Nowadays there are cases of power failure. In such a situation, can save the emergency power supply. For example, from a car battery with a homemade voltage Converter 12/220 V. Saw: stock power is enough for several hours of modern television, the lighting of the lamp or other appliance with power up to 100 watts. The maximum current consumption from a battery does not exceed 11,5 A.
The electronic heart of the Converter is an oscillator assembled on the chip DD1. And frequency can, if necessary, to change the selection of the resistance R2.