US3495136A - Degaussing circuits - Google Patents

Degaussing circuits Download PDF

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Publication number
US3495136A
US3495136A US590624A US3495136DA US3495136A US 3495136 A US3495136 A US 3495136A US 590624 A US590624 A US 590624A US 3495136D A US3495136D A US 3495136DA US 3495136 A US3495136 A US 3495136A
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United States
Prior art keywords
resistor
coil
supply
circuit
degaussing
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Expired - Lifetime
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US590624A
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English (en)
Inventor
Jan Gerritsen
Adrianus Flubertus Kantelberg
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US Philips Corp
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US Philips Corp
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N9/00—Details of colour television systems
    • H04N9/12—Picture reproducers
    • H04N9/16—Picture reproducers using cathode ray tubes
    • H04N9/29—Picture reproducers using cathode ray tubes using demagnetisation or compensation of external magnetic fields

Definitions

  • Apparatus of this type generally comprise a degaussing circuit including a coil through which an alternating current flows which decreases in amplitude in the loaded condition.
  • the circuit also includes a supply resistor through which the coil is energized from an alternating voltage source, said supply resistor exhibiting an increasing resistance value in the loaded condition.
  • This disturbing remanence field occurs in particular in the demagnetization of the ferromagnetic parts magnetized by the terrestial magnetism, for example, the screening cap and the shadow mask of shadow mask colour television tubes.
  • the problem is solved by switching off the output current in the coil by an automatically operated switch when the amplitude of the output current in the coil is sufliciently small, since otherwise an undesired remanence is retained in the ferromagnetic parts to be degaussed.
  • the invention is based on the insight that, in particular in shadow mask colour television tubes, in the final condition of the demagnetisation the voltage across the degaussing coil must be made so small that a negligible magnetic remanence field is produced by the current in the coil. In this case we no longer require an expensive automatically operated switch.
  • the circuit arrangement according to the invention is characterized in that, in addition to the supply resistor, a second resistor is connected in series with the coil, the resistance value of which second resistor also increases in the loaded condition, and a third resistor is connected parallel to the series arrangement of the coil and the second resistor, the quotient of the resistance values of the third resistor and the supply resistor decreasing in the loaded condition.
  • FIGURE 1 shows an embodiment of the degaussing circuit in a colour television receiver
  • FIGURE 2 shows a second embodiment
  • FIGURE 3 shows a third embodiment.
  • the degaussing coil 1 is supplied by an alternating voltage source, for example, the supply lines 2, through a supply resistor 3.
  • the coil 1 may be divided into several fractional coils.
  • the supply resistor 3 is constructed from a seriesto-parallel circuit composed of the filaments 12 of the tubes in a colour television receiver.
  • the supply switch 4 of the colour television receiver When the supply switch 4 of the colour television receiver is actuated, the low resistance value of the filament circuit 3, associated with the cold condition, will rapidly increase to the higher resistance value which is associated with the higher temperature occurring in the operating condition of the colour television receiver.
  • an additional resistor having a positive temperature coefficient may be arranged in the receiver so that this resistor can take over the operation of the filament circuit 3 shown in FIGURE 1.
  • a resistor 5 having a positive temperature coefficient (PTC-resistor) is connected in series with the coil 1 and a resistor 6 having a negative temperature coefiicient (NTC-resistor) is connected parallel to the series arrangement of the coil 1 and the FTC-resistor 5.
  • the resistors 5 and 6, which are each included in a different branch of a parallel circuit, are thermally coupled by bringing them in intimate thermal contact with one another.
  • the NTC-resistor 6 Before actuating the supply switch 4, all the resistors are at ambient temperature and have such values that the NTC-resistor 6 is large relative to the small resistors 3 and 5.
  • the initial current occurring immediately after actuation of the switch 4 flows substantially through the series arrangement of the supply resistor 3, the coil 1, and the FTC-resistor 5.
  • the amplitude of this initial current is large as a result of the small initial values of the resistors 3 and 5.
  • This large initial current directly heats the supply resistor 3 and the PFC-resistor 5 so that the resistance of said resistors increases.
  • the NTC-resistor 6 is directly heated by the small current which initially flows through it and is indirectly heated by means of the thermal coupling with resistor 5, through which a large initial current is flowing.
  • the resistance value of the NTC-resistor 6 will rapidly decrease so that the current through said resistor can increase.
  • the resulting larger direct heating will produce a further decrease of its resistance value.
  • the resistance value of the NTC-resistor 6 will be small relative to that of the supply resistor 3 and the PTC-resistor 5.
  • the resistance value of the FTC-resistor 5 has increased so that only a negligible current will flow through the coil 1,
  • FIGURE 1 requires no extra components.
  • the FTC-resistor in series with the coil was directly connected to the supply lines through the power switch.
  • the filament circuit with a series connected NTC- reslstor as a current limiter constituted a separate circuit.
  • the colour television receiver comprises several filament circuits, at least one of these circuits may serve as a supply resistor 3.
  • a voltage-dependent resistor 7 (VDR) is connected in series with the coil 1.
  • the VDR is a device which has a small resistance when the voltage impressed across the resistor is high and a large resistance when the voltage across the resistor is low.
  • the resistor 8 is a normal resistor which maintains a substantially constant resistance value during operation. The resistors are proportioned so that when they are supplied from the supply lines, and with a cold filament circuit, the constant resistor 8 is large relative to the supply resistor 3 and the VDR. In the operating condition of the colour television receiver, the constant resistor 8 is small relative to the increased resistance of resistors 3 and 7.
  • the switching-on current pulse is determined by the series arrangement of the supply resistor 3, the coil 1, and the VDR 7. This current heats the filament circuit 3 so that the resistance value of the resistor 3 increases. Then a voltage division occurs of the supply voltage between the series arrangement of the resistors 3 and 8, in which the greater part of the supply voltage is across the resistor 3, so that as a result of the smaller voltage across the parallel circuit the resistance value of VDR 7 increases.
  • the supply current of the receiver will flow for the greater part through the resistor 8 across which a small voltage is set up, so that the resistance of VDR 7 becomes so large that the residual current flowing through the coil 1 produces a negligible magnetic field.
  • This circuit arrangement is very cheap since, besides the degaussing coil 1, only a normal resistor 8, which is suitable for the supply voltage, and the VDR 7 are required. This circuit is even cheaper than that shown in FIGURE 1, since, when the prices of the VDR 7 and the PTC-resistor 5 are the same, the more expensive NTC-resistor 6 is replaced by a cheaper ohmic resistor 8.
  • the filament circuit 3 of the receiver used in FIGURE 2 is replaced by two parallel-arranged FTC-resistors 9 and 10, one of which can be connected in the degaussing circuit by a separate two-way switch 11.
  • the switch 11 is of a very simple construction.
  • the PTC- resistor connected in the degaussing circuit for example, the resistor 9, operates the same way as the filament circuit 3 discussed with reference to FIGURE 2 and of degaussing occurs in the manner described with reference to FIGURE 2. If it is desirable to degauss once again during operation of the receiver, the switch 11 is switched to the cold FTC-resistor 10.
  • the PTC-resistor 9 After a short period of time the PTC-resistor 9 will cool down so that with this circuit arrangement it is possible to degauss repeatedly Without having to interrupt the voltage supply to the colour television receiver.
  • the PTC- resistors 9 and 10 no further temperature-dependent ele ments are included in the degaussing circuit.
  • degaussing circuits described are by no means to be used only for degaussing the ferromagnetic parts in a shadow mask colour television receiver.
  • a demagnetizing circuit as described with reference to FIGURE 3 can readily be used.
  • This circuit arrangement may also be used for the so-called fast erasing of magnetic tape in which a magnetized tape can be demagnetized in one pass.
  • a degaussing circuit for a body of magnetizable material comprising, a neutralizing coil adapted to be placed adjacent said magnetizable body, a source of alternating voltage, a supply resistor having a. positive temperature coefficient, a second resistor having a positive temperature coefiicient, means connecting said supply resistor, said coil, and said second resistor in series across said voltage source, a third resistor having a negative temperature coefiicient connected in parallel across the series combination of the coil and the second resistor, said supply resistor and said second resistor exhibiting an increase in resistance from the moment they are initially energized and for a given period of time thereafter so that the quotient of the resistance values of the third resistor and the supply resistor decreases during said time period, whereby the AC current flowing in said coil decreases in amplitude.
  • a circuit as claimed in claim 2 wherein the supply resistor comprises at least a portion of the filament circuit of an electric device.
  • a degaussing circuit for a body of magnetizable material comprising, a neutralizing coil adapted to be placed adjacent said magnetizable body, a source of alternating voltage, a supply resistor comprising at least one filament circuit of a television receiver, a second resistor, means connecting said supply resistor, said coil, and said second resistor in series across said voltage source, a third resistor connected in parallel across the series combination of the coil and the second resistor, said supply resistor and said second resistor exhibiting an increase in resistance from the moment they are initially energized and for a given period of time thereafter so that the quotient of the resistance values of the third resistor and the supply resistor decreases during said time period, whereby the AC current flowing in said coil decreases in amplitude.
  • a degaussing circuit for a body of magnetizable material comprising, a neutralizing coil adapted to be placed adjacent said magnetizable body, a source of alternatingvoltage, a supply resistor divided into at least two resistors each having a positive temperature coefficient, a second resistor, a switch having two positions, mean connecting said switch in circuit with said supply resistors, said coil, and said second resistors, so that in one position of the switch one supply resistor is connected in series with said coil and said second resistor across said voltage source and in the second switch position the other supply resistor is connected in series with said coil and said second resistor across said voltage source, and a third resistor connected in parallel across the series combination of the coil and the second resistor, said supply resistors and said second resistor exhibiting an increase in resistance from the moment they are initially energized and for a given period of time thereafter so that the quotient of the resistance values of the third resistor and the supply resistors decreases during said time period, whereby the AC current flowing in said coil decrease
  • a degaussing circuit for a body of magnetizable material comprising, a neutralizing coil adapted to be placed adjacent said magnetizable body, a source of alternating voltage, a supply resistor of the type having a positive temperature coeflicient, a second resistor of the type that is voltage-dependent, means connecting said supply resistor, said coil, and said second resistor in series across said voltage source, a third resistor that exhibits a substantially constant resistance over the operating range of the circuit and connected in parallel across the series combination of the coil and the second resistor, said supply resistor and said second resistor exhibiting an increase in resistance from the moment they are initially energized and for a given period of time thereafter so that the quotient of the resistance values of the third resistor and the supply resistor decreases during said time period, whereby the AC current flowing in said coil decreases in amplitude.
  • a degaussing circuit for a body of magnetizable material comprising, a neutralizing coil adapted to be placed adjacent said magnetizable body, a source of alternating voltage, a supply resistor comprising at least a portion of the filament circuit of a television receiver, a second resistor of the type that is voltage-dependent, means connecting said supply resistor, said coil, and said second resistor in series across said voltage source, a third resistor that exhibits a substantially constant resistance value during operation and connected in parallel across the series combination of the coil and the second resistor, said supply resistor and said second resistor exhibiting an increase in resistance from the moment they are initially energized and for a given period of time thereafter so that the quotient of the resistance values of the third resis tor and the supply resistor decreases during said time period, whereby the AC current flowing in said coil decreases in amplitude.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Video Image Reproduction Devices For Color Tv Systems (AREA)
  • Processing Of Solid Wastes (AREA)
US590624A 1965-11-03 1966-10-31 Degaussing circuits Expired - Lifetime US3495136A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
NL6514206A NL6514206A (enrdf_load_stackoverflow) 1965-11-03 1965-11-03

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US3495136A true US3495136A (en) 1970-02-10

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US590624A Expired - Lifetime US3495136A (en) 1965-11-03 1966-10-31 Degaussing circuits

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US (1) US3495136A (enrdf_load_stackoverflow)
ES (1) ES332940A1 (enrdf_load_stackoverflow)
FR (1) FR1502161A (enrdf_load_stackoverflow)
GB (1) GB1091659A (enrdf_load_stackoverflow)
NL (1) NL6514206A (enrdf_load_stackoverflow)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3619703A (en) * 1968-06-17 1971-11-09 Matsushita Electric Ind Co Ltd Degaussing device having series connected ptc and ntc resistors
US3886401A (en) * 1974-07-01 1975-05-27 Texas Instruments Inc Apparatus for accelerating cathode heating
US3944870A (en) * 1967-12-08 1976-03-16 Texas Instruments Incorporated Degaussing circuit for color television receivers
US4164775A (en) * 1976-07-14 1979-08-14 U.S. Philips Corporation Degaussing circuit in a color television receiver
DE3632598A1 (de) * 1986-09-25 1988-04-07 Siemens Ag Bauelement aus mindestens einem heissleiter und mindestens einem kaltleiter
US4760489A (en) * 1987-06-12 1988-07-26 Rca Licensing Corporation Video display degaussing apparatus
US5715130A (en) * 1996-02-19 1998-02-03 Murata Manufacturing Co., Ltd. Demagnetization circuit and components therefor
US5831508A (en) * 1996-12-09 1998-11-03 Murata Manufacturing Co., Ltd. Component for a demagnetization circuit

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3322998A (en) * 1964-08-31 1967-05-30 Rca Corp Color purity correcting apparatus for colored television picture tubes

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3322998A (en) * 1964-08-31 1967-05-30 Rca Corp Color purity correcting apparatus for colored television picture tubes

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3944870A (en) * 1967-12-08 1976-03-16 Texas Instruments Incorporated Degaussing circuit for color television receivers
US3619703A (en) * 1968-06-17 1971-11-09 Matsushita Electric Ind Co Ltd Degaussing device having series connected ptc and ntc resistors
US3886401A (en) * 1974-07-01 1975-05-27 Texas Instruments Inc Apparatus for accelerating cathode heating
US4164775A (en) * 1976-07-14 1979-08-14 U.S. Philips Corporation Degaussing circuit in a color television receiver
DE3632598A1 (de) * 1986-09-25 1988-04-07 Siemens Ag Bauelement aus mindestens einem heissleiter und mindestens einem kaltleiter
US4760489A (en) * 1987-06-12 1988-07-26 Rca Licensing Corporation Video display degaussing apparatus
US5715130A (en) * 1996-02-19 1998-02-03 Murata Manufacturing Co., Ltd. Demagnetization circuit and components therefor
US5831508A (en) * 1996-12-09 1998-11-03 Murata Manufacturing Co., Ltd. Component for a demagnetization circuit

Also Published As

Publication number Publication date
FR1502161A (fr) 1967-11-18
GB1091659A (en) 1967-11-22
ES332940A1 (es) 1967-12-01
NL6514206A (enrdf_load_stackoverflow) 1967-05-05

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