UL75

Preliminary

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

6 of 7

www.unisonic.com.tw

QW-R125-051.b

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APPLICATION INFORMATION

Application information

UTC UL75 is a linear constant current driver IC for LED lighting, which is applied to the non isolated LED driver

power supply.

The 500V power transistor is integrated with the constant current drive architecture and control method, which only

needs a few external components to achieve excellent constant current characteristics. Piecewise constant current

control mode to achieve higher PF value and efficiency,

Built in soft start mechanism and the line network monitor adjust system output power.

LED open circuit protection、LED short circuit protection、sampling resistance short circuit protection、over

temperature regulation and other protective functions to improve the reliability of the system.

Start

After the system is powered up, the input voltage is charged on the OUT pin through the depleted MOS, and when

the OUT voltage reaches the threshold value, the chip's internal reference circuit begins to work. When the chip is

working normally, the required operating current is still through the supply of internal consumption.

Constant current control

The chip is detected the peak current, and the RSET resistance is connected to the input terminal of the peak

comparator, which is compared with the threshold voltage 1V. When the RSET voltage reaches the threshold, the

LED current is adjusted, and realized the constant current control.

Among them, RSET is set to LED peak current resistance

Peak current comparator also includes a peak over current protection function. The threshold is about 200mA.

Protection function

UTC UL75 built in a variety of protection functions, including LED short-circuit protection, LED open circuit

protection, sampling circuit short-circuit protection, temperature regulation and protection, etc.

Over temperature adjustment function

UTC UL75 has the function of over temperature adjustment, the output current is gradually reduced when the

driving power is over, so that the output power and temperature rise is controlled, the power supply is maintained at

the set value,

In order to improve the reliability of the system, the chip is internally set to adjust the temperature of the 145°C.

PCB design

In the design of PCB, you need to follow the following guidelines:

OUT bypass capacitor is required to close the OUT pin of the chip.

RSET resistor requires close to the RSET pin of the chip

Between RSET and OUT bypass capacitor resistor connected to the copper foil as short as possible

RSET pin increases in the area of copper clad to improve chip cooling.