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Meaning for fly-back transformer

The flyback transformer may be defined as an integrated transformer which implies it has built in rectifiers and divider networks and several low voltage windings. It is the function of a flyback transformer in a monitor or television to generate high voltage about 24 kilovolts Direct current (DC) to picture tube or CRT.

The earlier version of flyback transformer had its high voltage diode outside and was called tripler. From the maintenance point of view, if any of the diodes became corrupt, you just had to replace the triple. But today, the flyback transformer is available as a single piece and all the high voltage diodes are molded inside the casing. The disadvantage is if one of the diodes shorted inside you have to replace the entire unit.

The external features of a flyback transformer is a voltage divider and inside the divider is a resistor networks control where the top control is for focus adjustment and the bottom one is for screen or G2. To facilitate functioning of a flyback transformer, a B+ supply voltage must enter the primary winding and at the same time a horizontal output transistor (HOT) must switch.

The HOT switching is done by horizontal driver circuit with the aid of a horizontal driver transformer. If one of the B+ voltage or signal to the HOT is missing, then the flyback transformer obviously will not work. Of course there are also other factors that cause malfunctioning of a flyback transformer.

A flyback transformer that is also called as a line output transformer (FBT or LOPT) is a kind of transformer used in the power supply of a cathode ray tube that generates the high voltage required ranging from a few kilovots for an oscilloscope tube to 20 to 30 KV needed for a color TV tube. A flyback transformer operates with switched currents at much higher frequencies, usually in the range of 17 kHz to 50 kHz. Unlike the mains transformers and audio transformers, a flyback transformer is meant not merely to transfer energy, but also to store it for a significant fraction of the switching period. The alternating current (AC) coming from the flyback transformer is converted to direct current (DC) by a high-voltage rectifier. If the output voltage of the flyback transformer is not high enough, then the rectifier is replaced by a voltage multiplier. Early color television s ets used a regulator to control the high voltage. The rectified voltage is then used to supply the anode of the cathode ray tube.

The principal difference between a flyback transformer and a regular transformer is that a flyback transformer is designed to store energy in its magnetic circuit whereas a regular transformer is designed to transfer energy from its primary to secondary and to minimize stored energy. Unlike mains transformers and audio transformers, a flyback transformer is designed not merely to transfer energy, but also to store it for a significant fraction of the switching period. This is achieved by winding the coils on a ferrite core with air gap. This air gap increases the relectance of the magnetic circuit and thus its capacity to store energy. A flyback transformer has current flowing either in its primary or in its secondary - but not to both at the same time. The reluctance of the magnetic circuit of a flyback transformer is usually much higher than that of a regular transformer. The voltages applied to a flyback transformer on the primary side are almost always rectangular whereas regul ar transformers usually have sinusoidal voltages applied to them.