A flyback transformer is a type of transformer. It is used in the power supply that generates the high voltage needed for driving a cathode ray tube (CRT) or picture tube. It generates a voltage of a few kilovolts for a monochrome tube, or 10 to 30 kilovolts for a color tube. Unlike a mains (line) transformer, which works with sinusoidal alternating currents at 50 or 60 hertz, a flyback transformer operates with switched currents at much higher frequencies.