US3489947A - Ntc resistor in the high voltage supply - Google Patents

Ntc resistor in the high voltage supply Download PDF

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Publication number
US3489947A
US3489947A US715616A US3489947DA US3489947A US 3489947 A US3489947 A US 3489947A US 715616 A US715616 A US 715616A US 3489947D A US3489947D A US 3489947DA US 3489947 A US3489947 A US 3489947A
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United States
Prior art keywords
resistor
voltage
smoothing
circuit
high voltage
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Expired - Lifetime
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US715616A
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English (en)
Inventor
Anthonie Jannis Moggre
Ferdinand Geene
Jan Jacobus Rotte
Egbertus Johannes He Schaminee
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US Philips Corp
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US Philips Corp
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/14—Arrangements for reducing ripples from DC input or output
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N3/00—Scanning details of television systems; Combination thereof with generation of supply voltages
    • H04N3/10—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical
    • H04N3/16—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical by deflecting electron beam in cathode-ray tube, e.g. scanning corrections
    • H04N3/18—Generation of supply voltages, in combination with electron beam deflecting

Definitions

  • This invention relates to a device for continuously supplying a high DC voltage to an electrode of a cathode ray tube.
  • the device comprises a high-voltage generator having an output terminal at which a periodically occurring pulsatory high voltage is produced.
  • the output terminal is connected to the said electrode through a rectifying and a smoothing circuit.
  • cathode ray tubes such as, for example, in electron microscopy, radiology, radar and television.
  • the design of the cathode ray tubes and the value of the required high DC voltage vary greatly for different fields of application. A great variation also occurs in any one field, such as may be illustrated in television by monochrome, colour or projection television in which a high voltage of 15 kv., 25 kv., or 50 kv. to 80 kv. is required for the anode electrode of the diiferently constructed television display tubes.
  • the smoothing circuit is generally formed by a resistor connected between the rectifier circuit and the electrode of the cathode ray tube and by the capacitance relative to ground of the said electrode.
  • the pulsatory high voltage generated by the high-voltage generator and rectifed by the rectifying circuit should be supplied as a substantially constant high DC voltage to the anode of the colour television display tube through the said smoothing circuit. This may be achieved by means of a proper choice of the time constant of the smoothing circuit relative to the recurrence period of the pulsatory voltage. Since the smoothing capacitance is determined by the capacitance of the anode relative to ground, the smoothing resistor must be properly matched and must have a high value for satisfactory smoothing.
  • the burr possibly burns away and hence the cause of the flashover is eliminated, but on the other hand the rectified high voltage is set up across the series arrangement of the smoothing resistor and the arc resistor in the form of a step function.
  • a voltage division occurs, while proportionally therewith the power generated by the high-voltage generator is dissipated in the smoothing resistor and the arc resistor.
  • the smoothing resistor it is desirable for the smoothing resistor to have a small value relative to the arc resistor during fiashover.
  • the smoothing resistor would otherwise be destroyed due to the high instantaneous power dissipation and the large high voltage (for colour television the highvoltage generator supplies a nominal power of, for example, 30 w. at 25 kv.).
  • the smoothing resistor must have a high value on the one hand for satisfactory smoothing of the rectified high voltage, and on the other hand a low value in case the anode is short-circuited to ground. It is known that this can be realized by placing a spark gap in parallel with the smoothing resistor. Said solution is very unattractive and is inherently dangerous. The reproducibility of the flashover voltage of a spark gap is in fact very poor. Furthermore, the occurrence of a fiashover introduces oscillations into the entire device with all the adverse results attended therewith. It is also known to give the smoothing resistor a resistance value which lies between the said high and low values. It is evident that this compromise will result in both a poorly smoothed high voltage for the anode and in an unsafe device. Said solution is very expensive since the smoothing resistor must be considerably overrated.
  • An object of the device according to the invention is to obviate the above-mentioned drawbacks concerning smoothing and short circuit.
  • the invention is characterized in that in order to obtain a device supplying a substantially constant high DC voltage that is protected against short circuits, the filter circuit comprises a smoothing resistor having a negative temperature coefficient which connects the rectifying circuit to the said electrode.
  • the invention is based on the concept that the object aimed at can be reached with a smoothing resistor having a non-linear current-voltage characteristic and having a time delay in the resistance variation as a function of the impressed varying voltage.
  • VDR voltage-dependent resistor
  • the ripple on the rectified high voltage will in fact cause an immediately occurring variation of resistance with :a VDR so that a poor smoothing action is obtained.
  • a VDR across which part of the high voltage is set up during fiashover will experience changes in material so that its properties also change.
  • the sole figure shows a high-voltage generator 1 comprising a transformer 2, a DC voltage source 3 and a switching element 4.
  • the transformer 2 is constructed with a primary winding 5 to which a possibly parasitic capacitor 6 and a series arrangement of a voltage source 3 and switching element 4 are connected in parallel,
  • the switching element 4 is generally switched at the line deflection frequency.
  • the alternate closing and opening of switching element 4 excites the oscillatory circuit formed by the capacitor 6 and the primary 5.
  • the result is that a pulsatory high voltage is induced in the secondary winding 7 of the transformer 2. This voltage is shown near the output terminal 8 of the high-voltage generator 1.
  • the output terminal 8 is connected to a smoothing circuit through a rectifying circuit arrangement formed by a rectifier 9 and a capacitor 10, which is connected to ground at its other end.
  • said smoothing circuit comprises a resistor 11 having a negative temperature coefficient (NTC) as the smoothing resistor.
  • NTC negative temperature coefficient
  • the other end of the NTC resistor 11 is connected to an anode 12 of a colour television display tube 13.
  • the capacitance of the anode 12 relative to ground or the outer coating 14 of the tube 13 is indicated by a capacitor 12'.
  • Anode 12 is applied as an Aquadag layer on the inner wall of the cone of the display tube 13, shown as a shadow mask tube.
  • the shadow mask 15 is connected to the anode 12.
  • the shadow mask tube 13 is provided with means 16 for generating, accelerating and focusing three electron beams, not shown. Further components which are irrelevant for an understanding of the invention, but are required for a satisfactory operation of tube 13, are not shown in figure since they are well known in the art.
  • a maximum current of 1.2 ma may flow through the NTC-resistor 11 in the embodiment shown (30 w, at kv.).
  • This resistor is chosen in a manner such that the resistance value is, for example, 33 k at a current of 1 ma.
  • an anode-ground capacitance 12 of approximately 2200 pf.
  • a satisfactory smoothing by means of a smoothing resistor 11 having a high value is obtained in the manner described, while said resistor is not destroyed in case of a short circuit of the anode-ground capacitance 12.
  • NTC-resistor 11 was found not to be destroyed during the comparatively long short-circuit period, which is determined by a safety circuit (not shown) associated with the high-voltage generator 1.
  • a current-dependent short-circuit safety element is used in the device, e.g., a fuse, then it will be possible for said device to be switched off due to the larger short-circuit current that occurs as a result of the NTC-resistor having decreased in value. Without the decrease in resistance of resistor 11, the short circuit current might be too small to blow the fuse, so that the resistor would finally burn out.
  • High-voltage generator 1 may be constructed both as a pulse and a fly-back driven high-voltage generator.
  • the pulse type is. sometimes used when a large high-voltage power must be generated, to which end a special transformer 2 has been placed in, for example, a colour television receiver or projection television apparatus.
  • the flyback driven type simultaneously generates a saw-tooth deflecting current for the line deflection coils of a television display tube 13. This is shown in the figure by the series arrangement of a line deflection coil 17 and a capacitor 18 connected inparallel with primary winding 5 of transformer 2.
  • the flyback driven high-voltage generator may then be provided with a booster or a shunt efficiency diode.
  • Diode 9 may also be constructed as a semiconductor diode while capacitor 10 may be a coaxial cable.
  • the device according to the invention may be provided with a control circuit which, apart from the ripple, must receive a generated high voltage at a more or less constant value. Voltage multiplication arrangements may also be used.
  • Apparatus for continuously supplying a substantially constant high DC voltage to an electrode of a cathode ray tube comprising, a high voltage generator having an output terminal at which periodically occurring high voltage pulses are produced, rectifying means including a capacitor for developing said high DC voltage, means connecting said rectifying means to said output terminal, and a filter circuit coupled between said rectifying means and said tube electrode and including a resistor having a negative temperature coeflicient of resistance, said resistor having a given time delay in its resistance variation as a function of applied voltage such that the resistance remains substantially constant at the ripple frequency of said high voltage but rapidly decreases to a very low value in the event said electrode is short-circuited.
  • said rectifying means comprises a diode connected in series with said capacitor across said high voltage generator, and said negative temperature coeflicient resistor is connected in series with said diode between the output terminal and the tube electrode.
  • said high voltage generator comprises a transformer connected to said output terminal, and a DC voltage source and a switching element coupled to said transformer.
  • said high voltage generator comprises a flyback driven high voltage generator that simultaneously generates a deflection current for the line deflection coils of said cathode ray tube.
  • a display system including a cathode ray tube having a cathode and at least one electrode that requires a substantially constant high DC voltage relative to the cathode, the improvement comprising, a source of high voltage pulses, a rectifier circuit comprising a diode and a capacitor connected across said pulse voltage source, and a filter circuit connected between the output of said rectifier circuit and said tube electrode, said filter circuit including a series connected negative tempertaure coeflicient resistor that exhibits a predetermined time delay in its resistance variation as a function of applied voltage so that said resistor does not respond to the normally occurring frequency components of the voltage supplied by said pulse voltage source.
  • a display system as claimed in claim 6 wherein said pulse voltage source comprises the horizontal deflection transformer of a magnetic beam deflection system for said cathode ray tube.
  • a circuit for supplying a high DC voltage to an electrode of a cathode ray tube comprising, a source of high voltage, a rectifier circuit comprising a diode and a capacitor connected across said voltage source, and a filter circuit connected between the output of said rectifier circuit and said tube electrode, said filter circuit including a series connected negative temperatur coeflficient resistor having a negative resistance region in its V-I characteristic.
  • a circuit as claimed in claim 8 further comprising means directly connecting said negative temperature coeflicient resistor between the output electrode of said diode RODNEY D. BENNETT, IR. Primary Examiner and Sam tube electrode JOSEPH G. BAXTER, Assistant Examiner References Cited s Cl R UNITED STATES PATENTS 2,628,326 2/1953 Bridges 31S27

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Vessels, Lead-In Wires, Accessory Apparatuses For Cathode-Ray Tubes (AREA)
  • Details Of Television Scanning (AREA)
  • Thermistors And Varistors (AREA)
  • Dc-Dc Converters (AREA)
US715616A 1967-04-08 1968-03-25 Ntc resistor in the high voltage supply Expired - Lifetime US3489947A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
NL6705023A NL6705023A (en:Method) 1967-04-08 1967-04-08

Publications (1)

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US3489947A true US3489947A (en) 1970-01-13

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US715616A Expired - Lifetime US3489947A (en) 1967-04-08 1968-03-25 Ntc resistor in the high voltage supply

Country Status (10)

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US (1) US3489947A (en:Method)
JP (1) JPS4613776B1 (en:Method)
AT (1) AT275620B (en:Method)
BE (1) BE713404A (en:Method)
CH (1) CH474896A (en:Method)
DE (1) DE1616295A1 (en:Method)
ES (1) ES352485A1 (en:Method)
FR (1) FR1568376A (en:Method)
GB (1) GB1210019A (en:Method)
NL (1) NL6705023A (en:Method)

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2628326A (en) * 1951-03-10 1953-02-10 Zenith Radio Corp Television apparatus

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2628326A (en) * 1951-03-10 1953-02-10 Zenith Radio Corp Television apparatus

Also Published As

Publication number Publication date
CH474896A (de) 1969-06-30
GB1210019A (en) 1970-10-28
FR1568376A (en:Method) 1969-05-23
JPS4613776B1 (en:Method) 1971-04-13
NL6705023A (en:Method) 1968-10-09
AT275620B (de) 1969-10-27
BE713404A (en:Method) 1968-10-08
ES352485A1 (es) 1969-12-16
DE1616295A1 (de) 1971-03-25

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