High-voltage LEDs offer optimum solution for indoor retrofit lamps (MAGAZINE)

High-voltage LEDs offer optimum solution for indoor retrofit lamps (MAGAZINE)

High-voltage (HV) LEDs have a turn-on voltage that is closer to the mains supply than conventional high-current LEDs. This eliminates components, notably the driver, and offers other advantages, as Epistar’s ALEXANDER WANG explains.
 
A high-voltage (HV) LED, as indicated by the name, is a DC-driven LED with a turn-on voltage greater than 20V, which is much higher than the 2-3V turn-on voltage of conventional LEDs. An HV-LED chip is usually constructed from many small LED cells, which are electrically connected in series. Fig. 1a shows a blue HV-LED chip containing fifteen cells connected in series. The operating current is 20 mA, and the total turn-on voltage across all fifteen cells in series is 48V. This blue HV-LED consumes around 1W in full operation. Fig. 1b shows a red HV-LED chip containing ten cells, again connected in series. The forward current is 20 mA and the overall turn-on voltage is 20V, so the power consumption is around 0.4W.
 
A major advantage of HV-LEDs over conventional LEDs is the forward current, which is typically an order of magnitude smaller in the HV-LED. Low current is favored in LED chip designs due to the better current-spreading effect.