SIOV_General from EPCOS

SIOV metal oxide varistors
General technical information

Date:

December 2007

Data Sheet

? EPCOS AG 2008. Reproduction, publication and dissemination of this publication, enclosures hereto and the information contained therein without EPCOS’ prior express consent is prohibited.

General technical information

1 1.1

General technical information Introduction

Despite its many benefits, one of the few drawbacks of semiconductor technology is the vulnerability of solid-state devices to overvoltages. Even voltage pulses of very low energy can produce interference and damage, sometimes with far-reaching consequences. So, as electronics makes its way into more and more applications, optimum overvoltage or transient suppression becomes a design factor of decisive importance. SIOV? varistors have proven to be excellent protective devices because of their application flexibility and high reliability. The metal oxide varistor, with its extremely attractive price/performance ratio, is an ideal component for limiting surge voltage and current as well as for absorbing energy. The EPCOS product range includes radial-leaded disks, block varistors and strap varistors for power distribution applications. Special types for automotive electrical systems and for telecom applications round off the product range. Overvoltage protection devices like SIOV varistors are often referred to in international publications as a TVSS (transient voltage surge suppressor). 1.2 Definition

Varistors (variable resistors) are voltage-dependent resistors with a symmetrical V/I characteristic curve (figure 2) whose resistance decreases with increasing voltage. Connected in parallel with the electronic device or circuit that is to be guarded, they form a low-resistance shunt when voltage increases and thus prevent any further rise in the overvoltage.
Protection level

1400 V 1000 600

VAR

200

10

30

50 kA 70 Surge current

_ 70
VAR0017-R

_ 50

_ 30

_ 10

_ 200 _ 600 _ 1000 _ 1400

Max. permissible operating voltage

VAR0240-G-E

Figure 1

Circuit diagram symbol for a varistor

Figure 2

Typical V/I characteristic curve of a metal oxide varistor on a linear scale, using the SIOV-B60K250 as an example

? Registered trademark for EPCOS metal oxide varistors

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The voltage dependence of varistors or VDRs (voltage dependent resistors) may be approximately characterized by the formula I = K · Vα, where α denotes the “nonlinearity” exponent and in this way may be interpreted as a measure of the “steepness” of the V/I characteristic (more details will follow in section 1.6). In metal oxide varistors it has been possible to produce α figures of more than 30. This puts their protection levels in the same region as those of zener diodes and suppressor diodes. Exceptional current handling capability combined with response times of < 25 ns make them an almost perfect protective device. The principle of overvoltage protection by varistors is explained in chapter “Selection procedure” in section 1.2. 1.3 Microstructure and conduction mechanism

Sintering zinc oxide together with other metal oxide additives under specific conditions produces a polycrystalline ceramic whose resistance exhibits a pronounced dependence on voltage. This phenomenon is called the varistor effect. Figure 3 shows the conduction mechanism in a varistor element in simplified form. The zinc oxide grains themselves are highly conductive, while the intergranular boundary formed of other oxides is highly resistive. Only at those points where zinc oxide grains meet does sintering produce “microvaristors”, comparable to symmetrical zener diodes (protection level approx. 3.5 V). The electrical behavior of the metal oxide varistor, as indicated by figure 3, results from the number of microvaristors connected in series or in parallel. This implies that the electrical properties are controlled by the physical dimensions of the varistor:
■ Twice the ceramic thickness produces twice the protection level because then twice the number

of microvaristors are arranged in series.
■ Twice the area produces twice the current handling capability because then twice the number of

current paths are arranged in parallel.
■ Twice the volume produces almost twice the energy absorption capability because then there are

twice as many absorbers in the form of zinc oxide grains. The series and parallel connection of the individual microvaristors in the sintered body of a SIOV also explains its high electrical load capacity compared to semiconductors. While the power in semiconductors is dissipated almost entirely in one thin p-n junction area, in a SIOV it is distributed over all the microvaristors, i.e. uniformly throughout the component’s volume. Each microvaristor is provided with energy absorbers in the form of zinc oxide grains with optimum thermal contact. This permits high absorption of energy and thus exceptionally high surge current handling capability.
V 3.5 V 100 ?A I

Microvaristor Zinc oxide Intergranular boundary 10 to 50 ?m
VAR0389-I

Figure 3

Conduction mechanism in a varistor element 3 11/07

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General technical information

Grain size For matching very different levels of protection to ceramic thicknesses that are suitable for fabrication, SIOV varistors have to be produced from ceramics with different voltage gradients. The variation of raw materials and sintering process influence the growth of grain size (grain diameter approx. 10 to 100 ?m) and thus produce the required specific ceramic voltage (approx. 30 to 250 V/mm). The V/I characteristic of the individual microvaristors is not affected by this. Ceramics with a small specific voltage (low-voltage types ≤ 40 V) cannot handle the same current density as high-voltage types. That explains the differences in surge current, energy absorption and mechanical dimensions within the various type series. The effect of the different grain sizes is most apparent between the voltage classes K40 and K50. For example, the maximum permissible surge current is: SIOV-S07K40 SIOV-S07K50 1.4 imax = 250 A imax = 1200 A

Construction

Sintered metal oxide ceramics are processed on different production lines: Disk types Here the varistor disk is fitted with leads of tinned copper wire and then the ceramic body is coated with epoxy resin in a fluidized bed. Disk varistors in housing Here the disk varistors are fitted into a housing for special overvoltage fields application.
■ ThermoFuse (ETFV) types

These are designed for self-protection under abnormal overvoltage conditions. ■ Fail-safe (SFS) types No flame or rupture under specified test conditions (see “Reliability data”, “Overvoltage test” in the data sheet). Block types The large electromagnetic forces involved in handling currents between 10 kA and 100 kA call for solid contacting with special electrodes and potting in a plastic housing. Block varistors are electrically and mechanically connected by screw terminals. Strap types After contacting of the varistor ceramics with special bolt-holed electrodes, these components are coated with epoxy resin in a fluidized bed. For photos of all constructions see “Overview of types”.

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General technical information

1.5

Equivalent circuits

Figure 4 shows the simplified equivalent circuit of a metal oxide varistor. From this the behavior of the varistor can be interpreted for different current ranges. Leakage current region (< 10–4 A) In the leakage current region the resistance of an ideal varistor goes towards ∞, so it can be ignored as the resistance of the intergranular boundary will predominate. Therefore RB << RIG. This produces the equivalent circuit in figure 5: The ohmic resistance RIG determines behavior at low currents, the V/I curve goes from exponential to linear (downturn region). RIG shows a distinct temperature dependence, so a marked increase in leakage current must be expected as temperature increases. Normal operating region (10–5 to 103 A) With RV << RIG and RB << RV, RV determines the electrical behavior (figure 6). The V/I curve (figure 12) follows to a good approximation the simple mathematical description by an exponential function (equation 3 in 1.6.1) where α > 30, i.e. the curve appears more or less as a straight line on a log-log scale. High-current region (> 103 A) Here the resistance of the ideal varistor approaches zero. This means that RV << RIG and RV < RB (figure 7). The ohmic bulk resistance of ZnO causes the V/I curve to resume a linear characteristic (upturn region). Capacitance Equivalent circuits 4 and 5 indicate the capacitance of metal oxide varistors (see product specifications for typical values). In terms of overvoltage suppression, a high capacitance is desirable because, with its lowpass characteristic, it smooths steep surge voltage edges and consequently improves the protection level. Lead inductance The response time of the actual varistor ceramics is in the picosecond region. In the case of leaded varistors, the inductance of the connecting leads causes the response time to increase to values of several nanoseconds. For this reason, all attempts must be made to achieve a mounting method with the lowest possible inductance i.e. shortest possible leads.

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General technical information

Equivalent circuits

L

L
C R IG R VAR

RB
VAR0118-6

C

R IG
VAR0119-E

Figure 4

Figure 5

L

L
C R VAR
VAR0120-H

RB
VAR0121-Q

Figure 6

Figure 7

L C RIG RVAR RB

Lead inductance (≈ 1 nH/mm) Capacitance Resistance of intergranular boundary (ρ ≈ 1012 to 1013 ?cm) Ideal varistor (0 to ∞ ?) Bulk resistance of ZnO (ρ ≈ 1 to 10 ?cm)

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General technical information

1.6 1.6.1

V/I characteristics Forms of presentation

The V/I characteristics of metal oxide varistors are similar to those of power functions (odd exponents), so it is fairly obvious that the latter should be used to describe them. As the curves are symmetrical, only one quadrant is generally shown for reasons of simplification (figure 8): I = KV I K V α
α

α>1

(equ. 1)

Current through varistor Ceramic constant (depending on varistor type) Voltage across varistor Nonlinearity exponent (measure of nonlinearity of curve)

Another possible interpretation of the physical principle underlying these curves is that of a voltagedependent resistance value, and particularly its rapid change at a predetermined voltage. This phenomenon is the basis of the varistor protection principle (figure 9): 1 1–α V -V R = V --- = ------------ = --α K I KV (equ. 2)

Equations 1 and 2 can be shown particularly clearly on a log-log scale, because power functions then appear as straight lines: log I = log K + α log V 1? - + ( 1 – α ) log V log R = log ? --? K? (equ. 3) (equ. 4)

This is virtually the only form of presentation used for varistor characteristics (figures 10 and 11). A further advantage of the log-log format is the possibility of showing the wide range of the V/I curve (more than ten powers of 10). It is evident that the simplified equations 1 to 4 cannot cover the downturn and upturn regions as described in section 1.5. Here, a mathematical description as shown in equation 21 in chapter “Application notes” is required. Determining nonlinearity exponent α Two pairs of voltage/current values (V1/I1 and V2/I2) are read from the V/I characteristic of the varistor and inserted into equation 3, solved for α: log I 2 – log I 1 α = ----------------------------------log V 2 – log V 1 (equ. 5)

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General technical information

Presentation of the V/I characteristics

V

R

I
VAR0122-Y

V
VAR0123-7

Figure 8

Figure 9

log V

log R

log I
VAR0124-F

log V
VAR0125-N

Figure 10

Figure 11

1.6.2

Real V/I characteristic and ohmic resistance

Figure 12 shows a typical V/I characteristic with SIOV-B60K250 taken as an example . The downturn and upturn regions according to equivalent circuits 5 and 7 are easy to make out. Calculating nonlinearity exponent α Normally α is determined according to equation 5 from the pairs of values for 1 A and 1 mA of the V/I characteristic. For figure 12 this means: log I 2 – log I 1 3 log 1 – log 10–3 0 – ( –3 ) - ≈ 38 α = ----------------------------------- = ----------------------------- = ---------- = -----------------------------------------0.08 log 470 – log 390 2.67 – 2.59 log V 2 – log V 1 The V/I curve of figure 12 is virtually a straight line between 10–4 and 103 A, so it is described over a wide range to a good approximation by equation 3. The downturn and upturn regions may be adapted by inserting correction components in equation 3. Another type of characteristic curve approximation is described in chapter “Application notes”, section 1.9.1. Derived from figure 12, figure 13 shows the change in static resistance R = V/I for SIOV-B60K250. The resistance is > 1 M? in the range of the permissible operating voltage, whereas it can drop by as many as ten powers of 10 in case of overvoltage.
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General technical information

Figure 12

Real V/I characteristic of a metal oxide varistor as exemplified by SIOV-B60K250

1400 V 1200 1000

VAR0242-W-E

Protection level

800 600 400 Max. permissible operating voltage 200 0 _3 _ _ 10 10 2 10 1 10 0 10 1 10 2 10 3 10 4 10 5 10 6 10 7 10 8 Static resistance

?

10 10

Figure 13

Static resistance of a metal oxide varistor versus protection level as exemplified by SIOV-B60K250

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General technical information

1.6.3

Presentation of tolerance band

The real V/I characteristic of individual varistors is subject to a certain deviation, which is primarily due to minor fluctuations in manufacturing and assembly process parameters. For varistors belonging to a certain type, their V/I curves are required to lie entirely within a well defined tolerance band. The tolerance band shown in figure 14 illustrates this in the case of SIOV-S14K14. Varistors are operated at one of two conditions: If the circuit is operated at normal operating voltage, the varistor will be highly resistive. In an overvoltage event, it will be highly conductive. These conditions concern two different segments of the V/I curve: Lefthand part of curve (< 1 mA): This part of the curve refers to the “high-resistance” mode, where circuit designers may generally want to know about the largest possible leakage current at given operating voltage. Therefore the lower limit of the tolerance band is shown. Righthand part of the curve (> 1 mA): This segment covers the “low-resistance” mode in an overvoltage event, where the circuit designer’s primary concern is the worst-case voltage drop across the varistor. The upper limit of the tolerance band is shown. The 1 mA “dividing line” between the two segments does not really have any electrophysical significance but it is generally used as a standard reference (varistor voltage – refer to section 1.7.5 for explanations). Related branches are identified by the same maximum AC operating voltage (here “14”). V/I characteristic 1 in figure 14 shows the mean value of the tolerance band between the limits indicated by dashed lines. The mean at 1 mA represents the varistor voltage, in this case 22 V. The tolerance K ± 10% refers to this value, so at this point the tolerance band ranges from 19.8 to 24.2 V. Leakage current at operating voltage: A maximum permissibe operating voltage of 18 VDC is specified for SIOV-S14K14. For this, depending on where the varistor is in the tolerance band (figure 14), you can derive a leakage current between 6 · 10–6 A and 2 · 10–4 A (region 2). If the varistor is operated at a lower voltage, the figure for the maximum possible leakage current also drops (e.g. to max. 2 · 10–6 A at 10 VDC). In the worst case, the peak value of the maximum permissible AC operating voltage (v = 2 ? 14 V = 19.8 V) will result in an ohmic peak leakage current of 1 mA (see figure 14, point 3). Protection level: Assuming a surge current of 100 A, the voltage across SIOV-S14K14 will increase to between 35 V and 60 V (region 4), depending on where the varistor is in the tolerance band. 1.6.4 Overlapping V/I characteristics

As explained earlier (section 1.3) the differences in nonlinearity between voltage classes up to K40 and K50 and above lead to overlapping V/I curves. In particular with SIOV disk varistors, before selecting voltage rating K40 you should always check whether K50 is not a more favorable solution. Firstly, the protection level is lower for higher surge currents, and secondly, the load capability of K50 is considerably higher for varistors of the same diameter.

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General technical information

Figure 14

Tolerance limits of a metal oxide varistor as exemplified by SIOV-S14K14

Figure 15

Tolerance limits of a metal oxide varistor as exemplified by SIOV-S14K14

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General technical information

1.7 1.7.1

Terms and descriptions Operating voltage

The product tables specify maximum AC and DC operating voltages. These figures should only be exceeded by transients. Automotive types, however, are rated to withstand excessive voltage (jump start) for up to 5 minutes. The leakage current at specified operating voltage is negligible. The maximum permissible AC operating voltage is used to classify the individual voltage ratings within the type series. In most applications the operating voltage is a given parameter, so the varistors in the product tables are arranged according to maximum permissible operating voltage to facilitate comparison between the individual varistor sizes. 1.7.2 Surge current, transient

Short-term current flow – especially when caused by overvoltage – is referred to as surge current or transient. The maximum surge current that can be handled by a metal oxide varistor depends on amplitude, pulse duration and number of pulses applied over device lifetime. The ability of a varistor to withstand a single pulse of defined shape is characterized by the maximum non-repetitive surge current specified in the product tables (single pulse, tr ≤ 20 ?s). If pulses of longer duration or multiple pulses are applied, the surge current must be derated as described in section 1.8. Maximum surge current The maximum non-repetitive surge current is defined by an 8/20 ?s waveform (rise time 8 ?s/decay time to half value 20 ?s) according to IEC 60060 as shown in figure 16. This waveform approximates a rectangular wave of 20 ?s. The derating curves of the surge current, defined for rectangular waveforms, consequently show a knee between horizontal branch and slope at 20 ?s. 1.7.3 Energy absorption
0∫ t1

The energy absorption of a varistor is correlated with the surge current by W =
t

v ( t ) i ( t ) dt

(equ. 6)

where v (t) is the voltage drop across the varistor during current flow. Figure 13 in chapter “Application notes” illustrates the electrical performance for the absorption of 100 J in the case of SIOV-S20K14AUTO.

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General technical information

Maximum energy absorption Surge currents of relatively long duration are required for testing maximum energy absorption capability. A rectangular wave of 2 ms according to IEC 60060 (figure 17) is commonly used for this test. In the product tables the maximum energy absorption is consequently defined for a surge current of 2 ms. Ts Tr 01 Im Rise time in ?s Decay time to half value in ?s Nominal start Peak value

i

% 100 90 Leading edge 50

Peak

Trailing edge

Frequently used Ts /Tr ratios: Surge currents 4/10 ?s 8/20 ?s 10/350 ?s 10/1000 ?s Surge voltages 1.2/50 ?s 10/700 ?s

10 0

01

Ts Tr

Im

t
VAR0170-I-E

Figure 16

Waveform to IEC 60060 standard

% 100 90

B

B’

10 TD TT
VAR0171-R-E

Possible polarity reversal

TD TT Figure 17 Waveform to IEC 60060 standard 13 11/07

Duration of peak value (≈ 2 ms) Total duration

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General technical information

1.7.4

Average power dissipation

If metal oxide varistors are selected in terms of maximum permissible operating voltage, the resulting power dissipation will be negligible. However, the rated maximum power dissipation must be taken into account if the varistor has not enough time to cool down between a number of pulses occurring within a specified isolated time period. The examples in chapter “Calculation examples” show the calculation of the minimum time interval in periodic application of energy. 1.7.5 Varistor voltage

The varistor voltage is the voltage drop across the varistor when a current of 1 mA is applied to the device. It has no particular electrophysical significance but is often used as a practical standard reference in specifying varistors. 1.7.6 Tolerance

Tolerance figures refer to the varistor voltage at 25 °C. As shown in figure 14 the tolerance band for other current values can be larger. Note: When the tolerance is examined, the current of 1 mA must only be applied briefly so that the results are not corrupted by warming of the varistor (see temperature coefficient). The current should only flow for 0.2 up to 2.0 s, typical is a duration of 1 s. 1.7.7 Protection level (clamping voltage)

The protection level is the voltage drop across the varistor for surge currents > 1 mA. The V/I characteristics show the maximum protection level as a function of surge current (8/20 ?s waveform). In the product tables the protection level for surge currents according to the R10 series (ISO 497) is additionally specified. This is also referred to as clamping voltage. 1.7.8 Capacitance

The product tables specify typical capacitance figures for 1 kHz. The tabulated values show that metal oxide varistors behave like capacitors with a ZnO dielectric. The capacitance rises in proportion to disk area (and thus to current handling capability) and drops in proportion to the spacing of the electrodes, i.e. it decreases with increasing protection level. Capacitance values are not subject to outgoing inspection. 1.7.9 Response behavior, response time

The response time of metal oxide varistor ceramics to transients is in the subnanosecond region, i.e. varistors are fast enough to handle even ESD transients with the extreme steep current rise of up to 50 A/ns. You can find similar results for the silicon chip used in semiconductor protective devices like suppressor diodes.

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General technical information

However, when the chip is mounted in its package, the response time increases due to the series inductance of its package to values > 1 ns. The varistors specified in this data book have response times <25 ns. Comparing the protection behavior of varistors with semiconductors, higher figures of protection level may be found for varistors. This cannot be explained by a higher response time of varistors – which definitely is not true – but rather it is due to slightly less nonlinearity of the V/I characteristics. The V/I characteristics in this data book have been measured at currents > 1 mA with the standard 8/20 ?s waveform (figure 16). So they allow for the inductive voltage drop across the varistor for the particular di/dt. If surge currents with steep edges are to be handled, one should always design the circuit layout for as low an inductance as possible. 1.7.10 Temperature coefficient Metal oxide varistors show a negative temperature coefficient of voltage. Figure 18 shows the typical varistor behavior. The temperature coefficient value drops markedly with rising currents and is completely negligible from roughly 1 mA upwards.
100 VV % 70 50 40 30 20
VAR03650

_ 10 ?C
25 ?C 50 ?C 85 ?C 125 ?C

10 _ 10 9

10

_8

10

_7

10

_6

10

_5

10

_4

A 10

_3

i

Figure 18

Typical temperature dependence of the V/I characteristic taking SIOV-S20K275 as an example. (VV = applied DC voltage in percentage of varistor voltage at +25 °C)

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An increase in leakage current is consequently noticeable at higher temperatures, especially in the ?A region. Equation 7 describes the TC of varistor voltage (at 1 mA): TC < 0.5 ? 10 /K = 0.05% /K = 1%/ ? 20 K
–3

(equ. 7)

Figure 19 shows results for SIOV-S20K275 as an example.
3 % 2 1 0

_ 0.5 . 10 _ 3/K

?V/ V20

_1 _2 _3 _4 _5
Figure 19

_ 40

20

80

?C

140

VAR0126-W

Temperature coefficient of voltage at 1 mA for SIOV-S20K275

1.8

Derating

Derating is the intentional reduction of maximum ratings in the application of a device. With metal oxide varistors derating is of particular interest under the following conditions:
■ Derating for repetitive surge current and energy absorption ■ Derating at increased operating temperatures

1.8.1

Derating for repetitive surge current

A typical feature of metal oxide varistors is the dependence of the maximum permissible ratings for surge current, and thus for energy absorption, on the pulse shape, pulse duration, and the number of times this load is repeated during the overall lifetime of the varistor. The derating for a particular maximum permissible surge current can be derived from the curves for a type series in repetition figures graded 10x. The surge derating curve is mainly dependent on the varistor size but also voltage rating. Such derating curves can be found for all individual varistors in this data book. The maximum permissible energy absorption can also be calculated from the derating curves by Wmax = vmax imax tr max

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General technical information

1.8.2

Derating at increased operating temperatures

For operating temperatures exceeding 85 °C or 125 °C the following operating conditions of varistors have to be derated according to figure 20:
■ ■ ■ ■

Voltage Surge current Energy absorption Average power dissipation Operating and storage temperature

1.9

The upper limits of the operating and storage temperature ranges for the individual type series can be deduced from the 100 % and 0 % values in figure 20, respectively. For lower ratings, refer to the product tables. 1.10 Climatic categories

The limit temperatures according to IEC 60068 are stated in the product tables as LCT (lower category temperature) and UCT (upper category temperature).
110 % 90 80
VAR0632-N-E

Permissible percentage of max. ratings

70 60 50 40 30 20 10 0 60 70 80 90 100 110 120 130 140 ?C 150 TA 1 2 3

Derating curve 1 SIOVB LS

Derating curve 2 SIOVS…(AUTO)(E2)(E3) Q ETFV types SFS types

Derating curve 3 SIOVS…AUTOD1

Figure 20

Temperature derating for operating voltage, surge current, energy absorption and average power dissipation

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General technical information

1.11

Overload response

1.11.1 Moderate overload Surge currents or continuous overload of up to approx. one and a half times the specified figures can lead to a change in varistor voltage by more than ±10%. In most cases the varistor will not be destroyed, but there may be an irreversible change in its electrical properties. The thermal fuse in EPCOS ETFV may open in such a condition. 1.11.2 Heavy overload Surge currents far beyond the specified ratings will puncture the varistor element. In extreme cases the varistor will burst. Excessive steady-state overload fuses the ZnO grains and conducting paths are formed with the bulk resistance of ZnO, which is considerably lower than the resistance of the original varistor. The overload can overheat the varistor ceramic with the result that it becomes unsoldered from the electrodes. 1.12 Design notes

If steep surge current edges are to be expected, you must make sure that your design is as lowinductive as possible (cf 1.7.9). 1.12.1 Physical protection, fuses Due to the unpredictable nature of transients a varistor may be overloaded although it was carefully selected. Overload may result in package rupture and expulsion of hot material. For this reason the varistor should be physically shielded from adjacent components, e.g. by a suitable metal case. Fuse protection of varistors against excessive surge current is usually not possible because standard fuses are unable to quench surge currents. But fuses can offer protection against damage caused by follow-on currents. Such follow-on currents flow when a damaged varistor is in lowresistance mode and still connected to power. When varistors are operated on standard line impedances, nominal fuse currents and varistor type series should be matched as follows: Type Nominal fuse current [A] S05 ≤1 S07 ≤3 S10 ≤6 S14/ SFS14 ≤10 S20/ Q14 ≤16 S25/ Q20 ≤ 25

Type Nominal fuse current [A]

ETFV14 ≤10

ETFV20 ≤16

ETFV25 ≤ 25

Type Nominal fuse current [A]

B32 ≤ 50

B40/LS40/ LS41/LS42 ≤ 80

B60/LS50 ≤125

B80 ≤160

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In applications where the conditions deviate from standard power line impedances, better fuse protection of the varistor can be obtained using thermo-fuses. These thermo-fuses should be in direct thermal contact with the varistor. Better protection can be achieved with a thermal fuse or EPCOS ThermoFuse varistors series ETFV where the thermal coupling is matched with the varistors. 1.12.2 Potting and sealing, adhesion Potting, sealing or adhesive compounds can produce chemical reactions in the varistor ceramic that will degrade its electrical characteristics. Information about this is available on inquiry. 1.12.3 Prior damage The values specified only apply to varistors that have not been subjected to prior electrical, mechanical or thermal damage. 1.12.4 Environmental conditions SIOV varistors are designed for indoor applications. On all accounts, prevent exposure to:
■ ■ ■ ■ ■

Direct sunlight Rain or condensation Steam, saline spray Corrosive gases Atmospheres with reduced oxygen content

1.12.5 Mechanical strength of wire leads of disk-type varistors The wire leads comply with the requirements of IEC 60068-2-2. They may only be bent at a minimum distance of 4 mm from the enamel coating end. When bending leads to shape, the lead-component junction must be supported. The minimum bend radius should be 0.75 mm. 1.13 Designation system variable resistor registered tradename for EPCOS varistors

Varistor = SIOV ? = Table 1 SIOV

Design

Rated dimension

Tolerance

Max. AC oper. volt.

Additional specifications

Additional specifications

Design

B ETFV LS … P LS … PK2 LS … QP LS … QPK2 Q S SFS

Block type (HighE series) Disk type in housing (ThermoFuse) Strap type, round, epoxy coating, bent straps (HighE series) Strap type, round, epoxy coating, straight straps (HighE series) Strap type, square, epoxy coating, bent straps (HighE series) Strap type, square, epoxy coating, straight straps (HighE series) Disk type, square, leaded (EnergetiQ series) Disk type, round, leaded Disk type in housing

Rated diameters/length of disk varistors 5 up to 80 mm.
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Table 1 (continued) Tolerance of K varistor voltage L (1 mA) M S…A/B/C Max. permissible AC operating voltage Taping ±10% ±15% ± 20% Special tolerance A, B or C

11 … 1100 VRMS,max

G GA G.S. AUTO AUTO … D1 E2 E3 E4 K2 M P Q R5 R7

Tape / reel Tape / Ammo pack Tape / reel, crimp style S, S2, S3, S4, S5 (see chapter “Taping, packaging and lead configuration”) Additional load dump and jump start specification Additional load dump, jump start and high-temperature specification AdvanceD series SuperioR series SuperioR series Suffix to define modifications Customer specific trimmed lead length (in mm) Standard coating (epoxy) Square shape = = 5.0 7.5 Lead spacing differs from standard Lead spacing differs from standard

Appendix

Production code: all coated varistors are marked with year/week code. Example: 07 09 = 9th week of year 2007 Abbreviations for metal oxide varistors: MOV ZnO VDR metal oxide varistor zinc oxide varistor voltage-dependent resistor

Abbreviation for overvoltage protection elements in general: TVSS transient voltage surge suppressor

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General technical information

1.14

Marking of disk varistors

Disk-type varistors have printed markings as shown in figure 21. They are distinguished as follows: no underline under the “S” (Standard), an additional underline under the S… (for type series AdvanceD, E2) or a line above the S… (for type series SuperioR, E3) or a line above and under the S… (for SuperioR types, E4). The lower section of the marking area contains the date code yy ww.

S20 K275 07 22

S20 K275 07 22

S20 K275 07 22

S25 K275 07 22

StandarD

AdvanceD, E2

SuperioR, E3

SuperioR, E4
VAR0366-W

Figure 21

Various forms of printed markings of disk-type varistor series StandarD, AdvanceD and SuperioR, using S20K275 as an example. Date code 07 09 = ? yy ww = ? 9th week of year 2007

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General Secure Multi-Party Computation from any Linear Secret-Sharing Scheme
News from the Frontier of Public Administration The Swedish Director-General Speaking. Pape
A general framework for tree segmentation reconstruction from medical volume
Wang - From General System Theory To Total Quality Management (2004, 8p)
From the Divisions of General
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