Multi-Channel LED Driver PWM Pre-Charging for Fast Transients
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Solution Overview
Problem
Existing LED drivers face challenges in providing a sufficient LED bus voltage during the switching cycle, leading to inefficiencies and longer minimum LED on time due to slow transient response and power dissipation issues, especially with varying forward voltage drops across LEDs.
Innovation Solution
A multi-channel LED driver with a phase-division based controller that divides each PWM dimming cycle into a tracking phase and a pre-charging phase, using a power converter and feedback generation circuit to adaptively regulate the LED bus voltage, ensuring efficient power delivery and minimizing power dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a switching regulator is used to drive multiple LED channels, then high efficiency is achieved, but the transient response becomes slow due to inductor current slewing and capacitor charging
Solution Approach 1:
The patent segments the LED driver into multiple independent current sink channels, each capable of independent PWM modulation. This allows each channel to respond independently to dimming commands without being constrained by a single switching regulator's transient response, effectively solving the contradiction between efficiency and speed.
Solution Approach 2:
The patent implements dynamic LED bus voltage regulation by detecting the minimum forward voltage among all LED channels and adjusting the bus voltage accordingly. This dynamic adjustment optimizes power efficiency while the pre-charging phase ensures fast transient response when LEDs need to turn on, resolving the contradiction between efficiency and speed.
2Loss of energy
If the LED bus voltage is regulated to a constant value, then power efficiency is improved, but the minimum LED on time increases due to slow voltage adjustment
Solution Approach 1:
The patent introduces a pre-charging phase before the normal PWM dimming cycle, during which the LED bus voltage is pre-charged to the required level. This preliminary action ensures that when the LED needs to turn on, the voltage is already ready, minimizing the minimum LED on time while maintaining efficient voltage regulation during the actual dimming operation.
Solution Approach 2:
The patent implements periodic pre-charging cycles synchronized with the PWM dimming cycle. By periodically pre-charging the LED bus voltage at the beginning of each dimming cycle, the system maintains fast transient response capability while spending the majority of time in efficient constant voltage regulation mode.
3Adaptability or versatility
If separate switching circuitry is used for each LED channel, then individual channel control is achieved, but device complexity and cost increase
Solution Approach 1:
The patent merges the power conversion function into a single shared LED bus voltage regulator, while maintaining separate current sink circuits for each LED channel. This combining approach reduces overall circuit complexity and component count compared to having separate switching regulators for each channel, while still preserving individual channel modulation capability through the current sinks.
Solution Approach 2:
The shared LED bus voltage regulator serves multiple functions: it provides power conversion efficiency, establishes a common voltage reference for all channels, and enables individual channel control through the current sinks. This multi-functionality reduces device complexity while maintaining adaptability for individual channel modulation.
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 achieves high system efficiency and fast transient response by optimizing the LED bus voltage regulation, reducing power dissipation and enhancing contrast ratio in dynamic LED applications.
Implementation Method 1
The single power converter, in a form of inductor, capacitor, or transformer based voltage regulator, converts a wide range of input voltage to a single LED bus voltage
Implementation Method 2
high brightness light emitting diodes (LEDs) has led the conventional lighting world into a new era of solid state lighting
Data Source
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AI summary
System and method for a light emitting diode (LED) driver are disclosed. To supply an LED bus voltage (455) to a large array of LEDs organized in multiple channels where one or more LEDs (440,435) are connected in series in each channel, an LED driver includes a power converter (405), a feedback generation circuit (415), and a phase-division based controller (410). The power converter (405) is configured for providing the LED bus voltage (455) to the multiple LED channels based on a voltage control signal (VC). The feedback generation circuit (415) is configured for generating a feedback signal (VFB) based on the LED bus voltage (455) supplied to the multiple LED channels. The phase-division based controller (410) is configured for generating the voltage control signal (VC) based on the feedback signal (VFB) and information (VLED1...VLEDn) from the multiple LED channels. The phase-division based controller (410) divides each pulse width modulation (PWM) of each channel into a tracking phase and a pre-charging phase so that the LED bus voltage (455) supplied to the multiple channels changes between the tracking phase and the pre-charging phase.