Increasing luminous efficiency of led by joint dimming mode with adjustable peak current

Abstract

Luminous efficiency and color temperature of LED chip are affected by current and temperature. PWM dimming mode only works at two kinds of current levels-rated current and zero current. It has smaller effect on color temperature compared with linear dimming mode, but it will reduce the luminous efficiency of lamps. Linear dimming mode has higher luminous efficiency by comparison. The two dimming modes above cannot keep color temperature stable and Luminous efficiency high. Therefore, the paper designed a joint dimming mode by integrating advantages of the two modes. The dimming method not only adjusts peak current, but also changes the duty cycle of dimming signals. The injected average current is kept stable by reducing peak current and increasing the duty cycle. The decreased luminous efficiency by the raise of temperature was made up for. Then according to the mathematical model of total flux and current, the author calculates the mathematical mode of flux affected by temperature. It proves the fact that adjusting peak current slightly can compensates for the reduced luminous efficiency affected by temperature through theoretical calculation. In addition, the final peak current after calculation can contribute to the adjustment parameter of joint dimming modes.