LED Drive Circuit With Slope Voltage Correction for PWM Dimming
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Solution Overview
Problem
Existing LED drive devices experience inaccuracies in LED current control due to response delays in PWM dimming, leading to undershoot and overshoot, which degrade current accuracy and reliability, particularly in systems with multiple channels.
Innovation Solution
The implementation of a slope voltage generator with voltage holders and correctors to sample and hold error voltage differences, correcting the slope voltage to maintain precise switching duty, thereby stabilizing LED current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If PWM dimming control is implemented for multiple LED channels, then dimming functionality is achieved, but response delay causes undershoot and overshoot in LED current control
Solution Approach 1:
The patent applies preliminary action by introducing a slope voltage generator that proactively adjusts the slope voltage before the actual LED current deviation occurs. The voltage holders sample and hold error voltage differences in advance, and the corrector preemptively corrects the slope voltage based on predicted current deviations, preventing undershoot and overshoot before they manifest in the LED current.
Solution Approach 2:
The patent implements feedback through the error amplifier that continuously monitors the LED current and compares it with the reference current. The error voltage generated from this comparison is fed back to the slope voltage generator, which adjusts the slope voltage accordingly. This closed-loop feedback mechanism ensures that any current deviation is detected and corrected in real-time.
2Adaptability or versatility
If multiple channels of LEDs are driven simultaneously, then system functionality is enhanced, but current accuracy deteriorates due to response delays
Solution Approach 1:
The patent applies segmentation by providing separate voltage holders and correctors for each LED channel. Each channel has its own error amplifier, voltage holder, and corrector circuit, allowing independent control and correction of current deviations in each channel without interference from other channels. This segmented approach maintains current accuracy in multi-channel systems.
Solution Approach 2:
The patent changes the parameter of slope voltage dynamically for each channel based on its specific current deviations. By adjusting the slope voltage parameter independently for each channel through the corrector circuit, the system can optimize current control for each channel's specific characteristics and operating conditions, maintaining overall system reliability.
Data Source
AI summary
A light emitting element drive device includes: a first voltage holder configured to hold a first difference voltage, which is a difference between an error voltage when a light emitting element is in an off state and a first voltage that is a lowest voltage of a slope voltage; a second voltage holder configured to hold a second difference voltage, which is a difference between the error voltage when the light emitting element is in an on state and the first voltage of the slope voltage; and a corrector configured to correct a voltage difference between the error voltage and the first voltage of the slope voltage based on a difference between the second difference voltage and the first difference voltage.