Improved buck topology circuit structure LED driver boosts bulb power factor

The power factor requirements for LED bulbs are becoming more stringent, and the challenges of LED driver circuit design are increasing. Therefore, semiconductor manufacturers have developed a new generation of LED driver solutions that can meet the requirements of small size, high energy efficiency and high power factor by improving the buck topology. It helps developers design LED bulbs with a power factor of 0.9 or higher.

As incandescent bulbs are phased out, energy-efficient fluorescent lamps (CFLs) and light-emitting diodes (LEDs) will become the two lighting options that offer significant energy savings. Despite the maturity of CFL technology, white LEDs are developing rapidly, and the output lumens and efficacy of each LED component are getting higher and higher. The life of LED bulbs is more than twenty-five times that of standard incandescent bulbs, and the efficacy has exceeded the performance level of CFL bulbs.

The electronic ballast in most common CFL bulbs is capacitive and has a typical power factor (PF) of 0.5 to 0.6. This means that although the household pays only for the power indicated by the light bulb, the power company must actually produce a proportional Volt-amp charge, so a 13 watt CFL bulb with a power factor of 0.5 represents 26 volts - The load is only slightly less than 50% of the volt-ampere rating of an incandescent bulb of 60 watts.

Therefore, Energy Star requires a minimum power factor of 0.7 for LED bulbs with power greater than 5 watts, and commercial LED fixtures such as downlights and spotlights must have a minimum power factor of 0.9. Looking at the world, the power factor requirements for LED bulbs in the United States are not the most stringent; the most stringent is South Korea, which requires that all lamps with an input power exceeding 5 watts have a minimum power factor of 0.9, which will be designed for LED driver circuits. Designers are challenged to comprehensively evaluate energy efficiency, available space, and overall bill of materials (BOM) costs to provide optimized LED lighting solutions.

Import buck topology circuit LED bulb PF Great Leap Forward

Incandescent bulbs are designed for the voltage of a particular line; however, designers don't have to think about how to make a universally designed LED bulb popular around the world. In addition, the power supply within the LED bulb does not need to be electrically isolated from the load because it is integrated into a single housing; however, care must be taken in the design of the mechanism that must be physically compliant with safety requirements. With this in mind, designers no longer have to rely on isolated flyback topologies as the only power conversion architecture option.

Under certain boundary conditions, the buck topology can be optimized to provide good power factor. To provide a high power factor, the input current must be consistent with the line and grow proportionally as the voltage of the rectified line increases. The disadvantage of the buck topology is that the current flows when the input voltage Vin is greater than the output voltage Vout, so the LED string voltage must be lower than the line voltage. In most cases, this is not a problem because the number of series LEDs is relatively small compared to the line voltage, such as the total voltage of eight series LEDs is about 25 volts, less than 15% of the rectified 120 volt AC input peak voltage. .