Editing Analog television (section)

===CRT flyback power supply===
Most of the receiver's circuitry (at least in [[transistor]]- or [[integrated circuit|IC]]-based designs) operates from a comparatively low-voltage DC [[power supply]].  However, the [[anode]] connection for a [[cathode-ray tube]] requires a very [[high voltage]] (typically 10–30&nbsp;kV) for correct operation.

This voltage is not directly produced by the main power supply circuitry; instead, the receiver makes use of the circuitry used for horizontal scanning. [[Direct current]] (DC), is switched through the line output transformer, and [[alternating current]] (AC) is induced into the scan coils. At the end of each horizontal 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. This stored collapsing magnetic field energy can be captured. The reverse flow, short duration, (about 10% of the 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 transformer]] by the use of a rectifier which blocks this [[counter-electromotive force]]. A small value [[capacitor]] is connected across the scan-switching device. This tunes the circuit [[inductance]]s to [[Electrical resonance|resonate]] at a much higher frequency. This lengthens the flyback time from the extremely rapid decay rate that would result if they were electrically isolated during this short period. One of the secondary windings on the flyback transformer then feeds this brief high-voltage pulse to a [[Cockcroft–Walton generator]] design [[voltage multiplier]]. This produces the required high-voltage supply. A [[flyback converter]] is a power supply circuit operating on similar principles.

A typical modern design incorporates the flyback transformer and rectifier circuitry into a single unit with a captive output lead, known as a diode split line output transformer or an Integrated High Voltage Transformer (IHVT),<ref>{{cite web|url=http://www.miniwatt.info/mullard_tn77.pdf|title=Technical note 77&nbsp;– Diode Split for E.H.T. generation|work=Publication date&nbsp;– 1976|publisher=Mullard|access-date=24 November 2010|url-status=dead|archive-url=https://web.archive.org/web/20110721224854/http://www.miniwatt.info/mullard_tn77.pdf|archive-date=21 July 2011}}</ref> so that all high-voltage parts are enclosed. Earlier designs used a separate line output transformer and a well-insulated high-voltage multiplier unit. The high frequency (15&nbsp;kHz or so) of the horizontal scanning allows reasonably small components to be used.