Flyback transformer

The flyback transformer circuit was invented as a means of controlling the horizontal movement of the electron beam in a cathode-ray tube (CRT).

[citation needed] The primary winding of the flyback transformer is driven by a switch from a DC supply (usually a transistor).

If the secondary current is allowed to drop completely to zero (no energy stored in the core), then it is said that the transformer works in discontinuous mode.

The transformer can be equipped with extra windings whose sole purpose is to induce a relatively large voltage pulse when the magnetic field collapses as the input switch is turned off.

There is considerable energy stored in the magnetic field, and coupling it out via extra windings helps it to collapse quickly, and avoids the voltage flash over that might otherwise occur.

The pulse train coming from the flyback transformer windings is converted to direct current by a simple half-wave rectifier.

In modern displays, the LOPT, voltage multiplier, and rectifier are often integrated into a single package on the main circuit board.

There is usually a thickly insulated wire from the LOPT to the anode terminal (covered by a rubber cap) on the side of the picture tube.

Another advantage is that it provides a failsafe mechanism — should the horizontal deflection circuitry fail, the flyback transformer will cease operating and shut down the rest of the display, preventing the screen burn-in that would otherwise result from a stationary electron beam.

The flyback transformer operates CRT-display devices such as television sets and CRT computer monitors.