High Frequency LED Circuit Dimming Linearity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional LED circuits operating at low frequencies experience noise due to vibration and lose linearity at higher dimming frequencies, resulting in reduced brightness.
Innovation Solution
A high-frequency LED circuit design incorporating an inductor, LEDs, a capacitor, a power MOS, and a switching circuit with a control module, error amplifier, pulse width modulator, and gate driver to maintain linearity and control LED brightness, using a switching signal to manage the power MOS and capacitor charging/discharging for efficient dimming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the operation frequency is increased to reduce vibration noise, then the noise is reduced, but the linearity between LED current and dimming signal is lost resulting in reduced brightness
Solution Approach 1:
The patent employs a feedback mechanism where the actual LED current is sensed and fed back to the control circuit. The control circuit compares the actual current with the desired current based on the dimming signal and adjusts the switching duty cycle accordingly. This closed-loop feedback ensures that the LED current maintains a linear relationship with the dimming signal even at high frequencies above 30 KHz, preventing brightness degradation while operating at noise-reducing frequencies.
2Speed
If the dimming signal frequency is increased above 1 KHz to reduce audible noise, then the vibration noise is reduced, but the linearity relationship between LED current and dimming signal deteriorates
Solution Approach 1:
The patent implements a dynamic control approach where the switching circuit operates at a variable duty cycle within each dimming period. The control circuit dynamically adjusts the on-time and off-time of the switching element based on the instantaneous dimming signal level and feedback from the LED current sensor. This dynamic adjustment maintains precise linearity between the dimming signal and LED current output even when the overall dimming frequency exceeds 1 KHz, thereby preserving manufacturing precision while achieving high-speed operation.
3Manufacturing precision
If conventional LED driver circuits operate at low frequency, then the linearity is maintained, but audible vibration noise is generated
Solution Approach 1:
The patent fundamentally changes the operating parameters of the LED driver circuit by operating the switching element at frequencies above 30 KHz, which is beyond the audible range for humans. Additionally, the circuit employs pulse-width modulation (PWM) with variable duty cycles to maintain precise control over LED current. This parameter change allows the system to achieve both high linearity (through controlled PWM duty cycles and feedback) and elimination of audible noise (through ultrasonic operating frequencies), simultaneously resolving the contradiction between maintaining precision and reducing noise.
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 high-frequency operation without losing linearity, ensuring appropriate brightness and reducing undesirable noise, even at frequencies over 30 KHz, by maintaining efficient charging and discharging processes.
Implementation Method 1
the capacitor is charged when the power MOS is turn on to further turn on the LEDs and the capacitor is discharged when the power MOS is turn off to turn off the LEDs
Implementation Method 2
an error amplifier to generate an error signal according to the dimming signal from the control module
Implementation Method 3
a pulse width modulator to compare the error signal and a reference signal to generate a compare result, the control signal controls the pulse width modulator to turn on when the dimming signal is in the active period and to turn off when the dimming signal is in the inactive period
Data Source
AI summary
A LED circuit comprises: an inductor, a group of LEDs, a capacitor, a power MOS and a switching circuit. The inductor is connected to a voltage supply and a first node; the group of LEDs is connected to the first node and a ground potential; the capacitor is connected to the first node and a ground potential; the power MOS is connected to the first node and a ground potential, wherein the gate of the power MOS receives a switching signal such that the capacitor is charged when the power MOS is turn on to further turn on the LEDs and the capacitor is discharged when the power MOS is turn off to turn off the LEDs. The switching circuit is to generate the switching signal.