A Comparative Study of GaN-Based Direct Current and Alternating Current High Voltage Light-Emitting Diodes

In this work, one type of direct current high voltage light-emitting diode (DC-HV LED) and six types of alternating current high voltage LEDs (AC-HV LEDs) are demonstrated. Comparative current-voltage (I-V) and light output power (LOP)-current (L-I) characteristics are performed between 24V DC-HV LED and 24V AC-HV LEDs with eight working cells. The AC-HV LED has relatively larger wall-plug efficiency (WPE) than DC-HV LED over a current density range from 0 to 152Acm(-2). The effect of the layouts on the optical and electrical properties of AC-HV LEDs is further investigated. Owing to larger heat dissipation area and fewer number of chips, our combined numerical and experimental results demonstrate that the AC-HV LED I has a more favorable current spreading uniformity compared to other AC-HV LEDs. In addition, it is found that the LOP of AC-HV LEDs is dependent on both the number of working cells and the ratio of radiation area to total chip area. Larger ratio of light emission area to total chip area can be obtained by decreasing the area of rectifier cells. Therefore, in order to achieve a much higher LOP, AC-HV LEDs have to be designed with smaller area of rectifier cells and with more working cells simultaneously.