n the PCB.
Most modern desktop and laptop computers already have a DC-DC converter on the motherboard, to step down the voltage from the PSU or the battery to the CPU core voltage -- as low as 0.8 V for a low voltage CPU to typically 1.2-1.5 V for a desktop CPU as of 2007. Most laptop computers also have a DC-AC inverter to step up the voltage from the battery to drive the backlight, typically around 1000 Vrms.
Certain applications, such as in automobile industry and in some industrial settings, DC supply is chosen to avoid hum and interference and ease the integration of capacitors and batteries used to buffer the voltage. Most small aircraft use 28 volt DC, but larger aircraft often use 120 V AC at 400 Hz, though they often have a DC bus as well. Some submarines like the Soviet Alfa class submarine utilised two synchronous generators providing a variable three-phase current, 2 x 1500 kW, 400 V, 400 Hz.
In the case of TV sets, for example, one can test the excellent regulation of the power supply by using a variac. For example, in some models made by Philips, the power supply starts when the voltage reaches around 90 volts. From there, one can change the voltage with the variac, and go as low as 40 volts and as high as 260 (known such case that voltage was 360), and the image will show absolutely no alterations.
Wipo Publishes Patent of Fujitsu Technology Solutions Intellectual Property, Peter Busch for "Switched-Mode Power Supply Unit, Method of Operation and Use of a Switched-Mode Power Supply Unit in a Computer" (German Inventor)
Dec 31, 2012; GENEVA, Dec. 31 -- Publication No. WO/2012/171788 was published on Dec. 20.Title of the invention: "SWITCHED-MODE POWER SUPPLY...