Research On Multi-channel LED Driver Based On Balance Capacitor

Light-emitting diode(LED)has been widely used in various lighting fields due to its significant advantages of high luminous efficiency,long life,small size and environmental friendly characteristics,etc.Because the power of single LED is still small,it is necessary to use multi-channel LEDs which are formed by connecting them in series and parallel to obtain high brightness.Since the voltage-current characteristic of LED is nonlinear,there is a large current deviation among the channels.Therefore,current balancing technique is of great value and significance to ensure the normal operation of LED and realize the uniform illumination.The research on multi-channel LED driver based on balance capacitor in this paper is based on this background.Firstly,this paper systematically summarizes the existing current balancing technique of multi-channel LED.In contrast to the active method,the passive method based on balance capacitor has great advantages in circuit structure,efficiency and cost,which also eliminates the requirement of bulky coupled inductors.Subsequently,combined with the working principle of the balance capacitor,the following three kinds of multi-channel LED driver based on different circuit topologies are proposed according to the electrical characteristics of LED and the commonly used drive modes.1)A multi-channel LED driver based on the single-switch non-isolated topology is proposed.According to the charge balancing principle of capacitor,it can realize the current sharing drive of N-channel LED based on the traditional non-isolated topology,using N-1 balance capacitors.Since it only uses one switch and one inductor,the cost effectiveness is the most powerful advantage of the proposed driver.After analyzing the evolution of the circuit and the current sharing principle,the performance and feasibility of the driver is validated by the simulation and experimental results from a 12 W prototype with three-channel LED.2)A multi-channel LED driver is proposed based on the asymmetric forward-flyback topology.By combining the advantages of the conventional forward converter and flyback converter,the proposed driver based on the charge balancing principle of capacitor not only solves the security problems of non-isolated multi-channel LED driver,but also improves the efficiency due to the soft switching.In addition,this paper studies the application of multi-channel LED current sharing circuit when the value of balance capacitor is small,which overcomes the difficulties of the device selection and the peak current while the switch is ON.The structure and working principle of the circuit are analyzed and verified by software simulation.3)A multi-channel LED driver is proposed on the basic of the resonant topology.Although the mentioned technique based on the charge balancing principle of capacitor can achieves good current sharing effect,it still suffers from the difficulties of the channel expansion and the lack of short or open circuit protection mechanism.Moreover,compared with other non-resonant topology,the resonant topology,especially LLC topology,enjoy several advantages apart from high efficiency and high reliability.This paper studies on the new driver combining with capacitive impedance balancing method and LLC topology,that it modulates the output by changing the resonant frequency based on switch-controlled capacitor,and thus avoids the change of the balance capacitance.The influence of the balance capacitor on the LLC topology is investigated by modeling and analyzing the circuit.Finally,the driver is verified by simulation and experimental prototype.This paper shows that the current balancing technique based on balance capacitor plays a significant role in extending the channels of LED driver,improving the conversion efficiency and reducing overall cost.