Television and Monitor Power Circuits

A television or computer monitor needs several different supply voltages to operate, and the power circuits that provide them are a substantial part of the design. The set must convert the incoming mains supply into the low voltages required by signal-processing and control circuits, as well as the higher voltages needed by display components. Generating these efficiently, while keeping the equipment cool and compact, is the role of the power supply section.

Most modern televisions and monitors use a switched-mode power supply (SMPS). Instead of a heavy mains-frequency transformer, an SMPS rectifies the incoming mains, switches it on and off rapidly through a transistor and a small high-frequency transformer, and then rectifies and smooths the output. Because the transformer operates at a high frequency, it can be much smaller and lighter, and switching regulation makes the supply efficient and able to hold its outputs steady despite changes in load or mains voltage. Multiple secondary windings provide the different voltages the set requires.

Display technologies impose specific power demands. A cathode-ray tube requires a very high accelerating voltage, often produced by a voltage multiplier or by a flyback arrangement linked to the horizontal-deflection circuit, where the energy from each scan line is used to generate the high tension. In CRT sets, geometry corrections such as S-correction shape the deflection waveform so the image is not stretched at the edges of the curved screen. These high voltages make television power circuits hazardous to service, since dangerous charge can persist after the set is switched off.

Frequently asked questions

Why do televisions use switched-mode power supplies?

An SMPS switches the mains at high frequency, allowing a small, light transformer and efficient, well-regulated outputs compared with a bulky mains-frequency design.

How is the high voltage for a CRT produced?

Typically by a voltage multiplier or a flyback arrangement tied to the horizontal-deflection circuit, which generates the very high accelerating voltage the tube needs.

What is S-correction?

It shapes the deflection waveform to compensate for the curvature of a CRT screen, preventing the image from being stretched at the edges.