With the record highs in the LED lighting industry, energy conservation and environmental issues have received increasing attention. Lighting equipment with high brightness, low energy consumption and long life has become the trend of the lighting market. Low-cost LED drive technology has also become a research hotspot. Today's LED drivers enable smaller sizes, lower cost and higher efficiency.
Figure 1 Traditional secondary side regulated offline LED driver
For traditional lighting incandescent lamps, driving is a breeze, just connect the bulb directly to the voltage source. Most energy sources are in the form of a constant voltage, which makes the driving cost of incandescent lamps quite low. However, LEDs have a light output intensity that is proportional to its current and forward voltage drop and varies with temperature. Therefore, the LED requires a constant current to drive and requires additional circuitry. Traditionally, off-line constant current drivers for LEDs are typically implemented using an isolated flyback converter with an output current regulation circuit (see Figure 1). The actual LED voltage is measured by a sense resistor and then compared to the reference voltage value to obtain the error voltage. The error voltage is transmitted to the primary side via an optocoupler for controlling the duty cycle of the primary side switching device. Although this solution enables excellent LED current regulation, the output regulation circuit requires an optocoupler, a reference voltage, and a sense resistor, which greatly increases system cost and reduces overall efficiency.
Primary side regulation (PSR) technology may be the best solution to minimize the cost of off-line LED drivers. This technology requires only the information on the primary side of the driver to accurately control the LED current at the secondary side, eliminating the output current sense loss and eliminating all secondary feedback circuitry, thereby improving the offline LED driver without incurring significant cost. The efficiency of the design. In addition, the technology can adjust the LED driver output voltage without the need for a secondary-side feedback circuit, which is equivalent to providing an over-voltage over-voltage protection function to further ensure the reliability of the driver. This article will discuss the basic working principle of the primary-side regulation technique and introduce a highly integrated primary-side regulation PWM controller. This controller has several significant advantages over traditional secondary end regulation methods.
Figure 2 Primary-side regulated offline LED driver and its typical waveform
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