Because 3G mobile phones must use color display screens and lighting technologies, such as flip lighting, color indicators, camera flash, auxiliary lighting, and ambient light sensing, it is necessary to use more advanced lighting management solutions to meet lighting requirements. Various requirements.
White LEDs that provide backlighting for mobile phones Currently, almost all cellular phones have one or two color display screens. Although the level of backlight technology they require varies depending on the number of white LEDs required, most mobile phones currently use up to four white LEDs for their main display. In addition, the folding phone has an auxiliary display screen that is driven by one or two backlit white LEDs. Therefore, the total current of all LEDs is between 100mA and 120mA, which accounts for a large part of the overall power consumption of the mobile phone.
Since the typical forward voltage of a white LED (VF=3.2V Ì„4V) is higher than the typical minimum voltage of the battery of 2.8V Ì„3V, the white LED cannot be directly driven by the lithium battery. For this reason, the power supply system needs to add a DC/DC boost converter to increase the battery voltage. This boost converter can be inductive (magnetic boost) or capacitive (charge pump). Which converter is better depends on the maximum load current required, the efficiency level, and the number of external components. And the required noise level, etc.
Currently, white LED backlight drivers are connected in series or in parallel. The serial mode requires a higher output voltage, so a magnetic boost converter is required. LEDs connected in parallel can be driven with supply voltages as low as 4.5 to 5V, and magnetic boost or charge pump can be used to provide the drive voltage. Both types of drive systems can use an external PWM signal to regulate the current of the LED.
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