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Topic: Varistor

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	Varistor - Wikipedia, the free encyclopedia
		A varistor is an electronic component with a significant non-ohmic current-voltage characteristic.
		Varistors are often used to protect circuits against excessive transient voltages.
		When varistors are used to protect communications lines (such as phone lines used for modems), their capacitance is also important because high capacitance would absorb high-frequency signals, thereby reducing the available bandwidth of the line being protected.
	en.wikipedia.org /wiki/Varistor (422 words)

	Varistor -- Facts, Info, and Encyclopedia article (Site not responding. Last check: 2007-09-17)
		A varistor is a type of (An electrical device that resists the flow of electrical current) resistor with a significantly non-ohmic (A steady flow (usually from natural causes)) current- (The rate at which energy is drawn from a source that produces a flow of electricity in a circuit; expressed in volts) voltage characteristic.
		The most common type of varistor is the (Any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc.) metal (Any compound of oxygen with another element or a radical) oxide varistor, or MOV.
		If the size of the transient pulse (often measured in (A unit of electrical energy equal to the work done when a current of one ampere passes through a resistance of one ohm for one second) joules) is too high, the device may melt, or otherwise be damaged.
	www.absoluteastronomy.com /encyclopedia/v/va/varistor.htm (542 words)

	Metal oxide varistor pressure sensor and method - Patent 4155262
		The leakage current in metal oxide varistor materials is found to vary as a function of pressure in the range from approximately 0.5 kbar to approximately 10 kbar.
		The varistor is also electrically connected to a leakage current tester 3 which functions to measure the current flow when the voltage applied to the varistor is equal to one-half of the voltage needed to produce a current of 1 ma through the varistor.
		Varistor pressure sensors and pressure memory devices of the present invention provide highly sensitive sensor in the pressure range of approximately 0.5 kbar to approximately 10 kbar.
	www.freepatentsonline.com /4155262.html (1803 words)

	Thick film varistor - Patent 4333861
		The electric characteristics of a varistor are expressed by the following equation: I=(V/C).sup.n, where V is the voltage across the varistor, I is the current flowing through the varistor, C is a constant equivalent to the electrical resistance at a given voltage and n is a numerical value greater than 1.
		This thick film varistor has a lower varistor voltage than that of a conventional thick film varistor having a similar n-value, and is more stable with respect to the varistor voltage to a load test than is the conventional thick film varistor.
		The varistor paste applied to the insulating base is dried, if necessary, to remove the liquid vehicle and then fired in an electrical furnace at a temperature at which the glass frit fuses so as to bond the tin oxide powder particles and to make the varistor film firmly adhere to the insulating base.
	www.freepatentsonline.com /4333861.html (2126 words)

	Varistor Technology Consulting
		A recognized authority on the manufacture, operation, and understanding of metal oxide varistors, Dr. Levinson is familiar with the field of arresters and transient protective devices in general and the utilization of metal oxide technology for this purpose.
		The varistors are produced by a ceramic sintering process that provides a structure largely comprised of conductive ZnO grains surrounded by thin electrically insulating barriers.
		Varistors are inherently multijunction grain-boundary devices and any transient surge energy to be absorbed when the device acts in a protective mode is distributed among the many ZnO grain junctions.
	home.nycap.rr.com /lionellevinson (916 words)

	Metal Oxide Varistor Degradation (Site not responding. Last check: 2007-09-17)
		Littelfuse publishes varistor pulse rating curves that are shown in figure 3.
		Varistors can dissipate a relative small amount of average power compared to surge power and are not suitable for repetitive applications that involve substantial amounts of power dissipation.
		The number of "varistor hours" on test at any time can be computed by adding the lives, in hours, of the varistors that have failed up to the moment of estimation, to the lives, in hours, of the varistors observed that have not failed.
	www.iaei.org /magazine/04_b/04_b_brown.htm (2725 words)

	Voltage nonlinear resistor, method for fabricating the same, and varistor - US Patent 6507077 (Site not responding. Last check: 2007-09-17)
		Therefore, in order to decrease the capacitance of the varistor, the total area of electrodes must be greatly decreased or the number of particle boundaries must be increased by increasing the thickness of the device between the electrodes.
		If the varistor voltage is decreased, the capacitance of the varistor is further increased, and therefore, it has been difficult to make the low voltage and the low capacitance requirements compatible with each other.
		As a characteristic of the varistor having such a structure, it is possible to form various shapes, and it is possible to use it as a protecting device from static electricity.
	www.patentstorm.us /patents/6507077.html (3301 words)

	Varistor: Definition and Links by Encyclopedian.com - All about Varistor (Site not responding. Last check: 2007-09-17)
		A varistor is an electronic component designed to protect circuits against excessive voltage.
		Varistors have a capacitance and could be called capacitors; likewise, all capacitors have a breakdown voltage.
		Varistors on the other hand are designed to repeatedly withstand breakdown.
	www.encyclopedian.com /va/Varistor.html (170 words)

	Varistor - Patent 4527146
		The varistor according to claim 1, wherein said sintered body is the product of a process consisting essentially of the steps of (a) preparing a homogeneous mixture comprising said principal constituent and said auxiliary constituents and (b) sintering said mixture.
		When a varistor is used for a device such as a lightening arrester, designed for the purpose of absorbing a large surge, it is required for it to have good capability of energy dissipation.
		Accordingly, the varistor of this invention is useful in a lighting arrester as a surge absorber for the direct current high voltage transmission.
	www.freepatentsonline.com /4527146.html (4790 words)

	Varistors: Ideal Solution to Surge Protection
		However, if the varistor is expected to protect against transients originating from external sources, the magnitude of the transient is typically unknown and an approximation technique must be applied.
		Without varistor protection, an initial current of 1A will flow through the thyristor bridge when S is opened, and a voltage sufficient to damage or destroy the thyristors will be developed.
		Of this 200 mJ, 15.1 mJ is dissipated in the heater, and 184.3 mJ is dissipated in the varistor.
	powerelectronics.com /mag/power_varistors_ideal_solution/index.html (2167 words)

	Metal Oxide Varistor (Site not responding. Last check: 2007-09-17)
		The metal oxide disks used in the varistors are essentially the same as those used in the high voltage station class arresters manufactured by GE.
		The varistor units have been successfully pressure relief tested with a system available short circuit current of at least 65,000 amperes rms.
		The varistor construction is uniquely designed and patented by GE to withstand this rigorous fault duty testing.
	www.ece.umr.edu /links/power/Energy_Course/energy/Electric_Trans/Series_comp/met_ox.html (418 words)

	Press Release [TDK Develops Low Capacitance, Low Clamping Voltage Multilayer Chip Varistor] (Site not responding. Last check: 2007-09-17)
		When the voltage impressed on multilayer chip varistors reaches a certain degree, current, which previously could not pass through, is suddenly able to pass, and they exhibit excellent inhibitive power against surges.
		Although earlier multilayer chip varistors were effective in protecting devices from surges, it has been difficult to maintain the deterrent force while decreasing the capacitance, and they present the drawback of causing deterioration to high-speed transmission signals.
		When the capacitance of multilayer chip varistors is decreased, as the terminal surface area becomes smaller, the resistance to surges declines and the clamping voltage increases, posing significant technological hurdles.
	www.tdk.co.jp /teaah01/aah11700.htm (567 words)

	The Varistor (Site not responding. Last check: 2007-09-17)
		The varistor is a surge protection device that is connected directly across the AC input.
		When a power surge or voltage spike is sensed, the varistor's resistance rapidly decreases, creating an instant shunt path for the over-voltage, thereby saving the sensitive control panel components (hopefully).
		Because the shunt path creates a short circuit, the varistor and the line fuse are subject to be damaged or weakened in the process.
	www.gallawa.com /microtech/varistor.html (253 words)

	Metal Oxide Varistors
		A test current of 1mA DC is typically used to determine varistor voltage classification type.
		Varistor voltage clamping characteristics can be defined at various test levels.
		Maximum surge current, 8/20µs waveform which a varistor is rated to withstand for a single surge.
	home.fuse.net /engineering/MOVDefinition.htm (177 words)

	Electrical component having high strength given stressing due to temperature change and due to surge currents, ...
		At their opposite end faces, the ceramic bodies of these components comprise electrodes, usually composed of screen printed silver paste which are applied to the ceramic body in a known manner after it is manufactured and which are heated later at temperatures of between 600.degree.
		The object of the present invention is to provide an electrical component of the type initially set forth, particularly a varistor, which is provided with power supply elements that guarantee a high resistance to thermal cycling as well as to stresses due to surge currents.
		Given a 60 mm diameter of a circular wafer of a varistor, given a thickness of 1.2 mm, a radius of the metallic coating R.sub.a of 28.62 mm the metal-free edge between the outer circumference of the metallic coating and the circumferential surface of the wafer is 1.38 mm wide.
	www.freepatentsonline.com /4714910.html (1419 words)

	STMicroelectronics \| TRANSIENT PROTECTION SOLUTIONS: Transil™ diode versus Varistor
		The first remark we can do, regarding these curves, is that the Varistor operates uniquely in bi-directional mode while the TransilTM diode can be both uni or bi-directional (here this is a unidirectional type).
		The second point is the leakage current which is higher for the Varistor particularly close to the knee of the curve.
		Tests were performed with 10A peak current, in such a condition the Varistor clamps at 37.2V while remaining voltage across the TransilTM in the same condition is only 24.6V.
	www.st.com /stonline/books/ascii/docs/10111.htm (1637 words)

	TDK Begins Volume Production of Industry's First 0603 Type Multilayer Chip Varistor
		In response to smaller circuit boards, the new 0603 type multilayer chip varistors were downsized to have approximately 78% less volume (approximately one-fifth) and 64% less area (approximately one-third) than the earlier 1005 types (1.0 mm x 0.5 mm).
		When multilayer chip varistors are made smaller, the electrode area also becomes smaller, resulting in lower capacity to withstand surges, and as a result, it is necessary to make the varistor elements thinner to achieve the properties suitable for low voltage circuits, presenting a significant technological hurdle.
		The new varistors will be used in IC circuit power supplies, reset circuits, and input and output terminals to prevent malfunctions of mobile devices as well as damage from static electricity.
	www.wirelessdevnet.com /news/2003/209/news3.html (600 words)

	Surge Absorbers Introduction
		Varistor voltage is specified by the manufacturer at low current (ie, 0.1-1.0 mA).
		Varistors have a very fast response time (ie, 50 nsec.) and will clamp at rated voltage for low currents or short periods of time.
		However, as a power surge increases in either current or duration, the Varistor clamping voltage can rise to unsafe levels, ultimately failing when its maximum energy level is exceeded.
	www.comm-omni.com /okaya/ok3-1.htm (537 words)

	World Products Inc. \| Metal Oxide Varistors \| Definitions
		Varistor product design flexibility and quick design cycles in order to assist our customers with their most stringent varistor applications.
		Varistor Voltage: Test characteristic that is used to classify varistors by type.
		When determining if varistor is within afore mentioned criteria the same temperature must be observed as was used for initial Varistor Voltage measurements.
	www.worldproducts.com /MOVDefinitions.htm (719 words)

	(ET) Re: varistor (Site not responding. Last check: 2007-09-17)
		So that the varistor doesn't conduct under those conditions, the nominal voltage rating for the varistor can be around 70 volts.
		If the charger is on, but there is not a good connection to the batteries, and the field is actuated, the varistor can see full open circuit charger voltage, which may be 80 volts (guess) and burn out.
		The current the varistor sees is probably a couple of Amps, but should be of short duration - limited by the energy stored in the magnetic field in the motor.
	cosmos2.phy.tufts.edu /mhonarc/elec-trak/msg05149.html (220 words)

	TESCO Online - High Voltage Surge Suppression
		Procedure: Measurement of the nominal varistor voltage (the voltage across the metal oxide varistor with 1 mAdc through the device) identifies the voltage rating of the MOV used in each design.
		This parameter is measured according to the IEEE definition of varistor voltage (ANSI/IEEE C62.33-1982).
		After this surge, the varistor voltage may not change more than 10% from the initial value and the disconnecting device (i.e.
	www.tesco-online.com /products/se/guidelines.htm (717 words)

	A First-Principles Study of Interface Systems
		The non-linearity of the ZnO based varistors is connected to the properties of the grain boundaries in the materials.
		Simulations of the I-V characteristics indicate that disorder in the material degrades the non-linearity of the varistor.
		The occupation and depletion of this Bi-Bi state could then be responsible for the varistor effect observed in Bi-decorated grain boundaries.
	w3.rz-berlin.mpg.de /~johanc/WebThesis/WebThesis.html (452 words)

	High Speed: maintenance log
		A varistor has near infinite resistance in the face of small potentials, but when it hits its threshhold, it shorts.
		That means there can be up to 38.5V and the varistor can short at as little as 42.3, which is a safe margin; now, the new varistor could short at as little as 37.8, which is actually marginally overlapping.
		The new varistor is considerably larger physically so practically it should be able to handle higher amperage.
	www.psaux.com /arcade/highspeed/maint.html (2498 words)

	K7 - Homepage of the Department for Nanostructured Materials (Site not responding. Last check: 2007-09-17)
		Owing to their exceptional non-linear current-voltage characteristics and energy absorption capability, varistors based on zinc oxide (ZnO) ceramics doped with small amounts of Bi, Sb, Mn, Co, Cr, NiO, and others, are extensively used for over-voltage protection.
		The performance of a varistor ceramic is closely related to its microstructure.
		In the previous year the results of these studies were used for the enhancement of the low-voltage varistors, the miniaturization of medium-voltage energy varistors by a reduction of their thickness, and the development of miniaturized high-voltage varistor blocks as elements for surge arresters.
	nano.ijs.si /e5.htm (241 words)

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