Circuit Protection with Non-Linear Resistors
r esistive p r oducts
V I S H AY I N T E R T E C H N O L O G Y, I N C .
P TC a nd NTC T he r mi sto r s,
T hrough - Hole Va r isto r s, SMD T hin - Film Chip Fu se s
capabilities
w w w. v i s h a y. c o m
Circuit Protection with Non-Linear Resistors
Using PTC – Positive Temperature Coefficient Thermistors
The electrical resistance of PTC (positive temperature coefficient) thermistors increases and decreases as the ambient
temperature increases and decreases. PTC thermistors are used for voltage and/or current overload protection, temperature
protection, inrush current generation, and as a heating element. They protect a wide range of circuits, including line cards,
set-top boxes, and private automated branch exchanges in telecom applications; airbag and temperature control devices in
automobiles; power supplies and battery chargers in electronic data processing applications; and in other consumer products.
PTC Protection Principles
Features
Part numbers
• Different voltages in function of the application:
20 V, 30-60 V, 145 V, 265 V
Overvoltage/overcurrent:
• Several executions: naked, leaded, taped,
SMD leadframe
• 30-60 V series:2381 66x 5xxx1 (UL approved)
• Wide range of trip and hold currents: from
17 mA up to 4.5 A trip currents
• 265 V series: 2381 66x 5xxx3 (UL approved)
• 20 V series:
2381 66x 5xxx4
• 145 V series: 2381 66x 5xxx2 (UL approved)
Overtemperature:
• Small ratio between trip and hold currents
(It/Ih = 1.5 at 25 °C)
• Tn: 70 ºC to 170 ºC: 2381 671 91xxx
Log R
• Wide range of resistance: from 0.16 Ω up to 3 kΩ
• High maximum inrush current: up to 33 A
• UL approved series
PTC
Vsupply
Normal
Operating
Zone
Load
2Rmin
Rmin
Protecting
Zone
Figure 1
100
Ts
T
Log I
time (s)
Itrip
10
Ihold
1
0.1
0
2000
4000
6000
8000
10000
I (mA)
Figure 2
Vmax
Log V
When connected in series with the input of an electrical or electronic circuit (see Figure 1), such as a small motor or power
supply, the PTC thermistor acts as a self-resettable fuse, protecting the circuit against current, voltage and temperature
overload conditions.
In normal operating conditions the PTC resistance is low (see Figure 2), and the current is below its hold value (Ihold). However,
an overload will quickly heat up the PTC thermistor until, at around switchtemperature (Ts), its resistance becomes high, limiting
the current to far below its trip value (Itrip), and so protecting the circuit.
Using NTC – Negative Temperature Coefficient Thermistors
The electrical resistance of NTC (negative temperature coefficient) thermistors increases as the ambient temperature
decreases, and decreases when temperature increases. NTC thermistors are used for overtemperature protection in PCs,
power supplies, and motherboards; Li-ion battery protection in fast chargers; and in digital scan cameras, fire and smoke
detectors, TCXOs, and other automotive, consumer, and industrial applications. They are generally included in dividing
or Wheatstone bridges and can provide a measuring voltage to analog-digital converters. They also allow to control the
temperature compensation of displays and regulation of temperature with opamps or more complex IC’s.
Features for Circuit Protection:
• Several executions: leaded and SMD in cases from 0402 to 1206
• Large resistance range: from 3.3 Ω to 470 kΩ
• Temperature range: – 40 °C to + 155 °C
• SMD Termination: Ni and pure Sn
• Customized types available upon request
Example of NTC Circuit Protection in PC Cooling Fan
Sensor (pos. a)
Processor
Socket
Temperature
R=1 S=Q=0
THigh
RNTC
+
–
+
Rlow
Sensor (pos. c)
Sensor (pos. b)
VC
Rhigh
Heatsink
A
A
+
C
–
A
+
C
–
+
–
+
–
Fan
Motor
R=S=0
Q=0 (unch.)
TLow
R=0 S=Q=1
–
Time
Q
Q=0
Vcc
S
R Q
Q
0
R=S=0
Q=1 (unch.)
Q=1
Q=1
Fan Off
On
Off
Time
Using Through-Hole Varistors
VDRs (voltage dependent resistors), or varistors, are used for transient surge suppression. Surge suppression circuits are
commonly used in computers, automobiles, telecom and industrial equipment, domestic appliances, and other consumer
products.
Specifications Table
Standard Series: 2381 592/593/594/595/596
Vrms from 14 V to 680 V
Vdc from 18 V to 895 V
Sizes from 5 mm to 20 mm
Can absorb surges up to 6,500 A
High-Surge Series: 2381 582/583/584/585/586
Vrms from 11 V to 680 V
Vdc from 14 V to 895 V
Sizes from 5 mm to 20 mm
Can absorb surges up to 10,000 A
Example of VDR Circuit Protection in PC
Dangerous Voltage
(without VDR)
VAB
Line Inductance
Clamping
Voltage
Safe Voltage
(with VDR)
Mains
220 V
Mains
Line Capacitance
I
VDR
VAB
Fuse
Time
1.5 A
Short
Circuit
Fuse
Opens
M
Short
Circuit
Washing Machine Motor
220 W
HOME
COMPUTER
Circuit Protection with Non-Linear Resistors
Using SMD Thin Film Flat Chip Fuse
SMD thin film flat chip fuses feature very quick-acting fuse characteristics with outstanding stability, thanks to a highly
controlled manufacturing process and Vishay’s advanced thin film technology. Available in standard metric case sizes, they are
designed to provide secondary overcurrent protection for power inverters, motion-control units, dc-to-dc converters, battery
chargers, and low-voltage power supplies in information technology, telecommunications, automotive, medical, and audio/
video systems.
Features
Characteristics of SMD Thin Film Chip Fuses
• Available in 0603, 0805, and 1206 cases
• Standard alumina substrate
• Low ohmic metal film alloy fuse element
10
MFU Chip Fuse Series
• Structuring by Photolithography
1
• Low ohmic Cu/Ni/pure Sn terminations
• Epoxy lacquer
0.1
t[s]
• Fuse current adjustment by precise contour variation
of the fuse element geometry (l/b/h)
Benefits
0.01
pre-arcing time min.
pre-arcing time max.
1E-3
• Fast – very quick-acting (FF)
• High-precision blow characteristics
1 E-4
• High reliability
• Stability verified in accordance with IEC 60127-4
and UL 248-14
1 E-5
0
1.25
2
4
6
8
10
12
IR/I
• First chip fuse series in standard SMD sizes approved
by UL and VDE
MFU Current Range Table
Rated Current (A) 1)
Size
Fuse
Characteristics
0.5
1
1.6
2.0
0402 2)
FF
X
X
X
X
0603
FF
X
X
X
0805
FF
X
X
X
1206
FF
X
X
X
3.15
4.0
X
X
X
X
X
X
X
X
X
5.0
X
1) Other values of rated current are available. Please refer to the MFU Chip Fuse datasheet.
2) MFU 0402 available on request.
NOTICE Specifications of the products displayed herein are subject to change without notice. Vishay Intertechnology, Inc., or anyone on its behalf, assumes no responsibility or liability for any errors or inaccuracies. Information
contained herein is intended to provide a product description only. No license, express or implied, by estoppel or otherwise, to any intellectual property rights is granted by this document. Except as provided in Vishay’s terms and
conditions of sale for such products, Vishay assumes no liability whatsoever, and disclaims any express or implied warranty, relating to sale and/or use of Vishay products including liability or warranties relating to fitness for a particular
purpose, merchantability, or infringement of any patent, copyright, or other intellectual property right. The products shown herein are not designed for use in medical, life-saving, or life-sustaining applications. Customers using or
selling these products for use in such applications do so at their own risk and agree to fully indemnify Vishay for any damages resulting from such improper use or sale.
Semiconductors:
Rectifiers • Small-Signal Diodes • Zener and Suppressor Diodes • MOSFETs
• RF Transistors • Optoelectronics • ICs
Passive Components:
Resistive Products • Magnetics • Capacitors • Strain Gage Transducers and
Stress Analysis Systems
One of the World’s Largest
Manufacturers
Worldwide Sales Contacts
of Discrete Semiconductors and Passive Components
The Americas
EUROPE
united states
germany
Vishay Americas
One Greenwich Place
Shelton, CT 06484
United States
Ph: +1-402-563-6866
Fax: +1-402-563-6296
Vishay europe sales GmbH
Geheimrat-Rosenthal-Str. 100
95100 Selb
Germany
Ph: +49-9287-71-0
Fax: +49-9287-70435
Asia
france
singapore
Vishay S.A.
199, blvd de la madelEine
06003 nice, cedex 1
France
Ph: +33-4-9337-2920
Fax: +33-4-9337-2997
Vishay intertechnology
Asia Pte Ltd.
25 Tampines Street 92
Keppel Building #02-00
Singapore 528877
Ph: +65-6788-6668
Fax: +65-6788-0988
p.r.C.
Vishay Trading (Shanghai) Co., Ltd.
(Shanghai Representative Office)
Room D, 15F, Sun Tong Infoport plaza
55 huai hai west road
200030 shanghai
P.R.C.
Ph: +86-21-5258-5000
fax: +86-21-5258-7979
netherlands
Vishay bccomponents b.v.
hurkestraat 31
p.o. box 8766
5652 ah eindhoven
netherlands
Ph: +31-40-2590-700
Fax: +31-40-2590-777
japan
vishay japan CO., LTD.
Shibuya 3-chome Square Building 3F
3-5-16 Shibuya
Shibuya-Ku
Tokyo 150-0002
Japan
Ph: +81-3-5464-6411
fax: +81-3-5464-6433
w w w. v i s h a y. c o m
VSA-PL0035-0602