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| 型号： | 232267191105 |
| 厂商： | Vishay Intertechnology,Inc. |
| 元件分类： | 热敏电阻 |
| 英文描述： | PTC Thermistors, For Temperature Protection |
| 中文描述： | PTC热敏电阻，温度保护 |
| 文件页数： | 3/5页 |
| 文件大小： | 75K |
| 代理商： | 232267191105 |
2322 671 91...
Vishay BCcomponents
PTC Thermistors, For Temperature Protection
www.vishay.com
174
For technical questions contact: nlr.europe@vishay.com
Document Number: 29074
Revision: 10-Oct-03
APPLICATION SPECIFIC DATA
Negative Temperature Coefficient (NTC) thermistors are well known for temperature sensing. What is not well known, however,
is that Positive Temperature Coefficient (PTC) thermistors can be used for thermal protection. Although their operating principles
are similar, the applications are very different; whereas NTC thermistors sense and measure temperature over a defined range,
PTC thermistors switch at one particular temperature.
Just like thermostats they protect such equipment and components as motors, transformers, power transistors and thyristors
against overtemperature. A PTC thermistor is less expensive than a thermostat, and its switch temperature can be more
accurately specified. It is also smaller and easier to design-in to electronic circuitry.
So how does it work The PTC thermistor is mounted in thermal contact with the equipment to be protected, and connected into
the bridge arm of a comparator circuit, such as shown in Fig.1. At normal temperature, the PTC thermistor resistance (R
than R
s
(see Fig.2), so the comparator's output voltage V
O
will be low. If an equipment overtemperature occurs, the PTC
thermistor will quickly heat up to its trigger or nominal reference temperature T
much higher than R
s
, causing V
O
to switch to a high level sufficient to activate an alarm, relay or power shutdown circuit.
p
) is lower
n
, whereupon its resistance will increase to a value
APPLICATION EXAMPLES
As soon as one or more of the windings becomes too hot, the
motor is switched off.
MBD129
θ
θ
θ
Fig.3 Temperature protection of electric motors
MBD126
θ
θ
θ
θ
A
The PTC thermistors located above the fluid level will be
heated to a temperature greater than T
When immersed they are cooled such that their
resistance value is reduced.
n
.
Fig.4 Liquid-level indication.
MBA921 - 2
trigger
temperature
Tn
Rp
(R1 = R2)
Rs
Rp
(R1 = R2)
Rs
Vo
T ( C)
Fig.2 Typical switch characteristic.
MBA920
PTC
thermistor
Rp
R
f
L
R
Rs
R1
R2
VO
θ
Fig.1 .Typical comparator circuit.
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相关代理商/技术参数 |
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|---|---|
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