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.
Highlights
PMW dimming can caused electromagnetic interference frequency, and produced color cast as the temperature rises[18].The paper combined the small effect PMW dimming mode had on color temperature with the advantage of high luminous efficiency of analog dimming, proposing a joint dimming mode based on these two dimming modes
The new mode kept color temperature of the lamps stable, and made luminous efficiency remain at a high level
The circuit is integrated with the LED display module. It displayed the value of the duty cycle facilitating adjusting the effective-average current
Summary
PMW dimming can caused electromagnetic interference frequency, and produced color cast as the temperature rises[18]. The paper combined the small effect PMW dimming mode had on color temperature with the advantage of high luminous efficiency of analog dimming, proposing a joint dimming mode based on these two dimming modes. The new mode kept color temperature of the lamps stable, and made luminous efficiency remain at a high level. By looking up luminous flux and changing trend of current of a lamp in OSRAM Company, the author established a mathematical model related to them, and gave the compensation current through calculating.
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