LED Backlight Drive Circuit Prevents Blinking via Voltage Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional LED backlight driver circuits in LCDs suffer from blinking due to delayed charge discharge and require high withstand voltage components, leading to instability and potential safety issues.
Innovation Solution
An LED backlight drive circuit with a power source, output capacitor, and controllable switches, along with voltage dividers and comparators for precise voltage control and overvoltage protection, ensures the LED is only conducting at a predetermined voltage, preventing blinking and ensuring safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a discharge resistor is added at the capacitor end to discharge the capacitor, then the capacitor charge problem is solved, but the circuit power is consumed all the time and unnecessary consumption is caused
Solution Approach 1:
The patent uses the LED lightbar itself to discharge the output capacitor through reverse conduction. When the switch turns off, the LED's reverse recovery characteristics allow it to conduct briefly and discharge the capacitor, eliminating the need for a dedicated discharge resistor and avoiding continuous power consumption.
Solution Approach 2:
The LED lightbar serves dual functions: as the backlight light source and as the discharge path for the output capacitor. This multi-functionality eliminates the need for separate discharge components and reduces overall circuit power consumption.
2Object-affected harmful factors
If the ON speed is accelerated so that the eyes cannot judge whether the LED lights are enlightened twice, then the blinking perception is reduced, but the stability of the system loop circuit is affected and the capacitor electrical charges problem is not directly solved
Solution Approach 1:
The patent converts the potentially harmful effect of capacitor charge accumulation into a beneficial discharge mechanism by utilizing the LED's reverse conduction. This naturally dissipates the harmful charges without affecting circuit stability or requiring excessive ON speed acceleration.
3Measurement precision
If high withstand voltage components are used to handle the higher voltage at the power source output terminal, then the voltage collection is accurate, but the difficulty of selecting devices and the cost increase
Solution Approach 1:
The patent segments the high voltage measurement task by using a voltage divider circuit that divides the high voltage into a lower, manageable voltage for the comparator. This allows the use of standard, low-cost components with lower voltage ratings while maintaining measurement accuracy through the divider ratio.
Solution Approach 2:
The voltage divider acts as an intermediary between the high voltage power source output and the low-voltage comparator. It transforms the high voltage signal into a form that can be processed by standard components, reducing both cost and complexity.
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
The solution effectively prevents LED blinking and reduces the required withstand voltage of components, enhancing system stability and safety while maintaining normal brightness.
Implementation Method 1
a first comparator; a cathode of the first comparator is connected to a first reference voltage, an anode of the first comparator is coupled with the output terminal of the power source, and the output terminal of the first comparator is coupled with the control end of the first controllable switch. When the anode voltage of the first comparator exceeds the cathode voltage, the output terminal of the first comparator drives the first controllable switch to be conducted
Implementation Method 2
a first resistor and a second resistor are connected in series between the output terminal and the ground terminal of the power source; the anode of the first comparator is connected between the first resistor and the second resistor. This is a technical scheme of dividing voltage by the resistors. Because the voltage at the output terminal of the power source is higher, if the first comparator directly collects voltage, the higher withstand voltage capability is required by the devices, which increases the difficulty of selecting devices and the cost. After the voltage is divided by the resistors, the voltage collected from the power source end is decreased in equal proportion, and thus the requirement for the withstand voltage capability is reduced
Implementation Method 3
a second comparator; an anode of the second comparator is connected to a second reference voltage, and a cathode of the second comparator is coupled with an output terminal of the power source; the output terminal of the second comparator is coupled with the control end of the first controllable switch; and the second reference voltage is higher than the first reference voltage. When the cathode voltage of the first comparator exceeds the anode voltage, the output terminal of the first comparator drives the first controllable switch to be blocked. This is an overvoltage protection circuit. When the power source end has the excessive output voltage and its anode voltage drop in the second comparator is higher than the second reference voltage, the second comparator outputs the low level to forcibly switch off the first controllable switch and protect the LED from being broken down by a high voltage
Data Source
AI summary
The invention discloses an LED backlight drive circuit, an LCD device and a driving method. The LED backlight drive circuit includes a power source; an output capacitor and an LED lightbar which is connected in series with a first controllable switch are in parallel connection, and then are arranged between the output terminal and the ground terminal of the power source. The LED backlight drive circuit further includes a first comparator; a cathode of the first comparator is connected to a first reference voltage, an anode of the first comparator is coupled with the output terminal of the power source, and the output terminal of the first comparator is coupled with a control end of the first controllable switch; when the anode voltage of the first comparator exceeds the cathode voltage, the output terminal of the first comparator drives the first controllable switch to be conducted. In the invention, the LED lightbar only can be conducted at the predetermined voltage. Thus, the LED will be unable to be lighted even if the electric quantity is stored in the output capacitor; only when the output voltage achieves the predetermined voltage in the complete ON operation, the first controllable switch is able to be conducted, which solves the problem of LED blinking in the ON operation.