Single Inductor LED Driver With Error Voltage Selection
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Solution Overview
Problem
Conventional switching power supplies face challenges in efficiently driving multiple LED loads with a single inductor, leading to issues like crosstalk, inefficiency, and thermal runaway due to voltage variations and peak-to-average current errors, especially when using current mode control.
Innovation Solution
A control module that uses pulse width modulation to selectively supply power to the load with the largest error voltage during each cycle, employing a single inductor to drive multiple LED strings, thereby minimizing cross-talk and optimizing efficiency by maintaining constant current delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single switching power supply uses current mode control to drive multiple LED loads, then the design is simplified and board space is saved, but voltage variations cause thermal runaway and peak-to-average current errors
Solution Approach 1:
The patent divides the control of multiple LED loads into separate control loops, with each LED string having its own error voltage signal generated by a dedicated amplifier. This segmentation allows independent regulation of each load despite sharing a common inductor, preventing thermal runaway while maintaining the single power supply architecture.
Solution Approach 2:
The patent implements feedback control by generating error voltage signals from the output voltages of each LED string and feeding them back to the control module. The control module compares these error signals and adjusts the PWM duty cycle accordingly, ensuring stable operation even under varying conditions and preventing peak-to-average current errors.
2Reliability
If voltage is increased to compensate for LED manufacturing variations, then all LED strings operate reliably, but power is wasted due to excessive voltage
Solution Approach 1:
The patent applies local quality control by generating separate error voltage signals for each LED string based on its specific output voltage. Each string receives tailored control according to its actual conditions rather than being forced to operate at a uniform high voltage, enabling both reliable operation and energy efficiency.
Solution Approach 2:
The patent dynamically adjusts the PWM duty cycle parameter based on the error voltage signals from each LED string. By changing the duty cycle rather than relying on fixed high voltage, the system maintains reliable operation while minimizing power waste, adapting to individual string characteristics in real-time.
3Area of stationary object
If a single inductor drives multiple LED strings, then board space and cost are reduced, but crosstalk and inefficiency occur
Solution Approach 1:
The patent segments the control function across multiple LED strings by generating separate error voltage signals for each string. This allows the single inductor to be efficiently shared among multiple loads with independent control, preventing crosstalk and improving conversion efficiency while maintaining compact design.
Solution Approach 2:
The patent introduces dynamic control through PWM modulation, where the duty cycle is adjusted in real-time based on the error voltage signals. This dynamic operation allows the single inductor to adaptively serve multiple LED strings with different power requirements, eliminating inefficiency and crosstalk while preserving space savings.
4Device complexity
If peak inductor current is sensed and controlled, then the control loop is simple, but noise immunity is poor and slope compensation is required
Solution Approach 1:
The patent introduces an intermediary approach by using error voltage signals as mediators between the LED string outputs and the control module. Instead of directly sensing peak inductor current, the system uses these intermediate voltage signals to convey information about each LED string's state, improving noise immunity while maintaining control simplicity.
Solution Approach 2:
The patent substitutes the mechanical/current-based sensing approach with an electrical voltage-based control mechanism. By replacing direct current sensing with voltage signal generation and processing, the system achieves better noise immunity and eliminates the need for slope compensation, maintaining simple control loop structure.
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 light output variations and extends LED lifetime by ensuring constant current supply, while minimizing inefficiencies and thermal issues associated with voltage variations, and allows for independent control of each LED string.
Implementation Method 1
a control module configured to supply current from a pulse width modulation output configured to drive a plurality of loads
Implementation Method 2
employing a single inductor to drive multiple LED strings
Data Source
AI summary
Systems and methods of driving multiple outputs are provided in which a single inductor may be used to drive multiple output such as independent strings of LEDs or white LEDs (WLEDs). In an example embodiment, a boost DC to DC converter may be used with a single inductor to drive multiple outputs. In an example embodiment, the error voltage of each of the multiple outputs is sampled during each cycle of the DC to DC converter and the largest error voltage is determined for that cycle. Power from the DC to DC converter is then supplied to that output during that cycle.