307C OVERCURRENT THERMISTORS - Vishay Telefunken

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307C Overcurrent Thermistors

Vishay Cera-Mite

Document Number: 23089

Revision 14-May-02 ceramite.support@vishay.com

PTCR Overcurrent Protection

FEATURES:

Sizes For Your Application - Hold currents from 5 mA to 1.5 A are available

in sizes from 4 to 22mm.

Better Protection, Maintenance Free - PTCRs reset after an overcurrent

situation. Protection levels may be set lower than possible with fuses, without

worrying about nuisance trips.

Resetting, Non Cycling - Functioning as a manual reset device, PTCR

overcurrent protectors remain latched in the tripped state and automatically

reset only after voltage has been removed. This prevents continuous cycling,

and protects against reclosing into a fault condition.

Simplified Mounting - PTCRs may be mounted directly inside end use

equipment. Unlike fuses, no bulky fuseholder or access for user replacement

is required.

Ceramic Material Selection - Various curie materials are available to tailor

hold and trip current operating points.

Repeatable, No Hysteresis - After resetting, ceramic PTCRs return to the

initial resistance value, providing repeatable, consistent protection levels.

Unlike polymer type PTCRs, Vishay Cera-Mite devices exhibit no resistance

hysteresis application problems.

Telecom Line Balance - In telecom circuits matched pairs are used to

maintain line balance. Unlike polymer PTCRs, ceramic devices maintain

balance after resetting.

A NEW DIMENSION

The Positive Temperature Coefficient

Resistor’s (PTC thermistor) unique property

of dramatically increasing its resistance

above the curie temperature makes it

an excellent candidate for overcurrent

protection applications. Overcurrent

situations in electronic devices occur

due to voltage fluctuations, changes in

load impedance, or problems with system

wiring. PTC thermistors monitor current in

series connected loads, trip in the event

of excess current, and reset after the

overload situation is removed, creating a

new dimension of flexibility for designers.

APPLICATIONS:

• Telecommunication Products

• Electronic Power Supplies

• Automotive Motor Protection

• Industrial Control Systems

In a typical current limiter application, the PTC device is connected in series

with a load impedance (Fig P-1). When current (I) flows, internal I2R losses

attempt to increase the PTCR’s temperature. To maintain the low resistance

“on” state, stabilization must occur below the switching temperature, where

the heat generated (I2R) is balanced by heat lost due to radiation and

conduction.

Hold current (IH) is the maximum continuous current at which a PTCR can

be maintained in a low resistance “on” state while operating at rated ambient

temperature (typ 25°C). To prevent nuisance tripping, choose the rated hold

current to be greater than the normal current expected.

Since heat dissipated by the device is proportional to the ambient temperature,

hold current must be derated for ambients higher than 25°C according to

the following relationship:

Hold Current (IH) = D(TSW - TA)

PTC

Where:

D = Dissipation Constant

(varies based on disc

size, wire type, &

coating material)

SW = Switching (Curie)

Temperature of

PTCR Material

A = Ambient Temperature

PTC= Resistance of PTCR

at 25°C

Fig P-1

Typical PTC Current Limiter Application

This relationship is shown in Fig P-2,

which provides hold current (IH) derating

estimates for ambient temperatures in

excess of 25°C. Five curie materials

illustrate the design flexibility offered by

ceramic PTCR’s.

Fig P-2

PTC Thermistor Overcurrent Protectors

Ambient Temperature Derating of Hold and

Trip Currents

LOAD

PTC

Ambient Temperature (°C)

-10 0 10 20 30 40 50 60 70 80 90 100 110 120

70°C Curie Material

80°C Curie Material

90°C Curie Material

105°C Curie Material

120°C Curie Material

Percent Derating

140%

120%

100%

80%

60%

40%

20%

APPLICATION DATA

Document Number: 23089

Revision 14-May-02

www.vishay.com

307C Overcurrent Thermistors

Vishay Cera-Mite

ceramite.support@vishay.com

How Various Physical Parameters Influence a PTCs:

PARAMETER VOLTAGE & CURRENT CAPABILITY HOLD CURRENT & TRIP TIME

Disc Diameter (D) Increased diameter will increase voltage Increased diameter will increase

and current ratings. hold current and lengthen trip time.

Disc Thickness (T) Increased thickness will increase Increased thickness will increase

voltage rating; may or may not hold current and lengthen trip time.

increase current rating.

Curie (Switch) (T

) Typically, lower switch temperature Higher switch temperature

Temperature materials have higher voltage/ materials increase hold current

current capability. and lengthen trip time.

Resistance (R25) Higher resistance will increase Lower resistance will increase hold

voltage capability. current and lengthen trip times.

Thermal Loading Increased thermal loading typically Increased thermal loading increases

(Heat Sink) reduces the maximum interrupting current. hold current and lengthens trip times.

Wire Leads Wire leads added to a PTCR pellet act as Depends on thermal conductivity of

a thermal load resulting in reduced wire used. Copper will increase

maximum interrupting current. hold current and trip time.

Coating Material Applying coating to a leaded PTCR has Applying coating to a leaded PTCR

minimal effect on voltage/current ratings. increases hold current/trip time 10-20%.

APPLICATION DATA

TRIPPING ACTION DUE TO OVERCURRENT

During normal operation, the PTCR remains in a low base

resistance state (Fig P-3, Region 1). However, if current

in excess of hold current (IH) is conducted, I2R losses

produce internal self heating. If the magnitude and time of

the overcurrent event develops an energy input in excess of

the device’s ability to dissipate heat, the PTCR temperature

will increase, thus reducing the current and protecting the

circuit.

PTC current limiters are intended for service on telecom

systems, automobiles, or the secondary of control transform-

ers or in similar applications where energy available is limited

by source impedance. They are not intended for application

on AC line voltages where source energy may be high and

source impedance low.

The current required to trip (IT) is typically specified as two

times the hold current (2 x IH). IT is defined as the minimum

rms conduction current required to guarantee thermistor

switching into a high resistance state (Fig P-3, Region 2) at

a 25°C ambient temperature.

Ambient temperature influences the ability of the PTCR to

transfer heat via surface radiation and thermal conduction at

the wire leads. At high ambient temperatures, less energy

input (via I2R) is required to reach the trip temperature. Low

ambients require greater energy input. Approximate derating

effects are shown in Fig P-2.

Since the tripping operation is due to thermal change, there

is a time-trip curve associated with each device. At relatively

low magnitudes of overcurrent, it may take minutes for the

device to trip. Higher current levels can result in millisecond

response time. Trip time (t) can be calculated as follows

kM(TSW -T

Trip Time (t) = I 2R - D(TSW-T

Where: k = coefficient of heat absorption = 0.603 J/g/°C

M = mass of PTCR = volume x 5.27x10 -3g/mm3

R = zero power resistance of PTCR at 25°C

Fig P-3

CERAMIC MATERIALS

The temperature at which the PTCR changes from the

base resistance to high resistance region is determined by

the PTCR ceramic material. Switching temperature (TSW)

described by the boundary between regions 1 & 2 (Fig P-3),

is the temperature point at which the PTCR has increased

to two times its base resistance at 25°C ambient (RSW = 2

x R25). Design flexibility is enhanced by Cera-Mite’s wide

selection of ceramic PTCR materials with different switching

temperatures (Fig P-4).

Fig P-4

Table 2

SELF RESETTING - NON CYCLING - REPEATABLE

After tripping, the PTCR will remain latched in its high

resistance state as long as voltage remains applied and

sufficient trickle current is maintained to keep the device

above the switching temperature. After voltage is removed,

the PTCR resets (cools) back to its low resistance state and

is again ready to provide protection.

PHYSICAL DESIGN CONSIDERATIONS

Diameter (D) - Common diameters range from 4 to 22mm.

Thickness (T) - Typical thickness ranges from 1 to 5mm.

Curie (Switching) Temperature (TSW) - See Fig P-4.

Resistivity (ρ) -

Determined during sintering process; combined

with pellet geometry results in final resistance

based on:

R25 = zero power resistance at 25°C = ρT

Area

PTCR Overcurrent Protection

Vishay Cera-Mite offers

a wide selection of

ceramic PTC materials

providing flexibility for

different ambient

temperatures. Close

protection levels are

possible by designing

resistance and physical

size to meet specific

hold current and trip

current requirements.

Curie Temperature °C (±5°)

Resistance Ratio

100K

10K

100

2.0

1.0

0.1

55°C

70°C

80°C

90°C

105°C

120°C

PTC

RESISTANCE

REGION 2

HIGH

RESISTANCE

REGION 1

BASE

RESISTANCE

R vs. T Operating Characteristics

PTC

Temperature

TSW

25°C

R25

RSW =

2 x R25

100

1000

10000

100000

Resistance (log scale)

www.vishay.com

307C Overcurrent Thermistors

Vishay Cera-Mite

Document Number: 23089

Revision 14-May-02 ceramite.support@vishay.com

PTCR Overcurrent Protection

VISHAY

HOLD (IH) TRIP (IT) RESISTANCE SWITCH SIZE (D) CERA-MITE

CURRENT CURRENT R25 TEMP. NOMINAL PART

mA mA Ohms °C mm NUMBER

110 220 30 105 6.5 307C1127

100 200 15 70 8 307C1128

100 200 20 80 8 307C1126

110 220 18 80 8 307C1268

120 240 15 80 8 307C1129

140 280 15 105 8 307C1435

110 220 15 70 9.5 307C1134

130 260 15 80 9.5 307C1130

140 280 9 70 9.5 307C1436

150 300 10 80 9.5 307C1437

Note 1 Note 2 Note 3

Fig P-5 Fig P-6 PTC THERMISTORS FOR

TELECOMMUNICATIONS

PTC Thermistors provide protection

for large digital switches. Vishay Cera-

Mite has pioneered this field with

ceramic PTC thermistors working

closely with major telephone equip-

ment and telephone protection

manufacturers. The requirements are

dynamic, as switch makers continually

strive to protect at lower levels. Vishay

Cera-Mite participates with industry

standard technical committees to

establish common definitions and

understanding of this new tech-

nology.

Over-voltage

Pressure

Contact

Line

Tip

C.O.

Tip Ground C.O. Ring

Over-Current

Pressure

Contact

PTCR

Main Switch

C.O. Ring

To Battery

PTCR

C.O. Tip

Leaded PTCR

PTCR

C.O. Tip

C.O. Ring

Line Ring

Line Tip

PTCR

PTC THERMISTOR PELLETS FOR TELECOMMUNICATIONS

Table 2

Fig P-7

Rated Voltage = 60 VDC

Rated Current = 3A

Maximum Voltage = 220 Vrms

Fig P-8

Time-Trip Curves for Popular Telecom Pellets

Note 1

Hold and trip currents

are specified at

25°C ambient.

Note 2

R25 is nominal zero power

resistance at 25°C with

tolerance of ± 20%.

Note 3

All pellets have silver elec-

trodes suitable for pressure

contact mounting.

INTERRUPTING CAPACITY ESTIMATES

Under unusual circumstances, telecommunication lines may

be subjected to high surge currents as might occur from

lightning effects or accidental crossing with power lines or

transformer primaries.

Fig P-10 shows trip time curves for higher currents. Estimated

interrupting capability data is also shown in Table 3 and

is expressed as “I2t Let Through” based on test data

conducted in accordance with UL 497A and CSA 22.2 No.

0.7-M1985.

The data shown is for reference. Specific short circuit data or

interrupting capability is partially determined by the mounting

means and circuit application.

Fig P-9

Fig P-10

Time VS. Current Curves for High Current Surges (25°C)

Base

Electrode

Silver

Electrode

Solid Ceramic

Disc

2.5mm

Current (Amperes)

Operating Time to 50% Current

0 .05 1 1.5 2 2.5 3

Time (Seconds)

307C1130

307C1129

307C1128

307C1126

307C1127

PTCR

Scope

Time To

RL 1/2

RSHUNT

50 - 100 mV

Current (Amperes)

2 4 6 8 10 12 14 16 18 20

10,000

1,000

100

Time (Milliseconds)

10 ohm, 80°C Pellets for

Diameters (mm

14.5mm

12.5mm

11.0mm

9.5mm

8.0mm

6.5mm

Variable

Voltage

Source

0-600V

60Hz

Current

Probe or

26 AWG

Pair

A = 1.5 sec.

B = 5 sec.

C = 30 min.

PTCR

Current

Limiter

275

Timed Interrupter

2 t Let Through

100

0.1

Document Number: 23089

Revision 14-May-02

www.vishay.com

307C Overcurrent Thermistors

Vishay Cera-Mite

ceramite.support@vishay.com

PTCR Overcurrent Protection

VISHAY

HOLD (IH) TRIP (IT) RESISTANCE SWITCH SIZE (D) MAX. CERA-MITE

CURRENT CURRENT R25 TOL. TEMP. NOMINAL VOLTAGE PART

mA mA Ohms % °C mm VRMS NUMBER

70 140 100 25 120 6.5 265 307C1418

100 200 20 20 80 8 220 307C1305

100 200 30 20 105 8 220 307C1506

110 220 18 20 80 8 220 307C1354

110 220 25 20 105 8 220 307C1514

120 240 15 20 80 8 220 307C1129

120 240 20 20 105 8 220 307C1296

120 240 25 20 120 8 220 307C1470

130 260 13 20 80 8 120 307C1421

120 240 39 30 120 8.7 250 307C1505

120 240 25 25 105 8.7 250 307C1501

150 300 12 20 90 8.7 110 307C1439

120 240 15 25 80 9.5 220 307C1465

125 250 20 20 105 9.5 220 307C1507

135 270 10 25 80 9.5 220 307C1469

150 300 10 20 105 9.5 220 307C1233

170 340 10 20 105 11.2 220 307C1234

110 220 23 20 80 14.5 300 307C1262

125 250 18 25 80 14.5 265 307C1254

Note 1 Note 2 Note 3

CUSTOM PTCR PELLET

DESIGN CAPABILITY

• Vishay Cera-Mite will customize

solid state overcurrent protector

PTCRs to your exact requirements

for telecommunication, power

supply, or general electronic

use. Providing great flexibility to

establish specific voltage, hold

current, time-trip characteristic, and

ambient temperature values.

• Each device must be evaluated

and ratings established per appli-

cation. Mechanical packaging

influences performance ratings.

Table 3

RATING CHART FOR CUSTOM PELLETS

DISC DIAMETER (2.5mm THICK) 6.5mm 8mm 9.5mm 11mm 12.5mm 14.5mm

Continuous Voltage Rating (rms)

(proportional to resistance) 100 – 300 100 – 300100 – 300 100 – 300 100 – 300 50 - 300

Resistance Range @ 25°C (ohms) 10 to 35 7 to 25 5 to 20 4 to 17 2 to 15 1 to 10

Continuous Carry Current (mA)

Ambient 25° to 50°C (inversely 60 – 120 75 – 175 100 – 200 110 – 250 130 – 400 150 – 600

proportional to resistance)

Approximate Minimum Power

to Trip or Reset (watts) 0.4 0.5 0.6 0.7 0.8 0.9

Interrupting Capability

A. Repetitive (25 to 300 VRMS)

Peak power in watts 600 700 800 900 1000 1100

B. Non-repetitive (for 10 ohm

pellet) I2t Let Through 2.5 4.0 7.5 15 20 30

Maximum Safe Interrupting

Voltage (rms) (voltage rating 300 350 400 450 500 600

is proportional to resistance)

Fig P-11

WIRE LEADED PTC

TELECOM THERMISTORS

Resettable current limiters featuring

hold current and voltage ratings for

telecommunication applications.

Fig P-12

TELECOM CURRENT LIMITERS

Rated Voltage = 60Vdc; Rated Current = 3A at rated voltage.

Note 1

Hold and trip

currents specified at

25°C ambient.

Note 2

R25 is nominal zero

power resistance

(± 25%) at 25°C.

Note 3

P/N suffix describes

options including:

Tape & Reel

Wire Size

Wire Style &

Length

Lead Spacing

Coating Material

32mm min

4.5mm

max

LS = 5mm

5mm

max

Tinned Copper Wire

22 AWG Standard

20 AWG on D=14.5mm

Pass-Thru Pulse

PTCR

1000

10 x 1000µ sec.

± 1000V peak

Rating applies to pellets with silver electrodes and pressure connections.

TRANSIENT VOLTAGE &

CURRENT

Because of the thermal storage

capacity of the ceramic PTCR,

transient surges do not cause tripping.

The PTCR is considered to be

transparent to these low energy

transients. Fig P-11 shows a typical

test circuit for such transients.

Table 4

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307C Overcurrent Thermistors

Vishay Cera-Mite

Document Number: 23089

Revision 14-May-02 ceramite.support@vishay.com

MAX. DESIGN LIMITS (APPROX.)

D (mm)

COATED VRMS I HOLD OHMS

17.5 600 40 mA 125

15 950 mA 0.8

19 600 45 mA 100

15 1.1 A 0.7

21 600 55 mA 80

15 1.2 A 0.6

22.5 600 60 mA 70

15 1.3 A 0.5

23.5 600 70 mA 60

15 1.4 A 0.45

25 600 80 mA 50

15 1.5 A 0.4

MAX. DESIGN LIMITS (APPROX.)

D (mm)

COATED V

RMS

HOLD

OHMS

5.5 600 5 mA 2000

15 150 mA 13

6.5 600 7 mA 1200

15 200 mA 8

8 600 10 mA 850

15 275 mA 6

9.5 600 13 mA 500

15 350 mA 4

11 600 20 mA 350

15 450 mA 2.5

12.5 600 22 mA 250

15 500 mA 2.0

14.5 600 30 mA 200

15 650 mA 1.5

16 600 35 mA 150

15 800 mA 1.2

PTCR Overcurrent Protection

VISHAY

RATED MAX. HOLD (IH) TRIP (IT) MAX. RES SWITCH D CERA-MITE

VOLTAGE VOLTAGE CURRENT CURRENT CURRENT R25 TEMP MAX. PART

VRMS VRMS mA mA A Ohms °C mm NUMBER

12 15 130 260 1.1 13 120 5.5 307C1455

12 15 170 340 2.4 6 105 8 307C1308

12 15 600 1200 10 1.2 105 16 307C1311

24 30 130 260 2.3 10 105 8 307C1315

24 30 175 350 3.4 6 105 9.5 307C1429

24 30 600 1200 11 1.3 105 17.5 307C1318

50 60 60 120 0.8 50 105 6.5 307C1321

50 60 120 240 2 12 105 8 307C1323

50 60 150 300 2.6 10 105 9.5 307C1548

50 60 325 650 10 3.5 105 14.5 307C1325

50 60 475 950 12 2 105 17.5 307C1326

120 140 60 120 0.6 50 105 6.5 307C1329

120 140 85 170 0.8 30 105 8 307C1330

120 140 95 190 1.5 39 105 11 307C1302

120 140 115 230 2 27 105 12.5 307C1303

120 140 105 210 1 20 105 9.5 307C1331

120 140 350 700 5 4.5 105 19 307C1333

240 375 20 40 0.2 600 105 6.5 307C1335

240 340 28 56 0.3 300 105 6.5 307C1336

240 310 31 62 0.33 240 105 6.5 307C1337

240 265 34 68 0.34 200 105 6.5 307C1338

240 265 40 80 0.45 125 105 6.5 307C1340

240 320 45 90 0.4 150 105 9.5 307C1339

240 320 55 110 0.5 100 105 11 307C1341

240 265 65 130 0.6 70 105 9.5 307C1342

240 265 90 180 1 45 105 11 307C1343

Note 1 Note 2 Note 3

Table 5

GENERAL PURPOSE PTC THERMISTORS OVERCURRENT PROTECTORS

GENERAL PURPOSE

PTC CURRENT LIMITERS

• Designed as resettable current

limiters, PTC thermistors offer an

alternative to conventional over-

current protection devices such as

fuses or circuit breakers.

• A wide variety of sizes and current

ranges are available for many

electronic, industrial and automotive

applications. Both standard parts and

custom designs are offered.

Fig P-13

4.5mm

max

5mm

max

Tinned Copper Clad Steel Wire

24 AWG when D < 9.5mm

22 AWG when D > 11mm to < 19mm

20 AWG when D > 21mm

CUSTOM CURRENT LIMITER GUIDELINES

Table 6

RANGE CHART FOR CUSTOM WIRE LEADED DESIGN

Conformal coating adds 1.5mm

APPLICATION CONSIDERATIONS:

•

• PTC current limiters are intended for service on

telecom systems, automobiles, or the secondary of

control transformers or in similar applications where

energy available is limited by source impedance. They are

not intended for application on AC line voltages where

source energy may be high and source impedance low.

•

• Fuses and circuit breakers result in total circuit

isolation after tripping. PTC thermistors provide a

current limiting function by switching to a high

resistance mode. Safety consideration must be given

to the potential shock hazard caused by the steady

state leakage current and voltage potential remaining in

the circuit.

•

• Wire leaded PTC current limiting thermistors are intended

for applications which expect a limited number of tripping

operations. Actual life is a function of operating parameters.

For high duty cycle applications, ceramic PTC pellets

mounted in spring contact mechanical housings are

preferred.

•

• Wire size, wire type and coating material can be used to

precisely tailor required operating characteristics.

•

• Options Include: Tape & Reel; Wire Forms; Lead

Spacings.

Resistance is proportional

to voltage and inversely

proportional to hold

current (IH)

CL - Cut Leads are Standard 4.75± 0.5mm

LS - Standard Lead Spacings:

5mm when D ≤11mm

7.5mm when D = 12.5 to 17.5mm

10mm when D ≥19mm