Abstract
A buck-type light-emitting diode (LED) driver is proposed herein. The proposed LED driver automatically possesses current sharing and high step-down voltage gain. Without complex control, the proposed LED driver, with a single input and multiple outputs, can achieve automatic current sharing of four-channel LED strings, even under the different number of LEDs of each LED string. Furthermore, as compared with the traditional four-phase interleaved buck converter with a single input and a single output having current sharing required, the proposed circuit has the duty cycle up to 0.5, not 0.25, meaning that under the same input voltage the latter has a wider output voltage range than that of the former. Above all, if the proposed circuit with N outputs, then it still has the duty cycle up to 0.5, not one over N as shown traditionally. Moreover, as compared with the current sharing based on the differential-mode transformer, the proposed circuit has no magnetic resetting loop required. In this paper, the operating principles and design considerations of the proposed converter are discussed. Finally, the theoretical analyses and performances of the proposed LED driver are verified by simulation and experiment.
Highlights
With the progress of science and technology and economic development, traditional incandescent lamps and power-saving bulbs have been gradually replaced by light-emitting diodes (LEDs), because LEDs have the advantages of small size, long life, high efficiency of electricity, low pollution and rapid reaction, more in line with the needs of today’s market [1,2]
The proposed LED driver with automatic current balance is displayed in Figure 2, derived from the circuit shown in [17], and constructed by four switches S1, S2, S3 and S4, four diodes D1, D2, D3 and D4, three energy-transferring capacitors C1, C2 and C3, four output inductors L1, L2, L3 and L4, and four output capacitors Co1, Co2, Co3 and Co4
It is assumed that the demagnetization time of the four inductors in the circuit is the same, and its value is D2 Ts and the four output voltages are clamped by the four LED strings so Vo1 = Vo2 = Vo3 = Vo4 = Vo
Summary
With the progress of science and technology and economic development, traditional incandescent lamps and power-saving bulbs have been gradually replaced by light-emitting diodes (LEDs), because LEDs have the advantages of small size, long life, high efficiency of electricity, low pollution and rapid reaction, more in line with the needs of today’s market [1,2]. [16] presents the interleaved buck LED driver with automatic capacitive current balance and a suitable duty cycle needed to improve the step-down voltage gain. In this circuit, the input and output grounds are separated by the switches, restricting converter applications as well as complicating control design. Such a circuit has automatic current balance under the condition that the maximum duty cycle is limited to 0.25.
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