Out in Front: March 28, 1996

Secondary-side, or auxiliary, controllers usually use magnetic amplifiers, because they are more efficient than switching or linear regulators. Despite their advantages, however, magnetic amplifiers require expensive magnetic cores, design expertise, and extra component-sizing design margins to withstand maximum input voltage during short-circuit and other conditions. To avoid these drawbacks, the Linfinity Microelectronics LX1570 and LX1571 controllers’ architecture replaces the magnetic-amplifier core with a MOSFET.

The devices work in such applications as desktop computers and telecommunications and provide isolated multiple outputs, typically at currents greater than 3A. These ICs reduce peak-current requirements on the primary switch and allow higher operating frequencies than do conventional magnetic amplifiers. The devices also transfer power more efficiently than conventional units, because switch turn-on occurs before the ac input. In contrast, the leading edges of ac waveforms trigger magnetic amps, so the amplifiers can transfer only part of the incoming energy.

Both the resistive-sensing LX1570 (for output currents less than 4A) and the transformer-sensing LX1571 (for output currents greater than 4A) are available in eight-pin DIP and SOIC packages and cost $1.95 (1000).
—by Bill Schweber

Linfinity Microelectronics Inc, Garden Grove, CA, (714) 898-8121.