Taiwanese-Sunlead Electrical Corp.-PTC, PTCR, heater, heating elements, motor starters, ceramic PTC thermistors as protectors-controllers-sensors, temperature sensors, transformers. Commerce Manufacturer Machinery Taipei China Asian Pacific R.O.C.

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

Function

Applications

R/T

��	Sensors
��	Temp controls
��	Over-temp protections
��	Over-current protections
��	Self-regulating heating
��	Degaussing
��	Motor starting
��	Time delay

I/V

I/t

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.

ABBREVIATED LETTER CODES

V_R	=Rated voltage
V_D	=Breakdown voltage
V_W/S	=Withstanding voltage
V_MAX	=Maximum voltage
I_R	=Rated (non-action) current (below this current the PTC thermistor remains in low-resistance state)
I_S	=Switching (action/trip) current (above this current the PTC goes into high-resistance state)
I_RES	=Residual current (corresponding current at steady state applied operating voltage)
I_MAX	=Maximum current
I_P-P	=Peak to peak current value
R_25C	=Resistance (measured @ 25�J ambient)
R_MIN	=Minimum resistance
�\	=Temperature coefficient on a R/T curve
�_	=Dissipation factor (mW/�J)
T_SURF	=Thermistor surface temperature
T_OP	=Operating temperature
P_W	=Power consumption (electrical wattage measured at a particular)
P_R	=Rated power
P_G	=Gauge power
T_SW	=Switching temperature (temperature corresponding to the resistance which is 2 �� RMIN)
T_r	=Reference temperature
�n_OP	=Operating time (time period before thermistor switch from low to high resistance state)
�n_R	=Recovery time (total time required for thermistor to return to its non-action state)
�n_H	=Thermal reaction time
�X	=Thermistor disk diameter
�X_O	=Thermistor outer ring diameter
�X_I	=Thermistor inner ring diameter
D_TR	=Detective Temperature range