Adaptive Digital Ramp Current Control for LED Drivers
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The use of square wave signals to drive LEDs in contact image sensors leads to undesirable effects such as radiated emissions and ground bounce, causing radio frequency interference and voltage fluctuations on circuit boards, which affect the operation of other components.
Innovation Solution
An adaptive digital ramp current control system that digitally ramps up and down the current supplied to LEDs, using a predetermined or dynamically modified ramp profile to control the switching characteristics, reducing RF emissions and ground bounce by adjusting the rate and duration of current changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a square wave signal is used to drive the LED, then the LED can be simply controlled with high and low voltage states, but radiated emissions and ground bounce occur causing RFI and voltage fluctuations
Solution Approach 1:
The patent segments the square wave current into multiple discrete current levels (first current level, second current level, third current level) during the LED on-period. Instead of abrupt transitions between high and low states, the current transitions through intermediate levels, which reduces the harmful electromagnetic effects while maintaining control functionality.
Solution Approach 2:
The patent dynamically adjusts the current levels and transition timing based on the LED drive cycle. The controller selectively applies different current levels at different times within the on-period, and adjusts the ramp-up and ramp-down rates to optimize both the LED performance and the reduction of radiated emissions and ground bounce.
2Speed
If the current is rapidly switched to achieve fast LED response, then the LED responds quickly to control signals, but ground bounce and RFI increase
Solution Approach 1:
The patent implements periodic current transitions with controlled ramp-up and ramp-down rates. Instead of instantaneous switching, the current transitions through defined time intervals at each level, creating a periodic pattern that maintains response speed while distributing the transition energy to reduce ground bounce and RFI.
Solution Approach 2:
The patent changes the current transition parameters by introducing intermediate current levels and controlling the time duration at each level. The ramp-up and ramp-down rates are adjusted as key parameters to achieve fast LED response without causing excessive ground bounce or radiated emissions.
3Illumination intensity
If high current levels are used to increase LED light output, then more light is produced for better illumination, but radiated emissions and ground bounce effects worsen
Solution Approach 1:
The patent segments the high current level into multiple discrete current levels (first, second, and third current levels) during the LED on-period. This allows the system to achieve high illumination output while distributing the current stress over time and reducing the peak electromagnetic transients that cause RFI and ground bounce.
Solution Approach 2:
The patent dynamically transitions between different current levels during the LED on-period rather than maintaining a constant high current. The controller adjusts the timing and duration of each current level to maintain adequate light output while minimizing the harmful electromagnetic effects associated with high current switching.
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
Substantially reduces and eliminates undesirable RF emissions and ground bounce effects, improving the operational stability and efficiency of contact image sensors by tailoring the current switching behavior.
Implementation Method 1
Light emitting diodes (LEDs) are often driven with a square wave signal
Implementation Method 2
The intensity of the light from the LED is dependent on the duty cycle and current level
Data Source
AI summary
An adaptive digital ramp current control system comprises a digital current ramp controller configured to digitally ramp a current level supplied to at least one light emitting diode (LED) according to a predetermined ramp profile, the ramp profile comprising at least one intermediate current level step between a minimum current level and a maximum current level.