Cost-effective and Compact PFC Controller for Ultra-high Density Offline Power Supplies

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ByLakshita Khanna 0

NCP1680 CrM Totem Pole PFC Controller

ON Semiconductor has added a critical conduction mode (CrM) totem pole PFC controller to their solution set for ultra-high density offline power supplies and power factor correction. The new NCP1680 CrM totem pole PFC controller employs novel current limit architecture and line phase detection while incorporating proven control algorithms to deliver a cost-effective solution without compromising on performance. It can accommodate any switch type, whether it is super junction silicon MOSFET or Wide Bandgap switches such as Silicon Carbide (SiC) or Gallium Nitride (GaN) devices. Moreover, only a few simple components are needed to create a fully functional, space and time-saving totem-pole PFC. The compactly designed controller enables high efficiency and allows communication with a downstream converter to optimize system performance.

In conventional PFC circuits, the rectifier bridge diodes account for around 4 W of losses in a 240 W power supply, representing around 20% of total losses. In contrast, PFC stages are typically 97% efficient and the LLC circuit achieves similar performance. Replacing the lossy diodes with switches in a ‘totem pole’ configuration and pulling in the boost PFC function can cut down the bridge losses and significantly improve overall efficiency. PFC circuits based upon the NCP1680 are capable of achieving close to 99% efficiency at 300 W.

An internally compensated digital loop control is the heart of this IC. This highly integrated device can enable power supply designs that operate with universal mains (90 – 265 Vac) at recommended power levels up to 350 W and employs a constant on-time CrM architecture with valley switching. Modern efficiency standards, including those that require high efficiency at light load, can also be met due to inbuilt discontinuous conduction mode (DCM) with valley synchronized turn-on during frequency foldback operation. The cycle-by-cycle current limit is achieved without the use of a Hall Effect sensor, thus reducing component count.

NCP1680 Controller Features

  • Totem Pole PFC Topology Eliminates Input Diode Bridge
  • Critical Conduction Mode (CRM) Operation
  • Discontinuous Conduction Mode (DCM) with Valley Turn On Under Light Load Condition
  • Frequency Foldback in DCM With 25 kHz Minimum Frequency
  • Skip Mode in Very Light Load Condition
  • Proprietary Current Sense Scheme
  • Digital Voltage Loop Compensation
  • AC Line Monitoring Circuit & AC Phase Detection
  • Near Unity Power Factor in All Operating Modes
  • PFC OK Indicator

The NCP1680 is housed in a tiny SOIC-16 package and is also available as part of an evaluation platform that allows rapid development and debugging of advanced totem pole PFC designs. 

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