Backlight Drive Circuit Voltage Drop Compensation
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Solution Overview
Problem
In vehicles with idle-stop technology, the temporary reduction in battery supply voltage during engine cranking causes instability in the operation of in-vehicle liquid crystal displays, leading to potential shutdowns due to excessive current draw by the backlight, which is not adequately addressed by existing drive control methods.
Innovation Solution
A display apparatus with detection means to identify voltage drops, adjusting the drive current and duty cycle of the backlight to reduce power consumption, using variable resistance and PWM control to maintain operation within a guaranteed voltage range and compensate for luminance reductions, while also correcting image data luminance and gamma values as needed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the drive circuit maintains constant current output to the backlight, then the luminance and chromaticity stability is improved, but the supply voltage drops further when cranking is performed
Solution Approach 1:
The drive circuit dynamically adjusts its operating parameters based on the supply voltage level. When cranking is detected or supply voltage drops below a threshold, the circuit transitions from constant current mode to a mode that limits current consumption, thereby adapting to changing voltage conditions and preventing excessive voltage drops.
Solution Approach 2:
The drive circuit changes its current output parameters in response to supply voltage variations. By monitoring the supply voltage and adjusting the drive current accordingly, the circuit maintains stable backlight performance during normal operation while reducing current draw during voltage drops to prevent shutdown.
2Illumination intensity
If the drive circuit draws large current to maintain backlight luminance, then the display brightness is improved, but the supply voltage drops below the guaranteed operating voltage
Solution Approach 1:
The drive circuit incorporates feedback mechanisms to monitor supply voltage levels and adjust backlight current accordingly. When voltage drops are detected, the circuit reduces current output to prevent the voltage from falling below the guaranteed operating threshold, thereby maintaining reliable operation.
Solution Approach 2:
The system performs preliminary detection of cranking conditions or voltage drops and takes preventive action by reducing backlight current before the voltage drops below the guaranteed operating level, thus avoiding display shutdown.
3Use of energy by moving object
If the supply voltage is reduced during cranking, then the power consumption is reduced, but the display operation becomes unstable
Solution Approach 1:
The drive circuit dynamically adapts its operation to match supply voltage conditions. During voltage drops, it transitions to a low-current mode that consumes less power, while maintaining sufficient backlight output through extended duty cycle to preserve display stability.
Solution Approach 2:
The drive circuit uses PWM (pulse width modulation) to control backlight output, adjusting the duty cycle periodically. During voltage drops, it increases the duty cycle to compensate for reduced current, maintaining average luminance and display stability despite lower instantaneous power consumption.
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 extends the guaranteed operating voltage range of the display and minimizes noticeable luminance reductions by synchronizing current and duty cycle adjustments with voltage fluctuations, ensuring stable display operation even during battery voltage drops.
Implementation Method 1
detection means for detecting whether a supply voltage from the battery is less than or equal to a threshold value
Implementation Method 2
variable resistance unit that can change a resistance value
Implementation Method 3
the drive circuit 522 determines a time period for which the LEDs 502 are on or off in accordance with the duty cycle contained in the PWM signal
Implementation Method 4
light emitting devices, such as light-emitting diodes (LEDs), are typically used as a backlight source
Implementation Method 5
As for light emitting devices, such as the LEDs 502 constituting the backlight 500, because luminance and chromaticity are determined by a drive current
Data Source
Figure 1
Figure 2
Figure 3~4B
AI summary
A drive control circuit (200) of a backlight (220) includes a drive circuit (240) that drives the backlight (220), a voltage detection unit (250) that detects whether or not a supply voltage Vp from a battery (210) is less than or equal to a threshold value, and a controller (260) that controls the operation of the drive circuit (240). When the supply voltage Vp from the battery (210) is less than or equal to the threshold value, the drive circuit (240) changes a drive current to be supplied to the backlight (220) to a low current value. Furthermore, in response to a change in the drive current, the controller (260) provides, to the drive circuit (240), a PWM signal to extend a time period for which the backlight (220) are on.