LED Backlight Driving Apparatus PWM Dimming Control
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Solution Overview
Problem
Conventional LED backlight modules require external capacitors for dimming signal processing, which limits frequency flexibility and accuracy in adjusting brightness, especially when using pulse width modulation (PWM) dimming signals.
Innovation Solution
An LED driving apparatus that converts PWM dimming signals into analog voltage signals without external capacitors, utilizing a sensing resistor, adjustable voltage-divider circuit, comparator, power converter, and control circuit to accurately adjust brightness by generating a reference voltage representing the dimming signal's duty cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If external capacitors are used to filter the dimming signal to generate an analog voltage signal, then the brightness adjustment can be achieved, but the device complexity increases and the frequency flexibility is limited
Solution Approach 1:
The patent extracts the signal processing function from external passive components (capacitors and resistors) and relocates it to an integrated control circuit. The control circuit directly processes the PWM dimming signal and generates the analog voltage signal without requiring external filtering components, thereby reducing device complexity while maintaining brightness adjustment capability.
Solution Approach 2:
The control circuit is designed to perform multiple functions: it directly processes the PWM dimming signal, generates the analog voltage signal for LED string control, and eliminates the need for separate external filtering components. This multi-functional integration reduces the overall component count and simplifies the circuit structure.
2Adaptability or versatility
If the dimming signal frequency is reduced to achieve lower brightness adjustment frequencies, then the brightness control range is improved, but the filtered analog voltage signal becomes distorted and measurement precision deteriorates
Solution Approach 1:
The patent replaces the passive RC filtering mechanism with an active control circuit that directly processes the PWM signal. Instead of relying on RC time constants that limit frequency response, the control circuit uses active signal processing to accurately convert PWM signals across a wide frequency range into precise analog voltage signals, eliminating signal distortion.
3Ease of operation
If additional pins are provided for connecting external capacitors and resistors, then the dimming function can be implemented, but the ease of operation is reduced due to complex external connections
Solution Approach 1:
The patent merges the signal processing function into the control circuit, combining what were previously separate external components (capacitors and resistors) with the main control logic. This integration eliminates the need for additional external connection pins and simplifies the overall system architecture.
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 accurate brightness adjustment of LED strings at any frequency without external capacitors, ensuring precise control over image frame brightness through the duty cycle of the dimming signal.
Implementation Method 1
A first terminal of the sensing resistor is coupled to a cathode of the at least one LED string to generate a feedback voltage
Implementation Method 2
The adjustable voltage-divider circuit is configured to generate a reference voltage according to a dividing ratio, wherein the dividing ratio of the adjustable voltage-divider circuit is controlled by a first signal set and a second signal set
Implementation Method 3
A first input terminal of the comparator is coupled to the first terminal of the sensing resistor to receive the feedback voltage, a second input terminal of the comparator is coupled to the adjustable voltage-divider circuit to receive the reference voltage, and an output terminal of the comparator is configured to generate a control signal
Implementation Method 4
The power converter is coupled between the output terminal of the comparator and an anode of the at least one LED string and configured to provide a DC voltage to the anode of the at least one LED string according to the control signal
Implementation Method 5
The LED backlight module has a plurality of LED strings arranged in parallel, and each of the LED strings is composed of a plurality of LEDs connected in series
Data Source
AI summary
A LED backlight module including a LED string and a driving apparatus is provided. The driving apparatus comprises a sensing resistor, an adjustable voltage-divider circuit, a comparator, a power converter and a control circuit. The sensing resistor is coupled between a cathode of the LED string and a ground potential and generates a feedback voltage. The adjustable voltage-divider circuit generates a reference voltage according to a dividing ratio which is controlled by a first signal set and a second signal set. The comparator compares the feedback voltage and the reference voltage, and generates a control signal accordingly. The power converter provides a DC voltage to an anode of the LED string according to the control signal. The control circuit counts a disable period of a dimming signal to generate the first signal set, and counts an enable period of the dimming signal to generate the second signal set.