A Single-Inductor, Multiple-Channel Current-Balancing LED Driver for Display Backlight Applications

Abstract

A single-inductor boost light-emitting diode (LED) driver that can distribute equal dc currents to multiple channels of LEDs is presented. To ensure uniform brightness in display backlight units, the previous approaches used current regulation elements serially inserted in individual LED channels, which incur power losses. Instead, the proposed LED driver adopts a single-inductor-multiple-output boost converter topology, which keeps the channel currents equal in an open-loop fashion by connecting the current-delivering inductor to each channel for an equal period of time, in a time-division multiplexing manner. Furthermore, the sequence of conduction is continuously permutated in order to reduce possible systematic imbalances among the currents. A prototype LED driver demonstrates the peak power efficiency of 93.0% excluding the field-programmable gate array controller power and maximum current balance error of 2.04% while delivering 12.4 W to three channels of high-brightness white LEDs.Index Terms-Current balance error, dc-dc converter, display backlighting, light-emitting diode (LED) driver, single-inductor multiple-output (SIMO).

A novel single-inductor eight-channel light-emitting diode driver for low power display backlight applications

“…Various types of SIMO topology-based boost converters are used to achieve uniform current distribution to all channels [8][9][10][11][12][13]. An extended source-based direct LED display backlighting technique was used to provide uniform current [14].…”

“…This SIMO-based boost converter is designed to work in continuous conduction mode and it supplies the total current to all three channels one by one in one switching period. The SIMO boost converter presented in [8] has a timing diagram as shown in Figure 3. In each switching period of the boost converter, one additional unwanted switching is present in the existing LED driver.…”

“…A guard time of 1.1 µ s is provided before starting the switching sequences of the channels and 1.1 µ s is allocated after completing current distribution to all eight channels. This eliminates the unwanted glitches in the proposed LED driver, whereas in the existing LED driver [8], the current is distributed to consecutive channels by switching OFF transistor S 1 of the first channel and switching ON transistor S 2 of the second channel simultaneously. This simultaneous ON and OFF transition of the control transistors of the channels causes glitches in the existing LED driver, which in turn consumes more power, and the distributed currents will not be uniform.…”

“…The changeover time between the channels in the proposed system avoids simultaneous transitions and hence the unwanted glitches are completely eliminated. The control sequence for the control transistors of the channels were generated by a complex DPWM and digital loop filter [8]. This consumes a large area and enormous dynamic power because of unwanted switching transitions occurring in each cycle.…”

“…The power transistor of the single-inductor eight-channel boost converter is switched at the same frequency [8] to compare the performance metrics of the proposed design. Output lines of the 3-bit binary up-counter are connected to the input terminals of the 3 × 8 decoder.…”