Applying Hybrid Passive Current-Sharing Components to Non-Isolated LED Driver

Abstract

The capacitive current balancing LED driver based on the boost converter features simple structure and high-precision LED current balance. However, when the number of the LED strings is increased, the output voltage will also increase because the output voltage is the sum of total LED string voltages. Consequently, the duty cycle will increase to achieve the requirement of a high output voltage. In this paper, an improved non-isolated single-switch four-channel LED driver with automatic current balance is presented. Although there are four LED strings, the output voltage is only the sum of two LED strings. Thus, more LED strings can be used. In the proposed LED driver, the currents flowing through the LED string 1 and LED string 2 are balanced by one current sharing capacitor, and the currents flowing through the LED string 3 and LED string 4 are balanced by the other current sharing capacitor. Owing to the manufacturing deviation of LEDs and different trace impedance, the sum of the currents in LED string 1 and LED string 2 are not equal to the sum of the currents in LED string 3 and LED string 4. Therefore, a differential-mode transformer is connected between the two current sharing capacitors to balance the four LED currents. Since each winding of the differential-mode transformer is connected in series with a current sharing capacitor, the leakage inductors of the differential-mode transformer can limit the current peak. Also, the dc magnetizing inductance current is zero. Thus, no extra demagnetizing circuit is required. Furthermore, only one LED string current is sensed and controlled. Finally, the operating principles, analyses and experimental results are offered to verify the effectiveness of the proposed four-channel LED driver.