Sequential LED Backlight Driver for Inrush Current Reduction
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Solution Overview
Problem
Conventional LED backlight drivers for information handling system displays face issues with high inrush currents and transients due to simultaneous turning on and off of LEDs, leading to electromagnetic interference and acoustic noise, which are not effectively mitigated by fixed time delays in PWM dimming.
Innovation Solution
A system and method that dynamically adjust the sequencing time delay based on the number of active LED strings, distributing PWM commands evenly across a cycle to minimize ripple current and adapt to changes in operational strings, allowing optimal operation and reduced power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If fixed time delay is used for sequential LED string driving, then inrush currents and transients are reduced, but ripple current varies with duty cycle and number of strings
Solution Approach 1:
The patent implements dynamic adjustment of the time delay between sequential LED string driving based on the detected number of active LED strings. The delay period is calculated as a function of both the PWM duty cycle and the number of active strings, allowing the system to adapt to different operating conditions rather than using a fixed delay value.
Solution Approach 2:
The patent changes the parameters used to determine the time delay from fixed values to dynamic values that depend on the duty cycle and number of active LED strings. The delay is calculated using the formula: delay = (PWM period × duty cycle) / (2 × number of active strings), which adjusts the timing parameters based on real-time operating conditions.
2Device complexity
If all LED strings are driven simultaneously, then brightness control is simple, but high inrush currents cause EMI and acoustic noise
Solution Approach 1:
The patent divides the LED backlight into multiple separate LED strings that are driven sequentially rather than simultaneously. Each LED string is controlled by a separate PWM command issued at different time intervals, segmenting the current draw over time to reduce peak inrush currents and associated EMI and acoustic noise.
Solution Approach 2:
The patent uses periodic PWM commands to drive each LED string in sequence throughout a PWM cycle. The driver controller issues PWM commands to individual LED strings at periodic intervals determined by the calculated time delay, creating a rhythmic, staggered activation pattern that reduces harmful transients.
3Device complexity
If fixed PWM period is used, then timing is simple, but ripple current varies with number of LED strings
Solution Approach 1:
The patent changes the timing parameters from fixed values to dynamic values that are calculated based on the number of active LED strings and the PWM duty cycle. The time delay between sequential string driving is computed as (PWM period × duty cycle) / (2 × number of active strings), ensuring consistent ripple current regardless of the number of strings.
Data Source
AI summary
An information handling system display backlight illuminates an image with plural strings of LEDs driven by a backlight driver integrated circuit with pulse width modulation. A string detection module detects the number of active LED strings and divides the time period by number of active LED strings into an equal number of time delays or shifts so that the backlight driver sequentially turns on an LED string at a predetermined time period. The active number of LED strings is detected by reading a total number of LED strings from a management interface and subtracting from the total number any detected failed LED strings or any LED strings powered down to reduce power consumption.