PFC (Power Factor Correction)

PFC circuits typically employ three modes of operation: Continuous Conduction Mode (CCM), Discontinuous Conduction Mode (DCM), and Critical Conduction Mode (CRM). These circuits place stringent demands on the MOS devices used to ensure system efficiency and thermal performance while maximizing system stability. The control loop response of a PFC circuit is relatively slow. To effectively suppress the 100-120Hz ripple generated by rectifying the 50-60Hz AC power supply, the response time of the PFC circuit usually needs to be on the order of tens of milliseconds. Without special optimization of control circuits and chips, PFC circuits are prone to generate violent inrush currents during startup, with peaks that may reach 5-10 times the steady-state operating current.When selecting a MOS for a PFC circuit, consider the following aspects:

---Switched characteristics, especially Ciss (Input Capacitance)

---EAS capability (Energy Absorption during avalanche breakdown)

---Surge current withstand capability

---ESD protection performance

LLC (Inductor-Inductor-Capacitor)

LLC resonant and Phase-Shifted Full-Bridge (PSFB) topologies are widely used in high-power resonant converters. These topologies greatly enhance the energy conversion efficiency of the converter by employing Zero Voltage Switching (ZVS) technology on the primary side and Zero Current Switching (ZCS) technology on the secondary side. This design not only significantly reduces switching losses but also achieves higher power density, making it ideal for high-performance applications such as server power supplies and electric vehicle charging stations.

To meet the specific needs of this type of topology, the T-Series VAST MOS power devices have been created. This innovative MOSFET is designed to be different from conventional Super Junction (SJ) MOSFETs, with its most notable feature being an extremely low Qg (Gate Charge). This feature not only optimizes high-frequency performance but also effectively suppresses the phenomenon of through-current under hard-switching conditions through faster reverse recovery, thus improving overall system reliability and efficiency.

Flyback

Common modes of operation for flyback switching power supplies include CCM and DCM. This type of topology is mainly suitable for small to medium power applications such as LED lighting and battery chargers. In these applications, MOSFET selection is often significantly influenced by the designer's preference and transformer parameters.

Our V/A Series VAST MOS product line covers the full voltage range of 500V to 1200V, providing a choice of MOSFETs for flyback topologies in all voltage classes within 600V-900V. For flyback auxiliary power supplies for 800V-1000V high voltage applications, the A-Series can also provide devices with higher breakdown voltage (BV).

Forward

Forward switching power supplies are mainly categorized into single-tube forward and dual-tube forward types for hard-switching applications. For single-tube forward topologies, the main switching MOSFET is stressed by up to twice the input voltage at turn-off due to the additional magnetic reset winding required for the transformer. Therefore, we recommend using MOSFETs with BV of 900V and higher in the V series VAST MOS to effectively cope with shocks caused by voltage changes.

The two-tube forward is a very stable topology that does not operate at a high frequency or have excessive inrush currents. The topology of the MOSFET is relatively loose, usually used with PFC in 200W~800W adapters, industrial power supplies, computer power supplies, or in environments with high stability requirements. We recommend the A series VAST MOSFET as the first choice.