LED Current Control Using Adjustable DC Supply and Feedback
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Solution Overview
Problem
LED lighting systems face inefficiencies due to uncertainties in forward voltages and current flow, leading to reduced energy efficiency and potential damage to LEDs, particularly when current exceeds maximum allowable levels, and there is a need for effective monitoring and control of current without compromising system efficiency.
Innovation Solution
A method and apparatus that utilize a constant voltage power supply with an adjustable DC supply voltage, where a controller determines the current level and communicates this information to adjust the DC supply voltage, using a current sense circuit with transistors to minimize power loss and accurately measure current while maintaining efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the current flowing through the LEDs exceeds a maximum allowable level, then the LEDs may be damaged or permanently burnt out, but reducing the current limits the maximum light output and energy efficiency
Solution Approach 1:
The patent implements a feedback control system that continuously monitors the current flowing through the LEDs and adjusts the drive signal accordingly. The controller receives feedback about actual current levels and modulates the PWM duty cycle to maintain current within safe operating limits while maximizing light output, thus preventing damage without unnecessarily limiting productivity
Solution Approach 2:
The system dynamically adjusts the PWM duty cycle based on real-time current measurements and LED characteristics. Rather than using a fixed current limit, the controller adaptively modifies operating parameters to optimize both safety and performance under varying conditions, allowing maximum light output within safe current boundaries
2Manufacturing precision
If narrow binning criteria are used to ensure consistent light output, then manufacturing precision improves, but the cost of LEDs increases
Solution Approach 1:
The system performs self-characterization by automatically measuring the forward voltage and other parameters of each LED during manufacturing or initial operation. This self-service approach eliminates the need for expensive manual binning processes while ensuring each LED operates at its optimal parameters, achieving consistency without high costs
Solution Approach 2:
The controller dynamically adjusts operating parameters such as PWM duty cycle and drive current based on the specific electrical characteristics of each LED. By adapting to individual LED variations rather than requiring uniform LEDs, the system achieves consistent light output while accommodating a broader range of lower-cost LED components
3Ease of operation
If a constant voltage power supply is used with adjustable DC supply voltage, then the ability to control current flow improves, but the complexity of the power supply system increases
Solution Approach 1:
The system uses feedback from current sensing circuits to automatically regulate the constant voltage power supply output. The controller monitors current flow and adjusts the power supply voltage accordingly, providing precise current control while maintaining a relatively simple power supply architecture that relies on feedback rather than complex active regulation
4Adaptability or versatility
If the forward voltage of LEDs varies due to manufacturing differences, then adaptability to different LED batches improves, but the precision of current control worsens
Solution Approach 1:
The system performs preliminary characterization of each LED or LED string by measuring forward voltage and other parameters before normal operation. This advance knowledge is stored and used to pre-calculate optimal PWM duty cycles and drive parameters, ensuring precise current control is maintained across different LED batches without requiring real-time complex calculations
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 solution enables precise control of current flow through LEDs, preventing damage and optimizing energy efficiency by allowing for automatic or manual adjustment of the DC supply voltage, thereby ensuring consistent light output and extending LED lifespan.
Implementation Method 1
a current sense circuit 106 may be included within the lighting apparatus 200. The current sense circuit 106 may comprise a current sense resistor 108
Implementation Method 2
two current sense control transistors 1101, 1102. The current flowing through the LEDs may be determined by the controller 204 without substantially decreasing the efficiency of the overall lighting apparatus 200
Implementation Method 3
Light Emitting Diodes (LEDs) are increasingly being adopted as general illumination lighting sources
Implementation Method 4
The LCC signal may be a pulse width modulation (PWM) signal
Data Source
AI summary
Methods and apparatus for changing a DC supply voltage applied to a lighting circuit are disclosed. In specific cases, a constant voltage power supply is used to power an LED lighting circuit in which there are uncertainties within the forward voltages of the LEDs, which in turn creates uncertainty with respect to the current level flowing through the LEDs. To manage these uncertainties, the current flowing through the LEDs is measured and an indication of the current level is communicated to a person who can manually adjust the DC voltage supply applied to the LED lighting apparatus by the constant voltage power supply. Alternatively, an automatic adjustment of the DC voltage supply applied to the LED lighting apparatus by the constant voltage power supply can be performed based upon the measured current level.