EMI problems of the hottest white LED driver in mo

  • Detail

Consideration of EMI problems in the design of white LED driver

at present, white LED is widely used as the backlight element of the display screen, and the corresponding white LED driven degradable plastic bag is synthesized by adding starch and other methods, which has become an indispensable IC in the design. White LED driver adopts switching power topology, such as inductive boost converter. When the converter switches at high speed, EMI interference will be caused by using inductance, which will bring difficulties to the design of other functional modules. With the increase of LCD screen, the output capacity required by the driver will increase accordingly, and EMI interference will become serious. Therefore, EMI must be taken seriously when designing white LED drivers

the tps61161 boost converter launched by Ti not only provides the driving capacity of 10 LEDs, but also has corresponding design considerations on EMI. Its typical applications are shown in Figure 1

two switching processes are adopted in the design of tps61161 switch, which effectively reduces the radiation intensity of EMI, so as to avoid the impact of the driver on other modules. As shown in the black curve in Figure 2, when tps61161 can achieve load control and turn on the internal MOSFET switch, the drain source voltage VDS of MOSFET changes from high voltage to low voltage close to zero in a very short time, that is, a large voltage change rate dv/dt; And in the early stage of switching on, due to the characteristics of MOSFET, the current change rate through MOSFET switch is also large, that is, di/dt. Considering the effect of dv/dt and di/dt on EMI, at the initial stage of MOSFET startup, slow down the switching voltage change rate dv/dt to reduce EMI intensity, as shown in the red curve in Figure 2

the actual EMI test results of traditional switching technology and secondary switching technology show that the secondary switching technology of tps61161 reduces EMI radiation energy. In the EMI test, tps61161 drives 10 LEDs in series through the battery voltage of 3.7V. Figure 3A shows the white noise in the EMI test environment space, Figure 3B shows the EMI test results of tps61161 using traditional switching, and figure 3C shows the EMI test results of tps61161 using existing secondary switching technology. The test results show that the secondary switch reduces the EMI radiation intensity by 10dB

in addition, tps61161 supports linear dimming technology - by adjusting the conduction current of the LED, changing the intensity of the LED light to verify the compliance of food contact materials. This dimming method effectively avoids EMI interference caused by LED dimming. Such interference often occurs in PWM dimming mode

of course, in the specific application of tps61161 design, no more than 4 pages of good PCB layout and wiring will also help to better reduce EMI interference to the system. In addition to tps61161, TPS61160 white LED drivers and tps61165 high brightness LED drivers of Texas Instruments all adopt secondary switching technology. For details, please refer to the product catalogue of Texas Instruments. (end)

Copyright © 2011 JIN SHI