LED lighting has become the focus of everyone's attention because of its high energy saving, long life and environmental protection. There have been many successful cases in the field of functional lighting in many parts of the country. China's semiconductor lighting application technology is gradually in the forefront of the world. With the encouragement of national and local government policies, many places are in outdoor lighting such as: street lights, landscape lighting, etc.; indoor lighting such as: subway, underground garage, museum; special occasion lighting : Such as low temperature lighting, miner's lamp lighting, car lights and other aspects are widely used. Some traditional lighting companies have begun investing in transforming LED luminaires. LED indoor lighting and application technology are advancing by leaps and bounds. Indoor lighting is undoubtedly a huge market, and the market prospects are beyond doubt. I believe that in 2010, it will occupy a large market share in home lighting.
The most common lamps for indoor lighting are E220, GU10, PAR30, PAR38 and other AC220V high-voltage direct input LED spotlights. E27, Gu10 LED spotlights need to be directly converted into DC LED constant current source to drive high-brightness LED light source. Integrated circuit products for single SoCs are not currently available, and most are switching power supply solutions with primary or secondary feedback. However, the original feedback scheme has the problem that the output current accuracy is not high, and is generally around +-5%. The flyback constant current drive scheme with secondary feedback provides an output current accuracy of +-2%.
There are many drive ICs for the flyback constant current drive scheme that can be used for secondary feedback. This article will introduce the offline LED spotlight design technology based on the PT4201 control chip.
1W-30W offline high brightness LED driver controller PT4201
The PT4201 is a high-brightness LED driver controller that operates in current mode and can drive 1W to 30W illumination or spotlights. It is suitable for a wide range of LED lighting and spotlight applications from 1W to 30W, including E27, PAR30, PAR38 and more. The high-brightness LED drive system based on PT4201's isolated optocoupler feedback has the advantages of high constant current accuracy, simple peripheral circuits, no flicker and low EMI radiation. The oscillation frequency of the controller under normal operating conditions can be accurately set by an external resistor. At the same time, the front side blanking circuit of PT4201 helps to overcome the voltage glitch at the moment when the external power device is turned on, which can effectively avoid the LED light flicker caused by the malfunction of the controller. Internal integrated current slope compensation improves system stability.
The PT4201 provides comprehensive protection to improve the reliability of LED lighting systems, including cycle-by-cycle overcurrent protection (OCP), VDD overvoltage protection (OVP), and VDD undervoltage protection (UVLO). The OUT output pulse high voltage is embedded in an 18V protected external power MOS. The short circuit protection prevents damage to the system when the LED load is shorted.
The PT4201 is available in a SOT-23-6 package with pinouts as shown in Figure 1.
PT4201 basic function description
The PT4201 integrates a variety of enhancements and provides a low-cost solution for low-power LED lighting drives with its extremely low startup and operating current, multiple protection features.
Startup and UVLO:
The PT4201 is activated by charging a capacitor Chold connected to the Vdd pin via a resistor Rstart connected to the high voltage line. At the beginning of power-on, the voltage on the Chold capacitor is 0, PT4201 is in the off state, and the current flowing from Rstart charges Chold to raise the Vdd voltage. When the Vdd pin voltage reaches the chip startup voltage VDD-ON, PT4201 Start working, after the work, the Vdd current increases, and the auxiliary winding starts to supply power to the chip.
The optimized design of the startup circuit allows the VDD to consume very low current before the PT4201 starts. This allows the larger starting resistor Rstart to be used to improve overall efficiency. For general general-purpose input range applications, a 2Mohm, 1/8W resistor and a 10uF/50V capacitor form a simple and reliable startup circuit (Figure 2).
