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PFC controller IC is extremely efficient

Posted: 20 Feb 2009 ?? ?Print Version ?Bookmark and Share

Keywords:controller PFC? PFC IC? AC DC efficiency?

At this year's Applied Power Electronics Conference and Exposition (APEC), Fairchild Semiconductor Inc. announced the FAN9612 power-factor correction (PFC) controller IC that can deliver greater than 96 percent efficiency in AC/DC power supplies.

The IC derives an efficiency advantage via the use of variable-frequency boundary conduction mode (BCM) operation that has typically been limited to relatively low-power supplies at 300W ratings or lower. The FAN9612 supports designs ranging from 100W to 1,000Wa range more akin to less-efficient fixed-frequency continuous conduction mode operation.

Fairchild combined a boot-topology converter, the BCM operation and a two-phase interleaved architecture to realize the efficiency benefits of the new IC. The two-phase design delivers the advantages of higher switching frequencies such as smaller components without the downside of EMI filter problems. The two converters inherent in the design operate in parallel with a 180 phase shift. The summed signals are relatively free of ripple current that's cancelled via precise matching of the phase differential.

BCM, meanwhile, delivers higher efficiency by minimizing switching losses. In a single-phase design, BCM would prove impractical at the higher power levels because of ripple current. But the dual-phase architecture extends BCM to the kW range.

Other features include dual-output overvoltage protection including latching and non-latching options. The design implements over-current and power-limit protection for each channel. The IC integrates programmable closed-loop soft-start operation that minimizes overshoot at startup.

Finally, the FAN9612 implements automatic phase control that's increasingly popular in digital power controllers. Phase shedding provides a relatively flat efficiency curve across a broad load range. The converters are designed for maximum efficiency at relatively high load levels. When the load drops, the converter can shed or shut down one phase and keep the remaining phase operating in the sweet spot of the load efficiency curve.

- Maury Wright
Power Management DesignLine

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