LED Driver Circuit High-Frequency PWM Dimming
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Solution Overview
Problem
Conventional light source driving circuits for LEDs experience flickering when dimming, causing issues with image sensors capturing flickering images due to a reduction in switch frequency from 1.6 MHz to 100 Hz-2 KHz.
Innovation Solution
A light source driving device comprising a driving unit, voltage converting unit, detecting unit, and feed-back control unit that processes input signals to maintain a high switch frequency for dimming, using a pulse width modulation signal to generate a feed-back signal that corresponds to the brightness of the light source, thereby preventing flickering in images captured by image sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the driving circuit uses low-frequency square wave dimming signal (100 Hz-2 KHz), then the light dimming function is achieved, but the LED flickers and image sensors capture flickering images
Solution Approach 1:
The patent applies periodic action by using pulse width modulation (PWM) to control the LED switching. The driving circuit generates a high-frequency square wave signal (1.6 MHz) that periodically switches the LED on and off, creating a dimming effect through duty cycle control rather than low-frequency dimming. This high-frequency periodic switching prevents the image sensor from capturing flickering while maintaining the light dimming function.
Solution Approach 2:
The patent changes the switching frequency parameter from low frequency (100 Hz-2 KHz) to high frequency (1.6 MHz). By increasing the switching frequency parameter, the LED dimming is achieved without causing visible flickering to image sensors. The dimensionless parameter (duty cycle) is used to control brightness while maintaining high-frequency switching, thus resolving the contradiction between dimming function and flickering.
2Ease of operation
If the switch frequency is reduced to 100 Hz-2 KHz for dimming control, then the light dimming function is achieved, but the image sensor samples the flickering light
Solution Approach 1:
The patent uses high-frequency periodic switching at 1.6 MHz to control LED dimming. This high-frequency periodic action ensures that the light output changes faster than the image sensor's sampling rate, preventing the sensor from capturing flickering. The periodic PWM signaling maintains precise control over light output while avoiding measurement artifacts.
Solution Approach 2:
The patent changes the switching frequency parameter from 100 Hz-2 KHz to 1.6 MHz, which is significantly higher than the image sensor's sampling frequency. This parameter change ensures that the light dimming control does not interfere with image capture accuracy, as the LED switching occurs too rapidly for the sensor to sample the flickering light.
3Object-affected harmful factors
If high-frequency switching (1.6 MHz) is used to prevent flickering, then image capture quality is maintained, but the light dimming control becomes difficult
Solution Approach 1:
The patent implements feedback control by detecting the actual light output and comparing it with the desired dimming level. The feedback signal is used to adjust the PWM duty cycle, enabling precise dimming control even at high switching frequencies. This feedback mechanism simplifies the control process by automatically compensating for any discrepancies between expected and actual light output.
Solution Approach 2:
The patent replaces traditional mechanical dimming control with electronic pulse width modulation. Instead of using low-frequency analog dimming that causes flickering, the system uses high-frequency digital PWM signaling. This substitution of control mechanism maintains image capture quality while enabling precise dimming control through software-based duty cycle adjustment rather than complex analog control circuits.
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 enables stable light output with high-frequency dimming, preventing flickering in images captured by image sensors, ensuring consistent brightness and reducing flicker-related issues.
Implementation Method 1
The voltage converting unit is coupled to the driving unit and a first end of the light source unit, used to receive the driving signal, and convert the driving signal to a driving voltage
Implementation Method 2
The detecting unit is coupled to a second end of the light source unit, and used to detect an output current of the light source unit, so as to generate a detecting voltage
Implementation Method 3
The feed-back control unit is coupled to the detecting unit and the driving unit, used to receive the detecting voltage and a pulse width modulation signal, so as to generate the feed-back signal according to the detecting voltage and the pulse width modulation signal
Data Source
AI summary
A light source driving device includes a light source unit, a driving unit, a voltage converting unit, a detecting unit, and a feed-back control unit. The driving unit is used to receive an input signal, and convert the input signal to a driving signal for output according to an enable signal and a feed-back signal. The voltage converting unit is used to convert the driving signal to a driving voltage, so as to output the driving voltage to a first end of the light source unit. The detecting unit is coupled to a second end of the light source unit, and used to detect an output current of the light source unit, so as to generate a detecting voltage. The feed-back control unit generates the feed-back signal according to the detecting voltage and a pulse width modulation signal.