While the light intensity changes with the PWM dutyĬycle. The LEDs are on, they can be driven at the appropriateĬurrent to give the purest white light (at 15mA or 20mA) Average LEDĬurrent changes with duty cycle by switching betweenįull current and zero current. PWMĬontrolled LED current is shown in Figure 3. In better than a 20:1 dimming ratio without the undesirable blue tint common to white LED backlights. Provides the widest dimming range and the purest white The brightness of the LED can be easily adjusted usingĪ PWM signal, a filtered PWM signal, a logic signal orĪ DC voltage. Modulated (PWM) signal to the R SET pin, the LED current can be adjusted for dimming or brightness control Table 1. By applying an additional DC voltage or a pulse-width The LEDĬurrent is easily programmed over a range of 5mA toĤ0mA by selecting the value of R SET as shown in Tableġ. LED current during shutdown, resulting in less thanġμA of battery current in the standby mode. Noise, high efficiency and matched LED brightness along The constant-frequency step-up topology provides low
LED BRIGHTNESS CONTROL CIRCUIT DRIVER
Li-Ion (or 5V) LED Driver for Four White LEDs. Li-Ion (or 5V) LED Driver for Four White LEDs.įigure 1b. Than 0.65cm 2 of printed circuit board space.įigure 1a. The LT1932 and five external components require less The white LED driver shown in Figure 1 is an ideal solution for Li-Ion powered, 4-LED backlight applications.
LED BRIGHTNESS CONTROL CIRCUIT PORTABLE
Space-conscious portable applications such as cellular Permitting the use of tiny, low profile chip inductorsĪnd capacitors to minimize circuit size and cost in It operates at a constant 1.2MHz switching frequency, The LT1932 comes in the tiny 1mm, ThinSOT ™ package. The internal 36V switch is capable ofĭriving up to eight LEDs in series with 20mA of LED The LED voltage, greatly simplifying the battery/adapter
LED current even when the input voltage is higher than Its unique internal current source accurately regulates Regardless of differences in their forward voltage drops. The LT1932 uses a constant-current step-up architecture that directly regulates the LED currentĪnd guarantees a constant light intensity in each LED, Series should be used to ensure the same illumination Than voltage, a constant-current source driving LEDs in
Since LED brightness is proportional to current rather White LEDs, matching the brightness becomes a majorĭesign consideration for multiple LED applications. However, due to variations in the forward voltage drop of White LEDs are widely used in small LCD backlightĪpplications for simplicity, high reliability and low cost. Design Note 267: High Efficiency White LED Driver Guarantees Matching LED Brightness
0 kommentar(er)
