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Ultra high density offline power solutions

ON Semiconductor has released the industry’s first dedicated critical conduction mode (CrM) totem pole PFC controller for ultra-high density offline power supplies.

In conventional PFC circuits the rectifier bridge diodes account for around 4W of losses in a 240W power supply, which represents around 20% of total losses. In contrast, PFC stages are typically 97% efficient and the LLC circuit achieves similar performance.

However, replacing the lossy diodes with switches in a ‘totem pole’ configuration and pulling in the boost PFC function can further cut down the bridge losses and significantly improve overall efficiency. In addition, the NCP1680 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.

The 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 Totem Pole PFC solution. At the heart of this IC is an internally compensated digital loop control which 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 fold back operation.

This highly integrated device can enable power supply designs for telecom 5G, industrial and high performance computing, that operate with universal mains (90 – 265 Vac) at recommended power levels up to 350W. With 230 Vac mains input, PFC circuits based upon the NCP1680 are capable of achieving close to 99% efficiency at 300 W. Just a few simple components are required externally to realize a fully-featured totem pole PFC, thereby saving space and component cost. Further reducing component count, the cycle-by-cycle current limit is realised without the need for a Hall Effect sensor.

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

Depending on the switch technology selected for the fast leg of the totem pole, the NCP1680 can be used with either NCP51820 half bridge GaN HEMT gate driver or NCP51561 isolated SiC MOSFET gate driver. The NCP51561 is an isolated dual-channel gate driver with 4.5 A source and 9 A sink peak current capability.

The device is suitable for fast switching of silicon power MOSFETs and SiC-based MOSFET devices, offering short and matched propagation delays. Two independent and 5 kVRMS (UL1577 rated) galvanically isolated gate driver channels can be used as two low-side, two high-side switches or a half-bridge driver with programmable dead time. An enable pin will shut down both outputs simultaneously and the NCP51561 offers other important protection functions such as independent under-voltage lockout (UVLO) for both gate drivers and the enable function.

Author
Neil Tyler

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