LED Driver Circuit Synchronizes Switches to Reduce Flicker
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Solution Overview
Problem
LED drivers face challenges in maintaining consistent light intensity during discontinuous operation modes, often resulting in flicker, particularly in applications like digital micromirror devices used in varying lighting conditions such as automobile head-up displays.
Innovation Solution
A circuit design that includes a switch control circuit and comparators to generate control signals for switches coupled in parallel with the LED, using a current loop and inductor to maintain a stable loop current, ensuring consistent light intensity by synchronizing the switching of switches SW1 and SW2, thereby avoiding flicker.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the LED is operated in discontinuous mode to reduce power consumption, then energy efficiency is improved, but light intensity consistency deteriorates causing flicker
Solution Approach 1:
The patent implements a feedback mechanism where the actual loop current is continuously monitored and compared with a reference current. The error signal generated drives the control circuit to adjust the switch timing, ensuring that the LED receives consistent current pulses each cycle. This closed-loop control eliminates flicker while maintaining discontinuous operation for energy savings.
Solution Approach 2:
The patent dynamically adjusts the switch on-time and off-time based on real-time current measurements. The control circuit modifies the switching parameters continuously to maintain optimal current delivery to the LED, ensuring consistent light output despite the discontinuous operation mode.
2Illumination intensity
If the switch on-time is increased to maintain consistent light intensity, then illumination consistency is improved, but the frequency of switching decreases affecting response speed
Solution Approach 1:
The patent applies partial action by using precise, optimized switching durations that are just sufficient to deliver the required current. The control circuit calculates the minimum necessary on-time to achieve consistent light output, avoiding excessive switching time while maintaining intensity consistency. This optimized approach preserves response speed.
3Illumination intensity
If the loop current is increased to compensate for LED efficiency variations, then light intensity consistency is improved, but power consumption increases
Solution Approach 1:
The patent changes the control parameter from fixed current delivery to dynamic current regulation based on actual LED performance. The control circuit adjusts the loop current in real-time according to measured LED characteristics, delivering only the necessary current to achieve consistent light output. This adaptive parameter adjustment prevents unnecessary power consumption while maintaining intensity consistency.
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
The solution ensures consistent light intensity levels each time the LED is activated, reducing flicker and adapting to different lighting conditions by maintaining a stable loop current through the LED, enhancing the performance of LED drivers in discontinuous operation modes.
Implementation Method 1
A first switch SW1 is coupled in parallel with an LED D1. A second switch SW2 is coupled to the first switch SW1 via an inductor L1
Implementation Method 2
A first comparator COMP1 has first and second inputs and an output. The first input is coupled to a photo-sensitive device D2
Data Source
AI summary
In described examples, a circuit for controlling a light emitting diode (LED) includes a switch control circuit to generate a first control signal for a first switch coupled in parallel with the LED. The switch control circuit generates the first control signal responsive to a magnitude of loop current through the first switch relative to a first reference signal. A switch driver generates a second control signal for a second switch coupled to the first switch via an inductor. The first switch driver generates the second control signal responsive to the magnitude of the loop current through the first switch relative to the first reference signal.