Over the years, the demand for the consumer market for mobile or portable devices and other types of electronic systems, and promote the lighting and display of power With the rapid development of and access to a wide range of applications. Lighting and power, its directory is: a single white LED lights camera xenon flash; single white LED backlight driver; OLED and TFT displays; CCFL (cold cathode fluorescent lamp) backlight; RGB LED drive and other. On the occasion of the white LED driver circuit, this article will be lighting solutions in the RGB LED drive CCFL backlight power converter, the technical features of a typical product of the photoflash charger and application of analysis introduced.
1,1 × / 5 × 7-channel charge pump white LED driver completely backlight solution
APS4070 is a used pump white LED driver power to pay, fully backlit, can the Secretary to support the work screen, Vice-screen and keyboard backlight driver. Serial bus interface can easily transfer complex various parts of the current, flexible drive all the LEDs. Data loaded in the register on power, shut off automatically when you save. Chip reset, the registers in the data set the LED drive current. Very low 33μA LSB current in a non-reflective LCD display allows trickle through the LED. The APS4070 door moving between 1 × and 1.5 × mode switch to high efficiency in all load range. Figure 0 (a) multi-ApsS4070 typical application circuit.
1.1 Main features: End a backlight solutions; divided into three groups of longitudinal independent control, respectively, including the four main LED, LED, and a keyboard LED panel; high current drive capability, four workers LED and two from the LED is 31mA Keyboard LED 60mA; built-in 6-bit DAC precision of no current; input voltage range of 2.7V to 5.5V; interface; shutdown mode, data is stored; 1 × and 1.5 × automatic switching mode; low dropout voltage and current sources. typical value of 200mV; very low LSB current 31μA; low-noise constant switching frequency; 1.8MHz switching frequency compatible with the small size of the external device; power saving mode, quiescent current of only 1μA; over-temperature protection; soft start to reduce the input inrush current; small 16-pin 3mmx3mmQFN package.
1.2 Application areas: mobile phones and smart phones, a variety of handheld devices, a variety of white LED backlight applications, digital cameras, digital cameras, handheld computers and personal media players centers on the device. Figure 0 (b) on a smart phone for the APS4070 application diagram.
2, a single white LED driver circuit
2.1 Technical Support
* Series / parallel LED configuration – topology Driver.
Inductive boost converter to provide the necessary high voltage for the LED tandem. Sequence, an LED tunnel lights in series and only need a current regulator and the two connection points.
The charge pump is generally used to drive parallel LEDs, each LED has a fixed current, otherwise each branch needs a current limiting resistor. This is usually determined by the pre-encapsulation of the LED in the color LED display module configuration.