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Avoiding CRT Display Distortion from Switching Power Supplies

IP.com Disclosure Number: IPCOM000050888D
Original Publication Date: 1982-Dec-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Homan, LC: AUTHOR [+2]

Abstract

A high-frequency switching-type power supply is frequency-synchronized to the horizontal flyback of a CRT display, to avoid raster distortion in the CRT due to stray electromagnetic fields in the nearby power supply.

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Avoiding CRT Display Distortion from Switching Power Supplies

A high-frequency switching-type power supply is frequency-synchronized to the horizontal flyback of a CRT display, to avoid raster distortion in the CRT due to stray electromagnetic fields in the nearby power supply.

CRT display 11 and power-supply oscillator 12 start independently when AC line voltage is first applied. The frequency of oscillator 12 is designed to be close to that of flyback transformer 13 in display 11. A loop of wire 14, preferably AC power wire, passes through the yoke of transformer 13 to pick up a small amount of energy at an isolated voltage level. This energy is coupled to oscillator 12 by circuit 15 through removable connectors 16. When V1 goes positive, Q1 turns off and Q2 conducts. When V1 goes negative, Q2 turns off and Q1 conducts because of the charge stored in C1. The collector of Q2 provides a conventional synchronizing signal 16 to oscillator 12, to force its frequency to lock in with the frequency of flyback transformer 13.

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