In portable devices, the keyboard or touch screen, when used in the LED current when the highest, and in a few seconds without action, to reduce power consumption will reduce the LED current, the LED current control is a common approach is to use PWM pulses to drive the chip enable, through startup and shutdown the chip, the output current is the average of the PWM signal duty cycle. For new LED driver chips, the use of a single (S-Wire) or two wire I2C interface, so just use one or two I / O ports, and thus the design is very simple. the highest efficiency of over 93%, while the average efficiency of approximately 80%. |
Progressive changes in brightness are mainly used in portable devices Startup or Shutdown to create theatrical lighting effects, at boot time, equally at shutdown gradually reduce the reverse movement, with the help of the microprocessor can be with different frequency of the PWM signal to the LED drive circuit is enabled client to achieve such effects, the LED current specific time intervals a stepped manner with multiple increased or decreased, but the disadvantage of this method is time-consuming processor resources, NCP5602 and NCP5612 such products on the LED driver chips have this feature.
If applied to RGB LED on when such a function can be used to generate situational lighting effects, laptop battery has a 32 per RGB LED brightness, such as the NCP5623 LED driver chips can be staggering 32,768 colors changes due to such a fine brightness level difference and is embedded in a logarithmic algorithm of color changes linearly and relatively supple, RGB LED driving circuit includes three LED to adjust the output current of the current source independent PWM control to produce the desired color output. the backlight current laptop battery will be pre-set time intervals in a stepwise manner gradually enlarged to 20mA.
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