Design Guideline on 150W Power Supply for LED

This application note describes a 150W rating design guideline for LED street lighting. The application design consists of CRM PFC and LLC SRC with high power factor and high power conversion efficiency using FL7930B and FAN7621S. To verify the validity of the application board and scheme, a demonstration board 150W (103V/1.46A) AC-DC converter was implemented and its results are presented in this application note. In CRM active PFC, the most popular topology is a boost converter. This is because boost converters can have continuous input current that can be manipulated with peak current mode control techniques to force peak current to track changes in line voltage. The FAN7930B is an active Power Factor Correction (PFC) controller for boost PFC applications that operate in critical conduction mode (CRM). Since it was first introduced in early 1990s, LLC-SRC (series resonant converter) has became a most popular topology because of its outstanding performance in areas such as the output regulation of switching frequency, ZVS capability for entire load range, low turn-off current, small resonant components using the integrated transformer, zero current switching (ZCS), and no reverse recovery loss on secondary rectifier. Figure 1 shows the typical application circuit, with the CRM PFC converter in the front end and the LLC SRC DC-DC converter in the back end. FL7930B and FAN7621S achieve high efficiency with medium power for 150W rating applications where CRM and LLC SRC operation with a two-stage shows best performance. CRM boost PFC converters can achieve better efficiency with light and medium power rating than Continuous Conduction Mode (CCM) boost PFC converters. These benefits result from the elimination of the reverse-recovery losses of the boost diode and Zero-Current Switching (ZCS). The LLC SRC DC-DC converter achieves higher efficiency than the conventional hard switching converter. The FL7930B provides a controlled on-time to regulate the output DC voltage and achieves natural power factor correction. The FAN7621S includes a high-side gate driver circuit, accurate current-controlled oscillator, frequency -limit circuit, soft-start, and built-in protections. The high-side gate drive circuit has a common-mode noise cancellation capability, which guarantees stable operation with excellent noise immunity. Using Zero Voltage Switching (ZVS) dramatically reduces switching losses and significantly improves efficiency. ZVS also reduces switching noise noticeably, which allows a small-sized Electromagnetic Interference (EMI) filter.