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PTC Thermistors: Definition & Function
Thermistors are temperature dependent resistors and "PTC"
stands for Positive Temperature Coefficient of resistance.
Ceramic PTC thermistor exhibits a highly positive temperature
coefficient (Figure 1) where its resistance increases rapidly past
a reference temperature (or Curie temperature).

The PTC thermistors we produce are based on doped semi-
conductive BaTiO3 ceramics.

FIGURE 1:PTC and NTC thermistor resistance-temperature (R/T) profiles

In general, applications using PTC thermistor can be categorized according to three unique behaviors: resistance-temperature (R/T), current-voltage (I/V), and current-time (I-t) behaviors. Table 1 gives generalized plots describing these behaviors and their related applications. In many cases, all three behaviors are considered during the design phase.

Typical Plots
Temp controls
Over-temp protections
Over-current protections
Self-regulating heating
Motor starting
Time delay

Key points to consider when using PTC thermistors :
PTC performance is a function of heat dissipation conditions, thermistor dimension, Curie temperature,
thermistor resistance, applied voltage, etc.
PTC thermistor auto-regulates its electrical power in response to thermal dissipations (e.g. a general cooling
will "prompt" thermistors to consume more electrical power to maintain its preset temperature).

Advantages of PTC thermistor :
Insensitivity to voltage fluctuations.
Broad operating voltage range (3V to 230V).
No controls for temperature or power needed.
Self-setting after recovery from faults.
Extended electrical & thermal stability Does not glow when energized (no oxygen consumption).
Poses no fire hazards.
Suitable for wide range of applications.

VR =Rated voltage
VD =Breakdown voltage
VW/S =Withstanding voltage
VMAX =Maximum voltage
IR =Rated (non-action) current (below this current the PTC thermistor remains in low-resistance state)
IS =Switching (action/trip) current (above this current the PTC goes into high-resistance state)
IRES =Residual current (corresponding current at steady state applied operating voltage)
IMAX =Maximum current
IP-P =Peak to peak current value
R25C =Resistance (measured @ 25�J ambient)
RMIN =Minimum resistance
�\ =Temperature coefficient on a R/T curve
�_ =Dissipation factor (mW/�J)
TSURF =Thermistor surface temperature
TOP =Operating temperature
PW =Power consumption (electrical wattage measured at a particular)
PR =Rated power
PG =Gauge power
TSW =Switching temperature (temperature corresponding to the resistance which is 2 �� RMIN)
Tr =Reference temperature
�nOP =Operating time (time period before thermistor switch from low to high resistance state)
�nR =Recovery time (total time required for thermistor to return to its non-action state)
�nH =Thermal reaction time
�X =Thermistor disk diameter
�XO =Thermistor outer ring diameter
�XI =Thermistor inner ring diameter
DTR =Detective Temperature range

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