Negative capacitance drives performance of active power factor controllers

Paul Boughton

Intersil has used the concept of negative capacitance to develop an active power factor controller that delivers minimal harmonic distortion (THD) and high power factor (PF) correction, reports NIck Flaherty.

Intersil has patented a new approach in negative capacitance technology which reduces EMI filter size, improves THD and PF and provides maximum efficiency over a wide input supply range and output power (input voltages from 85VAC to 270VAC and power range from 50W to 2kW).

This technology also minimizes zero crossing distortion, compensates for input filter capacitance PF displacement error and reduces the magnetic component size by up to 66 percent. For example, in an 85W power supply the EMI filter inductor can be reduced from 150uH to 56uH. The small external components result in a lower cost design with improved performance.

Negative capacitance is used to cancel positive parasitic capacitance, using mutual capacitance and inductors. It can also be generated using coupled inductor windings and a small capacitor. Depending on the coupling polarities and connected points of the capacitor, the generated negative capacitance can be on the input side, output side or top side of the network.

The power factor correction capability of the architecture is compatible with the requirements for a power factor higher than 0.9, as currently required by ENERGY STAR Programme Requirements for Computers Version 5.0. The ISL6730A also achieves light load efficiency using integrated skip-mode, and includes an internally clamped 12.5V gate driver delivering 1.5A peak current to the external power MOSFET.

The ISL6730A enables a reliable system that is fully protected with features such as cycle-by-cycle over-current, power limiter, over-temperature, input brownout, output over-voltage and under-voltage protection.

The ISL6730A is available now in compact 10-lead MSOP package, with prices starting at $0.95 each in 1,000-unit quantities.

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