US3754200A - Metal oxide varistor with selectively positionable intermediate electrode - Google Patents

Metal oxide varistor with selectively positionable intermediate electrode Download PDF

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Publication number
US3754200A
US3754200A US00188984A US3754200DA US3754200A US 3754200 A US3754200 A US 3754200A US 00188984 A US00188984 A US 00188984A US 3754200D A US3754200D A US 3754200DA US 3754200 A US3754200 A US 3754200A
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Prior art keywords
electrode
metal oxide
varistor
electrodes
oxide varistor
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US00188984A
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J Harnden
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General Electric Co
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General Electric Co
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
    • H01C7/10—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material voltage responsive, i.e. varistors
    • H01C7/102—Varistor boundary, e.g. surface layers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C10/00—Adjustable resistors
    • H01C10/46—Arrangements of fixed resistors with intervening connectors, e.g. taps

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  • oxIDE VARISTOR wITII SELECTIVELY POSITIONABLE INTERMEDIATE ELECTRODE My invention is directed to a metal oxide varistor having at least three electrodes with the third electrode being located to allow selection of a desired potential as compared to the first electrode.
  • V/C)alphu V/C)alphu
  • varistors having alphas in excess of within the current density range of 10' to 10 amperes per square centimeter may be made from bodies comprised or metal oxides.
  • the metal oxide body may be formed predominantly of zinc oxide with small quantities of one or more other metal oxides also being present.
  • Metal oxide varistors having alphas in excess of 10 are disclosed in Canadian Pat. No. 831,691, issued Jan. 6, 1970, for example. While the alphas of these metal oxide varistors is identified by the current density range of 10' to 10 amperes per square centimeter, which characteristically exhibits substantially constant alphas, it is appreciated that the alphas remain high also at higher and lower current densities, although some decline from maximum alpha values have been observed.
  • my invention is directed to the combination comprising a metal oxide varistor body means having an alpha in excess of 10 in the current density range of from 10* to 10 amperes per square centimeter.
  • a first electrode adapted to be biased to a first potential lies in ohmic contact withthe metal oxide varistor body means at a first location.
  • a second electrode adapted to bebiased to a second potential lies in ohmic contact with the metal oxide varistor body means at a second location spaced from the first location.
  • Third electrode means lies in ohmic contact with the metal oxide varistor body meansfor permitting selectable potentials intermediate the fii'st arid second potentials to be picked from the metal oxide varistor body means at any one of aplurality of selectable locations spaced from and mediate the first and second locations.
  • FIG. 1 is an elevation of one metal oxide varistor formed according to, my invention
  • FIG. 2 is a sectional view taken along section line 2-2 in FIG. 1;
  • FIG. 3 is a plan view of second embodiment of my invention.
  • FIG. 4 is a sectional view takenfalon g section line 4- 4 in FIG. 3; g
  • FIG. 5 is a schematic circuit diagram
  • FIG. 6 is a plan view of a third embodiment of my invention.
  • FIG. 7 is a plan view of a fourth embodiment of my invention.
  • a varistor is shown formed according to my invention including a metal oxide varistor body 102, which has an alpha as defined in equation (1 in excess of 10.
  • the metal oxide varistor body may be formed according to the teaching of the Canadian patent cited above or in any other known manner. As shown, the body is in the geometrical configuration of a cylindrical rod.
  • First and second electrodes 103 and 104 are located at opposite ends of the cylidrical rod. The electrodes may be ohmically conductively associated with the varistor body in any convenient conventional manner.
  • the third electrode Surrounding the rod is a third electrode 106.
  • the third electrode is in the form of a resilient band.
  • the opposite ends of the band are separated by a gap 108
  • the band is normally resiliently biased so that it compressively engages the surface of the rod.
  • the band is fixedly positioned between the electrodes 103 and 104 in predetermined spaced relation thereto.
  • the band In order to reposition the band it is merely necessary to apply a spreading force to the opposite ends thereof so as to enlarge the gap 108. This increases the diameter of the band and allows it to be slidably repositioned along the rod to any desired spacing with respect to the first and second electrodes.
  • FIGS. 3 and 4a varistor 200 is shown, which is an alternative embodiment of my invention.
  • a metal oxide varistor body 202 is supported on a dielectric substrate 204.
  • First and second electrodes 206 and 208 are ohmically conductively attached to the metal oxide varistor body at its opposite ends along a first major surface 210 thereof.
  • a third electrode means is formed by a plurality of discrete electrode elements 212a, 212b, 212e,
  • Each third electrode element is spaced both from the first and second electrodes and from each remaining element of the third electrode means.
  • the third electrode elements are positioned so that in order of progressive displacement from the first electrode every other (meaning every second or alternate) element is also laterally offset. In this way a larger number of elements may be located within a given lateral displacement along the major surface of the metal oxide varistor body than could be achieved if the elements were all aligned.
  • the edge of the element 212a most remote from the electrode 208 is aligned with the edge of the next successive element 212b, which (in terms of displacement distance from the electrode 208) is closest to the element 212a.
  • each of the successive elements is provided with an edge surface nearest the electrode 208 that is aligned with the edge surface most remote from the electrode 208 of the next nearest element to the electrode 208.
  • any lack of selectivity in spacing the elements with respect to the electrode 208 attributable to the requirement of laterally spacing the elements from each other is entirely avoided.
  • spacing of adjacent elements is achieved through the use of lateral offsets rather than by preventing elements from lying at certain distances from one of the first and second electrodes.
  • the metal oxide varistors 100 and 200 may be utilized in like or similar manner.
  • the first and second electrodes l03 and 104 may be electrically biased to lie at differing potentials, so that a potential difference is established between the electrodes.
  • the current flowing between the electrodes through the metal oxide varistor body 102 for a given potential difference between the electrodes will be a function of the conductivity of the metal oxide varistor body when subjected to that particular level of electrical stress.
  • the conductivity is a function both of A the composition of the metal oxide forming the body and of the distance between'the first and second electrodes.
  • the third electrode may readily be adjusted to a potential of 140 volts merely by locating the edge of the third electrode nearest the first electrode so that 40 percent of the length of the metal oxide varistor body lying between the first and second electrodes lies between the first and third electrodes.
  • the third electrode 106 of the varistor may be positioned at a selected potential intermediate the potentials of the electrodes 103 and 104 merely by expanding the band and sliding the electrode along the rod forming the metal oxide varistor body. When the expanding forces are removed from the band, its resilience will firmly locate the band in the desired position on the rod.
  • the third electrode means will assume a potential intermediate the applied potentials. While the third electrode means is comprised of elements 212a-212g each of which are fixedly positioned with respect to the first and second electrodes, it is apparent that by reason of their differing spacings with respect to the first and second electrodes each of the elements of the third electrode will lie at a different potential level. Accordingly, an intermediate potential may be selected merely by selecting one of the third electrode elements that lies at this potential. Whereas in the varistor 100 a continuous spectrum of intermediate potentials may be selected, in the varistor 200 the selectable intermediate potentials are in the form of a plurality of stepped increments.
  • the difference in value of the increments is noted to be a function merely of the width of the elements. If only one row of elements were employed, rather than two laterally offset rows as shown, the stepped increments of potential would be a function both of the width of the elements and of their spacing.
  • the varistors formed according to my invention are readily applicable to a variety of uses by reason of their capability for selective electrode spacings.
  • the first and third electrodes may be utilized.
  • the spacing between the first and third electrodes may be selectively chosen to give the desired current and voltage characteristics for the device, and the device may be substituted for any conventional two terminal varistor.
  • the first electrode may be biased to a potential differing from that of the second electrode, and an intermediate potential of a selectable value may be picked from the varistor body by the ohmic connection provided by the third electrode.
  • the third electrode may be biased to a potential either higher or lower than that of either the first and second electrodes.
  • an electrical circuit 300 is schematically shown comprised of input terminals 302 and 304 which may be attached to an alternating current or direct current potential source, not shown.
  • An electrical load 306 and a triac 308 are connected in series across the input terminals.
  • Connected to the gate lead of the triac is a diac 310.
  • a capacitor 312 is connected between the input terminal 304 and the diac.
  • the varistor is preferably connected across the input terminals by what correspond to the first and second electrodes in the varistors 100 and 200.
  • the varistor provides a selectably referenced third electrode which is connected to the diac and capacitor.
  • the third electrode When the input terminals 302 and 304 of the circuit are connected to an A-C or pulsating D-C potential source, proper spatial location of the third electrode with respect to the first and second electrodes can control the phase angle at which the triac is fired. As is well understood in the art, firing of the triac is achieved by firing the diac 310. The diac switches from an initially high impedance to a comparatively low impedance state when a predetermined potential difference thereacross is exceeded. The relationship of diac firing to application of a potential difference across the input terminals of the circuit is a function of the rate at which the capacitor 312 is charged. The potential difference between electrode of the varistor 314 connected to the input terminal 302 and the third electrode controls the rate at which the capacitor can be charged.
  • the varistor 314 is unique in that it performs a circuit function never before performable with a single electronic component.
  • a conventional resistive potentiometer for the varistor 314.
  • An increase in voltage applied across the terminals 302 and 304 would result in a proportionate acceleration of the rate at which the capacitor 312 is charged with a corresponding decrease in the phase angle of firing.
  • the third electrode is for all practical purposes clamped at a fixed maximum potential difference with respect to the input terminal 302, since the input terminals 302 and 304 are also effectively clamped at a fixed maximum potential difference thereacross.
  • the potential applied across the input terminals of the circuit may vary above a predetermined potential in an unpredicted manner without having any appreciable effect on the phase angle of firing.
  • the varistor 314 performs in a manner that could only be approximated with a resistive potentiometer which is connected across the input terminals of the circuit in parallel with a pair of backto-back Zener diodes. It is, of course, recognized that the relative invariancy with which the input potential can be clamped improves as the alpha of the varistor increases. Since the varistor 314 exhibits an alpha in excess of 10, it is capable of clamping the input potential to the circuit with a high degree of effectiveness.
  • a varistor 400 is formed according to my in- .vention comprised of a metal oxide varistor body 402.
  • the electrodes may be identical to electrodes 206 and 208.
  • the first electrode presents an edge surface 408 that is spaced from and parallel with an edge surface 410 of the second electrode.
  • a third electrode 412 is located in ohmic conductive relation with the exposed surface of the metal oxide varistor body between the first and second electrodes. The third electrode is located so that it presents an edge 414 that diverges across the width of varistor from the edge 410 of the second electrode.
  • the varistor 400 is formed so that the third electrode is a unitary element lying closer to the second electrode at its nearest approach than is deemed desirable in any contemplated application for the varistor. Also, the unitary third electrode at the greatest divergence of its edge 414 from the edge 410 of the second electrode lies at a greater distance than is deemed desirable for any contemplated application.
  • the varistor may then be precisely adjusted to yield a specific voltage and current relationship between the second and third electrodes merely by dividing the third electrode into two segments 416 and 418.
  • the nearest approach of the segment 418 to the edge 410 is precisely chosen to yield the desired voltage and current characteristics when a potential difference is established between the first and second electrodes and a lead attachment is made to the segment 418.
  • the third electrode may be conveniently segmented using techniques conventionally employed for trimming resistors in thick film integrated circuits.
  • FIG. 7 a varistor .500 is illustrated which may be identical to varistor 400, except that in place of the continuously diverging edge 414 associated with the third electrode a stepped edge 502 is provided. Each step along the edge is preferably substantially parallel to the edge of the adjacent electrode 504. The advantage of using a stepped edge is that a sharper currentvoltage knee or switching characteristic is obtained than is obtainable using a diverging edge.
  • the metal oxide varistor body in the form of a rod and in the form of a supported element.
  • the exact geometrical configuration of the metal oxide varistor body is not deemed critical to my invention.
  • the use of a slidable electrode is possible even with flat plate metal oxide varistor bodies.
  • flat plate metal oxide varistor bodies are preferred where the varistor is to be used with or form a part of an integrated circuit.
  • No particular means have been shown for attaching electrical connectors to the electrodes, since this is considered to be well within the ordinary skill of the art. It is noted that a number of mechanical arrangements are known to the art for slidably mounting electrodes that could be utilized in the prac-. tice of my invention without the exercise of invention.
  • the slidable third electrode make contact directly to the metal oxide varistor body directly it may make contact to metallized surface areas of the metal oxide varistor body.
  • the varistor 100 there may be provided a plurality of metal rings extending around the rod and spaced laterally along the rod between the first and second electrodes. The rings may be fixedly attached to the metal oxide varistor body in ohmic conductive relation therewith. The resilient band 106 would then slide over the rings and make electrical connection to whichever ring or rings it happened to overlie.
  • I claim: 1. The combination comprising metal oxide varistor body means having an alpha in excess of 10 in the current density range of from 10' to l0 amperes per square centimeter, afirst electrode adapted to be biased to a first potential lying in ohmic contact with said metal oxide varistor body means at a first location,
  • a second electrode adapted to be biased to a second potential lying in ohmic contact with said metal oxide varistor body means at a second location spaced from said first location
  • third electrode means lying in ohmic contact with said metal oxide varistor body means for permitting selectable potentials intermediate said first and second potentials to be picked from said metal oxide varistor body means, said third electrode means being formed of a resilient band, said band being resiliently biased to compressively engage said varistor body means.
  • said resilient band has first and second ends, said first and second ends being separated by a gap, said gap allowing said band to be disengaged from compressive engagement with said varistor body means by application of a spreading force to enlarge said gap so that said band is slidably repositionable along said varistor body means.

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  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Thermistors And Varistors (AREA)
US00188984A 1971-10-13 1971-10-13 Metal oxide varistor with selectively positionable intermediate electrode Expired - Lifetime US3754200A (en)

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US18898471A 1971-10-13 1971-10-13

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US (1) US3754200A (enExample)
JP (1) JPS4846858A (enExample)
DE (1) DE2250011A1 (enExample)
FR (1) FR2156322B1 (enExample)
GB (1) GB1365572A (enExample)
IT (1) IT968842B (enExample)
SE (1) SE383434B (enExample)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3959763A (en) * 1975-04-17 1976-05-25 General Signal Corporation Four terminal varistor
US4068281A (en) * 1976-09-15 1978-01-10 General Electric Company Thermally responsive metal oxide varistor transient suppression circuit
US4290041A (en) * 1978-02-10 1981-09-15 Nippon Electric Co., Ltd. Voltage dependent nonlinear resistor

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5066135U (enExample) * 1973-10-19 1975-06-14

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2935712A (en) * 1958-02-04 1960-05-03 Victory Engineering Corp Multi-terminal non-linear resistors
US3456228A (en) * 1964-07-01 1969-07-15 Charles S Wright Variable resistors
US3611073A (en) * 1968-12-02 1971-10-05 Matsushita Electric Industrial Co Ltd Diode comprising zinc oxide doped with gallium oxide used as a voltage variable resistor

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1501909A (fr) * 1966-09-28 1967-11-18 Lorraine Carbone Varistance variable avec la position des électrodes

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2935712A (en) * 1958-02-04 1960-05-03 Victory Engineering Corp Multi-terminal non-linear resistors
US3456228A (en) * 1964-07-01 1969-07-15 Charles S Wright Variable resistors
US3611073A (en) * 1968-12-02 1971-10-05 Matsushita Electric Industrial Co Ltd Diode comprising zinc oxide doped with gallium oxide used as a voltage variable resistor

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3959763A (en) * 1975-04-17 1976-05-25 General Signal Corporation Four terminal varistor
US4068281A (en) * 1976-09-15 1978-01-10 General Electric Company Thermally responsive metal oxide varistor transient suppression circuit
US4290041A (en) * 1978-02-10 1981-09-15 Nippon Electric Co., Ltd. Voltage dependent nonlinear resistor

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Publication number Publication date
IT968842B (it) 1974-03-20
FR2156322B1 (enExample) 1978-09-08
FR2156322A1 (enExample) 1973-05-25
SE383434B (sv) 1976-03-08
GB1365572A (en) 1974-09-04
DE2250011A1 (de) 1973-05-24
JPS4846858A (enExample) 1973-07-04

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