Vishay Siliconix (Malvern, PA) recently announced a new power MOSFET device that gives desktop computer manufacturers an affordable way to provide users with a quasi-instant power-up feature. Designed to facilitate the next generation of PCs implementing ACPI and OnNow, the new Vishay Siliconix Si4501DY switches the two voltage rails supplied by an ATX power supply. Allowing a part of the circuit to be isolated and powered from the standby supply, the main power supply and fan can be turned off while the computer is in the standby mode, thus giving the appearance of the computer being off.The complementary n- and p-channel MOSFETs are connected together internally and packaged in a LITTLEFOOT SO-8, functioning together as a single-pole double-throw switch with one control input. On-resistance at a 4.5V gate drive is 18 milliohms for the n-channel component and 42 milliohms for the p-channel – a record for a complementary device in the package type. The Si4501 is claimed to be particularly useful in designs where several loads may be grouped together, because of the low Rds(on) ratings that allow the Si4501DY to control currents up to 9A.The most efficient way to provide the apparent off-state and instant power-up is to allow a limited part of the computer's system to run from a standby power supply in isolation from the main power supply. By providing this function, the Si4501DY's n-channel component can function as the main power switch, while the p-channel component serves as the standby power switch. Vishay Siliconix is introducing a second device, the Si4500DY, for highly cost-sensitive designs. This device performs the same functions as the Si4501DY, but with higher maximum on-resistance ratings of 30 milliohms for the n-channel component and 65 milliohms for the p-channel component at a 4.5-V gate drive.Samples and production quantities of the Si4501DY and Si4500DY are available now. Pricing for U.S. delivery only in 100,000-piece quantities is $0.60 for the Si4501DY and $0.57 for the Si4500DY.