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New Allegro SMPS regulators feature low EMI noise

Posted: 16 Aug 2006 ?? ?Print Version ?Bookmark and Share

Keywords:Allegro? STR-W67xx? primary regulator? XX? XX?

Allegro has announced a new line of low-power off-line SMPS primary regulators targeted at the consumer electronic, industrial appliance and home appliance markets. The STR-W67xx series includes quasi-resonant topology ICs designed for SMPS power supplies, showing lower EMI noise characteristics especially at more than 2MHz, Allegro said. They utilize a soft switching mechanism to turn on the internal MOSFET at a close point to ground level (VDS bottom point) through the resonant phenomenon of a primary inductor and resonant capacitor.

The bottom-skip function skips the first bottom of VDS and turns on the MOSFET at the second bottom point to minimize the increase of operational frequency at light output load, improving system-level efficiency over the entire load condition, said the company. Two standby functions reduce the input power at very light output load conditions: an auto-burst mode operation internally triggered by sensing on-time; and a manual standby mode that is executed by clamping the secondary output.

In general applications, the manual standby mode reduces the input power most as compared to the auto-burst mode. The soft-start function minimizes surge voltage and reduces power stress to secondary rectifying diodes during startup sequence. Allegro said various protections, such as overvoltage, overload, overcurrent, maximum ontime protection and avalanche-guaranteed MOSFET, secure good system-level reliability.

The package is a fully molded TO-220, which contains the controller chip and MOSFET and enables output powers up to 160W at 120Vac input, or 240W at 230Vac input.

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