driving current (Id) for at least one light-emitting diode, LED, wherein the current source (CS) is configured to extract a first and a second current value (idac_high, idac_low) from the brightness signal (Sb), to derive a duty cycle value (Smod) from the brightness signal (Sb) and to modulate the driving current (Id) as a function of the duty cycle value (Smod) in a pulse-width modulation comprising the first and the second current values (idac_high, idac_low). Furthermore, a method for providing a current is described.