LED Driver Controller Regulating Average Current via Peak Feedback
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Solution Overview
Problem
Conventional LED drivers face challenges in maintaining a constant current, leading to potential damage from exceeding maximum voltage ratings, as the current through an LED string is heavily dependent on voltage, and household power sources are typically constant voltage rather than constant current.
Innovation Solution
A converter system comprising a current sensor, a switch, and a controller is used to derive a feedback signal from the peak current through an LED string, allowing the controller to regulate the average current by varying the duty cycle, thereby maintaining a consistent current level regardless of the number of LEDs in the string.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a constant voltage power source is used to drive an LED string, then the circuit is simple and easy to operate, but the current through the LED string becomes unstable and may exceed maximum ratings causing damage
Solution Approach 1:
The patent employs a feedback mechanism where a current sensor monitors the peak current through the LED string and provides feedback to the controller. The controller adjusts the switch duty cycle based on this feedback to maintain constant average current, preventing current excursions that could damage LEDs while keeping the system relatively simple to operate
Solution Approach 2:
The patent changes the control parameter from direct voltage control to duty cycle control of a switching element. By modulating the duty cycle of the switch based on feedback from the current sensor, the system maintains constant average current through the LED string, resolving the contradiction between operational simplicity and reliability
2Illumination intensity
If the number of LEDs in the string is increased to achieve higher illumination, then the total light output increases, but the current becomes more sensitive to voltage changes and harder to regulate
Solution Approach 1:
The feedback loop continuously monitors the peak current regardless of how many LEDs are in series, allowing the controller to adapt to changing total LED forward voltages. This maintains stable current regulation even as the illumination intensity increases by adding more LEDs to the string
Solution Approach 2:
The patent designs a universal LED driver circuit that can accommodate LED strings with varying numbers of LEDs. The feedback-based control system with adjustable duty cycle provides a multi-functional solution that regulates current for different LED string configurations without requiring different circuit designs, thus managing complexity while enabling flexible illumination scaling
Data Source
AI summary
A system and method for providing a constant current source driver for a light emitting diode string. The converter includes a current sensor that derives feedback signal corresponding to a peak current through the light emitting diode string. The feedback signal is used by a controller to vary a duty cycle of the controller to regulate the average current. The controller is operable to regulate the average current as the number of light emitting diodes is increased and/or decreased.