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Switched Power Supply Synchronized to Display

IP.com Disclosure Number: IPCOM000039092D
Original Publication Date: 1987-Apr-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 60K

Publishing Venue

IBM

Related People

Hewett, SJ: AUTHOR

Abstract

A CRT display is supplied by a synchronized switched-mode power supply. In order to avoid interference on the display screen, the switched-mode power supply is run at half the horizontal scan rate such that both power supply switching edges occur within blanking time. The circuit disclosed uses a phase-locked loop to center the power supply ON time during alternate video times. With analog video on high performance monitors and user control over the level of background raster, it may be difficult to hide power supply switching edges on the display. This is particularly so when fast switching MOSFETs are used. The solution is to run the power supply at half the line frequency and to hide both power supply edges in the blanking time. To achieve the required range, the power supply ON time must be centered on the video time.

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Switched Power Supply Synchronized to Display

A CRT display is supplied by a synchronized switched-mode power supply. In order to avoid interference on the display screen, the switched-mode power supply is run at half the horizontal scan rate such that both power supply switching edges occur within blanking time. The circuit disclosed uses a phase- locked loop to center the power supply ON time during alternate video times. With analog video on high performance monitors and user control over the level of background raster, it may be difficult to hide power supply switching edges on the display. This is particularly so when fast switching MOSFETs are used. The solution is to run the power supply at half the line frequency and to hide both power supply edges in the blanking time. To achieve the required range, the power supply ON time must be centered on the video time. Typically, horizontal blanking time is approximately 18% of the line period and video display time is 82%. This allows a range of power supply duty cycle of 0.41 to 0.59 if the ON time is centered about every other video time. This is an adequate range for a continuous-mode flyback switched-mode power supply due to mains voltage variation.

(Image Omitted)

A Philips TDA 2582 power supply control module is used. This is a control module incorporating a phase-locked loop and all of the normal power supply housekeeping functions. Fig. 1 shows the circuit in block diagram form, and Fig. 2 shows typical w...