Ultra High Density Offline Power Solution Reduces Losses

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The totem pole PFC controller provides high performance by cutting down the bridge losses at a cost effective price point

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. PFC stages are typically 97% efficient and the LLC circuit achieves similar performance.

However, the new NCP1680 critical conduction mode (CrM) totem pole PFC controller solution designed for ultra-high density offline power supplies, can replace the lossy diodes with switches in a ‘totem pole’ configuration and pulling in the boost PFC function for cutting down the bridge losses, significantly improving overall efficiency. Furthermore, 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 new NCP1680 CrM totem pole PFC controller employs novel current limit architecture and line phase detection while incorporating proven control algorithms that deliver a cost-effective Totem Pole PFC solution without compromising on performance. At the heart of this IC is an internally compensated digital loop control. The innovative device 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 synchronised turn-on during frequency foldback 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 350 W. With 230 Vac mains input, PFC circuits based upon the NCP1680 can achieve close to 99% efficiency at 300 W. Further by reducing component count, the cycle-by-cycle current limit is realised without the need for a Hall Effect sensor.

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

Housed in a tiny SOIC-16 package, the NCP1680 is available from ON Semiconductor. It 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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