LEDs are widely used in indicator lights, large billboards, scanners, fax machines, mobile phones, automotive lights, traffic lights, etc. due to their long life and low power consumption. However, in terms of illumination sources, current LEDs do not have the conditions to replace other light sources due to brightness and price. However, as the brightness continues to increase, LEDs will replace incandescent and fluorescent lamps in the near future, and prices will decline due to advances in mass production technology, and application demand will increase substantially.
1 XLT604 chip structure and function
The XLT604 is a PWM high efficiency LED driver control chip designed in BICMOS technology. It effectively drives high-brightness LEDs from an input voltage range of 8V (DC) to 450V (DC). The chip can drive external MOS-FETs at a fixed frequency of up to 300 kHz. And its frequency can be determined by external resistor programming. The externally highlighted LED string can be controlled in a constant current mode to maintain constant brightness and enhance the reliability of the LED. The constant current value can be determined by the external sampling resistor value, which varies from a few milliamps to 1 amp.
The LEDs driven by the XLT604 can be linearly adjusted by an external control voltage, or the brightness of the LED string can be adjusted by an external low-frequency PWM.
The functional block diagram of the XLT604 is shown in Figure 1.
Figure 1: Functional Block Diagram of the XLT604
The main functions of each pin are shown in Table 1.
Table 1: Main functions of each pin
2 XLT604 application circuit
The XLT604 is a control chip that can step down, boost, and buck-boost high-power LED strings. The chip is suitable for both AC input and DC input from 8 to 450 V. In the case of AC input, a passive power factor correction circuit can be added to the line to improve the power factor. The XLT604 can drive hundreds or thousands of LEDs in series or in series, and can adjust the constant current value to ensure LED brightness and extend life. The PWM_D terminal can adjust the brightness of the LED by the method of low-frequency pulse width modulation, and also serves as the enable end. When the terminal is suspended, the chip has no output control. In fact, the chip can also adjust the brightness of the LED through the linear voltage regulation of the LD terminal. Figure 2 shows a typical application circuit for the XLT604 in AC and DC inputs.
Figure 2: The buck drive circuit of the XLT604 in AC and DC input
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