Flicker-Free LED Driver with Linear Voltage Regulation
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Solution Overview
Problem
LEDs are sensitive to voltage ripple from single-phase AC power supplies, leading to flickering due to low differential impedance, which affects their performance and causes distortions in images captured under LED lighting, especially when the instantaneous voltage is below the junction voltage, resulting in flickering frequencies that can interfere with image capture devices.
Innovation Solution
A flicker-free LED driving apparatus comprising a power conversion circuit, feedback circuit, and linear voltage-regulating circuit, which includes an AC to DC rectifier, transformer, switching device, and controller to generate a stable output voltage with reduced ripple, using a feedback signal to regulate the voltage and maintain a stable LED string operation, thereby preventing flickering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-phase AC power supply with rectifier circuit is used to power LEDs, then the power supply structure is simple and cost-effective, but voltage ripple causes flickering and image distortion
Solution Approach 1:
A secondary linear voltage-regulating circuit is introduced as an intermediary component between the power conversion circuit and the LED string. This circuit includes a regulating transistor and control circuitry that actively compensates for voltage ripple by adjusting the transistor's conduction state based on feedback from the LED string voltage, thereby eliminating flickering while maintaining the simple single-phase AC power supply structure
Solution Approach 2:
The patent dynamically changes the operating parameters of the voltage-regulating circuit, specifically adjusting the duty cycle of the regulating transistor based on the detected voltage difference between the output voltage and LED string voltage. This parameter adjustment allows the circuit to adapt to varying ripple conditions and maintain stable LED operation
2Loss of energy
If the instantaneous voltage of pulsed DC power supply is below the junction voltage value, then power consumption is reduced, but LEDs turn off causing flickering at 120 Hz
Solution Approach 1:
A feedback circuit is implemented that continuously monitors the voltage across the LED string and compares it with the output voltage from the power conversion circuit. The feedback signal is used to control the regulating transistor, ensuring that sufficient voltage is maintained across the LEDs during the pulsing cycle to prevent turn-off and eliminate flickering, while still allowing for energy-efficient operation
3Power
If voltage ripple is present in the output voltage, then the power conversion efficiency is improved, but significant ripple current is generated in LEDs due to low differential impedance
Solution Approach 1:
The linear voltage-regulating circuit acts as a buffer intermediary between the power conversion circuit and LED string. The regulating transistor absorbs the voltage ripple variations, maintaining a stable voltage across the LEDs and preventing ripple current generation, while the feedback mechanism ensures efficient power transfer by dynamically adjusting the regulating element's operation
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 suppresses flickering in LED lighting systems by regulating the output voltage and maintaining a stable LED string operation, ensuring consistent lighting quality and reducing distortions in images captured under LED illumination.
Implementation Method 1
an AC to DC rectifier, and is arranged between the AC power source and the transformer for converting an AC electricity into an input voltage
Implementation Method 2
a transformer, and includes a primary winding and a secondary winding, wherein the primary winding is electrically connected to the AC to DC rectifier
Data Source
AI summary
A flicker-free LED driving apparatus and voltage regulating method thereof are disclosed. The apparatus includes a power conversion circuit receiving an AC electricity and then generating an output voltage with a ripple component for an LED string; a feedback circuit electrically connected to the power conversion circuit and generating a feedback signal with varying duty cycle according to operation states of the LED string; a power conversion circuit including, a controller receiving the feedback signal turns on or off a switching device thereof according to the feedback signal; and a linear voltage-regulating circuit electrically connected to the power conversion circuit, the feedback circuit, and the LED string. and configured to regulate the output voltage in accordance with a voltage difference between the output voltage and a voltage across the LED string.