Browse Prior Art Database

VLMF Compensating Coil

IP.com Disclosure Number: IPCOM000034722D
Original Publication Date: 1989-Apr-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 2 page(s) / 45K

Publishing Venue

IBM

Related People

Anderson, CG: AUTHOR

Abstract

Very Low-Frequency Magnetic Field (VLMF) emissions from the scan circuits of cathode ray tube (CRT) display monitors must be restricted in order to satisfy national safety standards of several countries. The majority of emissions that originate from the scan coils on the CRT neck can be effectively suppressed by cancellation coils also fitted on the CRT yoke. Additional emissions from other components being driven at line scan rate must also be suppressed, but using scan cancellation coils for this purpose can mean interference with convergence of the CRT beam asymmetrically across the screen. This disclosure describes a method of cancelling out the majority of emissions from driver circuitry concentrated in one location, such as an analog driver card, without interfering with the convergence of the CRT beam.

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VLMF Compensating Coil

Very Low-Frequency Magnetic Field (VLMF) emissions from the scan circuits of cathode ray tube (CRT) display monitors must be restricted in order to satisfy national safety standards of several countries. The majority of emissions that originate from the scan coils on the CRT neck can be effectively suppressed by cancellation coils also fitted on the CRT yoke. Additional emissions from other components being driven at line scan rate must also be suppressed, but using scan cancellation coils for this purpose can mean interference with convergence of the CRT beam asymmetrically across the screen. This disclosure describes a method of cancelling out the majority of emissions from driver circuitry concentrated in one location, such as an analog driver card, without interfering with the convergence of the CRT beam. In order to compensate for the fields produced from the analogue card components, such as SMPS transformers and width and linearity coils, an extra field at line frequency and in anti-phase to the resultant of existing fields is introduced. Fig. 1 shows a CRT neck 1 with scanning coils Ys and compensating coils Yc wound on the same yoke (not shown). Coils Yc have an antiphase coil 2 connected in series with them via a polarized plug 3 and flexible cable 4. Coil 2 is mounted close to the line output transformer 5 on the analogue card 6. Fig. 2 shows the mechanical construction of the coil and mounting bracket. The coil used in this part...