using different cathode materials

using different cathode materials, new lithium-ion batteries have started to develop. When using this type of battery pack, the design engineer should observe electrical specification limits and adjust the drive circuit. Using the maximum forward voltage of the LED is 3.4V ~ 4V when the input voltage provided by the battery must be equal to or higher than the required drive voltage, and therefore requires a stable current function of the boost converter in series or to promote connected in parallel to the LED. with the use of inductive step-up conversion solution compared to the charge pump drive circuit due to its low cost.

Charge pump converter is widely used on the LCD backlight driver, thin thickness and low noise characteristics and a a better choice, the new IC design has gradually improved the efficiency of the charge pump drive circuit,  Charge pump drive circuit is usually taken 1x and 2x mode of operation, some devices are added to 1.33x and 1.5x mode to improve efficiency in this type of solution, LED connected in parallel, the laptop battery at the same time each LED current is set by separate matching current source, optimum drive circuits on the same chip LED current between any two matching error of about 0.2%.

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%.

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