LED Driving Device PWM Compensation Forward Voltage
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Solution Overview
Problem
Existing LED display devices face challenges in accurately controlling the ON period of PWM signals to match gray scale values, leading to inefficiencies in light emission and brightness, especially when dealing with large sizes and varying panel characteristics.
Innovation Solution
An LED driving device is introduced, comprising a driving current source, a driving control circuit, a measurement circuit, and a PWM compensating circuit, which senses the forward voltage of LEDs and adjusts the PWM signal to ensure accurate brightness matching by extending the ON period based on the forward voltage reaching time, without requiring a separate sequence or memory.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the driving current is supplied during the ON period of the PWM signal based on gray scale value, then the PWM signal timing is simple and easy to control, but the actual brightness of the LED does not reach the gray scale value because the LED does not emit light immediately when current is supplied
Solution Approach 1:
The patent applies preliminary action by measuring the forward voltage reaching time of the LED before the PWM signal is applied. The measurement circuit detects how long it takes for the LED's forward voltage to reach the comparison voltage, and this measured time is used to pre-compensate the PWM signal's ON period, ensuring the LED has sufficient time to reach the desired brightness level before the PWM timing begins
Solution Approach 2:
The patent implements feedback by using the measurement circuit to continuously monitor the forward voltage reaching time and adjusting the PWM signal accordingly. The measured forward voltage reaching time feeds back to the PWM signal generation circuit, which dynamically adjusts the ON period to compensate for variations in LED characteristics, ensuring accurate brightness control
2Measurement precision
If a separate measurement sequence is used to measure forward voltage reaching time, then the measurement accuracy is high, but the device complexity increases and additional sequences are required
Solution Approach 1:
The patent merges the forward voltage reaching time measurement function with the existing PWM signal generation and control circuits. The measurement circuit uses the same comparison voltage generation mechanism already present in the PWM control system, eliminating the need for separate measurement sequences or additional complex control logic while maintaining high measurement accuracy
3Device complexity
If the PWM signal is not compensated for forward voltage reaching time, then the circuit is simple, but there is loss in gray scale value and inaccurate brightness control
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the PWM signal's ON period parameter based on the measured forward voltage reaching time. The compensation amount is calculated by changing the ON period parameter to account for the time delay, ensuring that the LED brightness accurately matches the intended gray scale value without requiring complex circuit modifications
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
This solution allows for precise control of LED brightness to match gray scale values, compensates for forward voltage reaching times, and measures forward voltage reaching times accurately, ensuring consistent performance across different panel characteristics using a simple circuit configuration.
Implementation Method 1
a measurement circuit configured to sense a one-side voltage of the LED, and output a comparison voltage corresponding to a forward voltage of the LED and the one-side voltage
Implementation Method 2
during a scan time for the LED, change a state of a first element during a time in which the one-side voltage reaches the comparison voltage, and compensate for the PWM signal depending on a time during which a state of a second element is changed to correspond to that of the first element
Data Source
AI summary
An embodiment relates to an LED driving technique. The embodiment provides a technique of measuring a forward voltage reaching time of a currently driven LED by comparing a forward voltage sensed in a previous scan line and an LED voltage sensed in a current scan line, and compensating an ON period of a pulse width modulation (PWM) signal by the measured forward voltage reaching time.