LED Driver Circuit With Segmented PWM For Smooth Low-Light Dimming
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Solution Overview
Problem
LED brightness control using PWM results in stepped changes at low illuminance, causing noticeable flicker and instability, particularly in applications like planetariums where subtle brightness adjustments are crucial.
Innovation Solution
An LED driver circuit with multiple current-limiting circuits and pulse width modulation circuits, where pulse widths are controlled differently for low and high light amount regions, allowing for smoother brightness changes across a wider dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If PWM control is used for LED brightness adjustment, then circuit simplicity is achieved, but stepped brightness changes occur at low illuminance
Solution Approach 1:
The patent divides the LED driver circuit into multiple independent driver circuits, each handling a specific brightness range. The first driver circuit handles high brightness ranges while the second driver circuit handles low brightness ranges. This segmentation allows each circuit to be optimized for its specific range, preventing stepped changes at low illuminance while maintaining overall circuit simplicity.
2Manufacturing precision
If PWM frequency is increased to reduce stepped changes, then brightness control smoothness is improved, but noise increases
Solution Approach 1:
The patent segments the brightness control into multiple driver circuits operating at different PWM frequencies. The second driver circuit handling low brightness ranges operates at a lower frequency that avoids noise generation, while still achieving smooth brightness control through the combination with the first driver circuit. This eliminates the need to increase overall PWM frequency, thus avoiding noise.
3Device complexity
If single driver circuit is used, then device complexity is reduced, but brightness control dynamic range is limited
Solution Approach 1:
The patent divides the overall brightness control into multiple driver circuits, each responsible for specific brightness ranges. This segmentation extends the total dynamic range by combining the capabilities of individual circuits, allowing control from very low to very high brightness levels without requiring a single overly complex driver circuit.
Solution Approach 2:
The patent implements dynamic switching between different driver circuits based on the required brightness level. The control circuit selectively activates appropriate driver circuits depending on whether low or high brightness control is needed, providing adaptability across a wide dynamic range while keeping each individual driver circuit relatively simple.
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
Enables smooth dimming at very low light levels without increasing PWM frequency, reducing noise and flicker, and achieving a higher resolution than traditional PWM systems, effectively addressing the stepped change issue in low illuminance regions.
Implementation Method 1
Since the amount of LED light responds to current in 1 ms or less, which is extremely fast, LEDs have a property in which the brightness and the pulse width are directly proportional to each other.
Data Source
AI summary
An LED driver circuit capable of overcoming the issues in that a brightness change is perceived as a stepped change in a very low light amount region or light abruptly goes out by using PWM control and of realizing smooth dimming even at a very low amount of light is provided. In the LED driver circuit, a first circuit including a first resistor and a first power transistor connected in series and a second circuit including a second resistor and a second power transistor connected in series are connected in parallel with each other and are connected to an LED. First and second PWM signal generator circuits drive the first and second power transistors, respectively. When the first and second power transistors are in an on-state, currents flow through the LED via the first and second resistors, respectively, which enable a smooth brightness change even in a low illuminance region.