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At APEC this week, Fairchild announced the FAN9612 PFC (Power Factor Correction) controller IC that can deliver grater than 96% efficiency in AC-DC power supplies. The IC derives an efficiency advantage via the use of variable-frequency BCM (boundary conduction mode) operation that has typically been limited to relatively low-power supplies at 300W ratings or lower. The FAN9612 supports designs ranging from 100W to 1000W -- a range more akin to less-efficient fixed-frequency CCM (continuous conduction mode) operation.
Fairchild combined a boot-topology converter, the BCM operation, and a two-phase interleaved architecture to realize the efficiecny 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 degree phase shift. The summed signals is 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 over-voltage 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 designer 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. The IC sells for $1.30 (1000).
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