PTCSL20T111DBE

Document Number: 29012 For technical questions, contact: nlr@vishay.com
www.vishay.com
Revision: 08-Jun-09 63
2381 671 911../PTCSL..T....BE
PTC Thermistors, Mini Radial Leaded
for Over-Temperature Protection
Vishay BCcomponents
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
p
) is
lower 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
n
, whereupon its resistance will increase to a value
much higher than R
s
, causing V
O
to switch to a high level sufficient to activate an alarm, relay or power shutdown circuit.
APPLICATION EXAMPLES
As soon as one or more of the windings becomes too hot, the
motor is switched off.
+ θ
+ θ
+ θ
Trigger
temperature
T
n
V
O
T (°C)
R
p
> R
s
(R1
= R2)
R
p
< R
s
(R1
= R2)
PTC
thermistor
R
p
R
L
R
f
R
s
R1
R2
+ θ
V
O
Fig. 2 Typical switch characteristic
Fig. 1 Typical comparator circuit
Fig. 3 Temperature protection of electric motors
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Revision: 02-Oct-12
1
Document Number: 91000
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PTCSL20T111DBE

Mfr. #:
Manufacturer:
Vishay
Description:
Thermistors - PTC 110/C PTC THERMISTOR YELLOW
Lifecycle:
New from this manufacturer.
Delivery:
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