DEGAUSSING DEVICE HAVING SERIES CONNECTED PTC AND NTC RESISTORS

• US 3,619,703 A
• Filed: 06/09/1969
• Issued: 11/09/1971
• Est. Priority Date: 06/17/1968
• Status: Expired due to Term

• Current Assignee: Hiroshi Yamashita, Kazuo Ishikawa, Masanori Fujimura
• Original Assignee: Hiroshi Yamashita, Kazuo Ishikawa, Masanori Fujimura
• Inventors: Yamashita, Hiroshi, Ishikawa, Kazuo, Fujimura, Masanori
• Primary Examiner(s): Segal, Robert
• Application Number:
  US04/831,451
• Time in Patent Office: 883 Days
• Field of Search: 315/8
• US Class Current: 315/8
• CPC Class Codes: H04N 9/29 using demagnetisation or compensation of external magnetic fields

Abstract

A degaussing device for the picture tube of a color television receiver magnetized by terrestrial magnetism causing colorcontamination is described. The device comprises a resistor having a positive temperature coefficient of resistance (PTC resistor), a resistor having a negative temperature coefficient of resistance (NTC resistor), and a coil wound on the picture tube for degaussing, the PTC resistor being connected in series to a parallel circuit of the NTC resistor and the degaussing coil, wherein the PTC resistor and the NTC resistor are in good thermal contact. A sufficiently large current for degaussing first flows through the coil and then the PTC resistor, the resistance of which is thereby raised, reduces the current. The NTC resistor heated by the PTC resistor therefore shows a lower resistance than that of the coil. Consequently, a further reduced current flows through the coil which gives little interference with the working of the picture tube.

Claims

1. A degaussing device for use with a picture tube of the type employed in color television receivers comprising a. a degaussing coil, b. a resistor having a negative coefficient of resistance (NTC) connected in parallel with said coil, and c. a resistor having a positive coefficient of resistance (PTC) connected in series with said parallel connected degaussing coil and NTC resistor, said NTC and PTC resistors being in thermal contact, the resistance of said NTC resistor decreasing rapidly and the resistance of said PTC resistor increasing rapidly with increasing temperature, the ratio at room temperature of the impedance of said coil to the impedance of said PTC resistor varying from 100:

1 to 1;

1 and to the impedance of said NTC resistor from 1;

100 to 1;

1; and

the ratio at elevated temperatures, after the rapid increase in resistance of said PTC resistor and the rapid decrease in resistance of said NTC resistor, of the impedance of said coil to the impedance of said PTC resistor varying from 1;

1000 to 1;

10 and to the impedance of said NTC resistor from 10;

1 to 1000;

1.

2. A degaussing device as claimed in claim 1, wherein said PTC resistor comprises a semiconductive barium titanate ceramic.

3. A degaussing device as claimed in claim 1, wherein said NTC resistor comprises a semiconductive ceramic based on manganese, cobalt chromium, titanium, nickel and copper oxides.