Flyback Transformer

A flyback transformer (FBT), also called a line output transformer (LOPT), is a special type of electrical transformer. It was initially designed to generate high current sawtooth signals at a relatively high frequency. In modern applications it is used extensively in switched-mode power supplies for both low (3V) and high voltage (over 10 kV) supplies.

It was invented as a means of controlling the horizontal movement of the electron beam in a cathode ray tube (CRT). Unlike conventional transformers, a flyback transformer is not fed with a signal of the same waveshape as the intended output current. A convenient side effect of such a transformer is the considerable energy that is available in its magnetic circuit. This can be exploited using extra windings that can be used to provide power to operate other parts of the equipment. In particular, very high voltages are easily obtained using relatively few turns of winding which, once rectified, can provide the very high accelerating voltage for a CRT. Many more recent applications of such a transformer dispense with the need to produce high currents and just use the device as a relatively efficient means of producing a wide range of lower voltages using a transformer much smaller than a conventional mains transformer would be.

The flyback transformer is used in the operation of CRT-display devices such as television sets and CRT computer monitors. The voltage and frequency can each range over a wide scale depending on the device. For example, a large color TV CRT may require 20 to 50 kV with a horizontal scan rate of 15.734 kHz for NTSC devices. Unlike a power (or 'mains') transformer which uses an alternating current of 50 or 60 Hertz, a flyback transformer typically operates with switched currents at much higher frequencies in the range of 15 kHz to 50 kHz.

Read more about Flyback TransformerHow It Works, Practical Considerations, Construction, Failure

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Analogue Television Synchronization - Other Technical Information - CRT Flyback Power Supply Design and Operation Principles
... (DC), is switched though the line output transformer, and alternating current (AC) is induced into the scan coils ... scan line the magnetic field, which has built up in both transformer and scan coils by the current, is a source of latent electromagnetic energy ... line scan time) current from both the line output transformer and the horizontal scan coil is discharged again into the primary winding of the flyback ...
Flyback Transformer - Failure
... Flyback transformers are a frequent source of failure in CRT displays ... is blamed when the display has actually experienced a flyback transformer failure ... with the thin insulation required for the transformer to be of reasonable size, can result in leakage between the windings ...

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