Multi-Channel LED Driver with Phase-Divided PWM Bus Voltage Control
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Solution Overview
Problem
Existing LED driver systems face inefficiencies due to slow transient response and high power dissipation caused by manufacturing variations in LED forward voltage drops, leading to longer minimum LED on time and reduced system efficiency, especially in dynamic LCD backlighting applications.
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, allowing the LED bus voltage to be adaptively regulated during the tracking phase and set to a preset value during the pre-charging phase, ensuring high efficiency and fast transient response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single power converter is combined with multiple linear current sinks in a parallel architecture, then device complexity is reduced by eliminating dedicated switching circuitry and passive components for each channel, but transient response becomes slow due to slewing inductor current, charging capacitor voltage, and limited switching frequency
Solution Approach 1:
The PWM dimming cycle is segmented into two distinct phases: a first phase where the LED bus voltage is regulated to a minimum value required to maintain all active LED channels in regulation, and a second phase where the LED bus voltage is pre-charged to a higher value. This temporal segmentation allows the system to optimize for both efficiency and fast transient response without requiring complex per-channel switching circuitry.
Solution Approach 2:
The patent applies preliminary action by pre-charging the LED bus voltage to a higher value during the second phase of the PWM cycle, before the next dimming transition occurs. This pre-charging action ensures that when channels need to be activated, the voltage is already at the required level, eliminating slow transient response while maintaining the simple parallel architecture.
2Reliability
If the LED bus voltage is regulated to a preset constant value, then all active LED channels are maintained in regulation, but power dissipation increases and system efficiency decreases
Solution Approach 1:
The patent implements dynamic voltage regulation by adjusting the LED bus voltage based on the actual needs of active channels. During the first phase, the voltage is regulated to the minimum value required to maintain active channels in regulation. During the second phase, the voltage is pre-charged to a higher value. This dynamic approach reduces power dissipation compared to constant high-voltage regulation while ensuring reliable channel operation.
Solution Approach 2:
The system changes the LED bus voltage parameter over time within each PWM cycle. The voltage transitions from a minimum regulation level during the first phase to a pre-charged higher level during the second phase. This parameter change allows the system to maintain channel regulation with minimal power dissipation while preparing for fast transient response.
Data Source
AI summary
System and method for a light emitting diode (LED) driver are disclosed. To supply an LED bus voltage to a large array of LEDs organized in multiple channels where one or more LEDs are connected in series in each channel, an LED driver includes a power converter, a feedback generation circuit, and a phase-division based controller. The power converter is configured for providing the LED bus voltage to the multiple LED channels based on a voltage control signal. The feedback generation circuit is configured for generating a feedback signal based on the LED bus voltage supplied to the multiple LED channels. The phase-division based controller is configured for generating the voltage control signal based on the feedback signal and information from the multiple LED channels. The phase-division based controller divides each pulse width modulation (PWM) of each channel into a tracking phase and a pre-charging phase so that the LED bus voltage supplied to the multiple channels changes between the tracking phase and the pre-charging phase.