Popular mobile phone LCD backlight drive tends to use LDO

[San Francisco] mobile phone backlight color LCD screen using 2 -8 LED light, most of them driven by parallel or single constant current power supply mode. Since 2000, the mobile phone color LCD screen commonly used LED driver has DC/DC switching regulator, charge pump, constant current source and low dropout voltage regulator (LDO).

DC/DC switching regulator is used to store the power inductor, the inductor and easy to launch the switching frequency, prone to new interference on the radio, so in the mobile phone products in less.

Charge pump is a switching regulator, but it is the energy storage electric capacitor, and thus will not launch the switching frequency, accounted for the largest share of the mobile phone products.

LED lighting requirements IF constant current, constant current source is the market for this special design and production, the constant current source is the price of the charge pump 50%, so in recent years the popularity of mobile phone products also occupy a certain share.

LDO is a very good performance of the low dropout voltage regulator, output voltage stability, when the load is constant, its current flowing through the load is constant, the principle based on LDO is a good LED driver.

LDO in voltage - current mode, the use of uniform flow resistance to obtain approximate matching white LED brightness, as long as can be a positive voltage LED changes automatically adjust the bias voltage can be matching requirements for LED to improve the mass production, increase the tolerance degree. LDO rated output current is larger, while the LCD backlight driver only use the output capacity of the 1/5-1/3, more redundancy, the chip is not easy to heat, without too much consideration of heat dissipation. Therefore, the use of 300mA-500mA LDO to do the popular mobile phone LCD backlight driver is a low-cost design choices.

Present mobile phone with LED driver IC market price, a DC/DC switching regulator is priced at $-0.15 $0.12, a charge pump is priced at $-0.25 $0.18, a constant current source is priced at $-0.12 $0.09, and a LDO price of only a few cents. To reduce the cost of mobile phone backlight drive unit, LDO is indeed attractive, in recent years, many popular mobile phones have been selected.

From charge pump, constant current source, low dropout regulator performance / price comparison, charge pump, constant current source, LDO backlight using the actual effect difference. Charge pump, constant current source, LDO use efficiency gap in theory, but in the lithium battery voltage VLI is 3.0V ~ 4.2V, the actual efficiency is similar. In addition, the use of LDO lower power consumption, its cost is also low.

Source: CCID - China Electronics News