DEGAUSSING CIRCUIT FOR PORTABLE TELEVISION COLOR PICTURE TUBE

• US 3,784,868 A
• Filed: 10/20/1972
• Issued: 01/08/1974
• Est. Priority Date: 10/28/1971
• Status: Expired due to Term

• Current Assignee: Kinya Shinkai, Masato Izumisawa, Yoshitaka Abe
• Original Assignee: Kinya Shinkai, Masato Izumisawa, Yoshitaka Abe
• Inventors: Shinkai, Kinya, Abe, Yoshitaka, Izumisawa, Masato
• Primary Examiner(s): Gensler, Paul L.
• Application Number:
  US05/299,435
• Time in Patent Office: 445 Days
• Field of Search: 317/157.5 315/8
• US Class Current: 315/8
• CPC Class Codes: H04N 9/29 using demagnetisation or compensation of external magnetic fields

Abstract

A degaussing circuit for demagnetizing a color video tube in a portable television receiver in which the degaussing coil current is supplied through a thermistor from the horizontal output circuit of the portable television receiver.

Claims

1. An improved degaussing system for use with a color television of the type having one or more degaussing coils to demagnetize the color video picture tube, wherein the improvement comprises a source of direct current, a current switch, and an inductance, the inductance, the direct current source and the current switch being connected together to form a closed series circuit, and a degaussing circuit connected in parallel with the inductance, the degaussing circuit including at least one degaussing coil of the degaussing system, capacitance means connected in parallel with the one degaussing coil to form a circuit which is resonant at a predetermined frequency, and means for gradually decreasing the current in the degaussing coil during the warm up of the color video picture tube.

2. An improved degaussing system as recited in claim 1 wherein the predetermined frequency is substantially 15.75 KHz.

3. An improved degaussing system as recited in claim 1 wherein the degaussing circuit comprises at least a pair of degaussing coils connected in parallel with each other and the capacitor is connected in parallel with the degaussing coils.

4. An improved degaussing system as recited in claim 1 wherein the current switch comprises means for generating a saw-tooth shaped voltage waveform.

5. An improved degaussing system as recited in claim 1 wherein the means for gradually decreasing the current in the degaussing coil comprises a thermistor connected in series with the one degaussing coil.

6. An improved degaussing system for use with a color television having a horizontal output amplifier, a source of direct current, and a fly-back transformer having a primary winding connected in series with the source of direct current between the output terminals of the horizontal output amplifier, the degaussing system being of the type having one or more degaussing coils to demagnetize the color video picture tube, wherein the improvement comprises a capacitor connected in parallel with at least one of the degaussing coils to form a circuit which is resonant at an integral multiple of the frequency of the output signal from the horizontal amplifier, means for Connecting the degaussing coil between the leads of the fly-back transformer primary winding and means for gradually decreasing the current flow in the degaussing coil over a predetermined period of time beginning with the start of current flow in the degaussing coil.