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A Posistor is actually Murata's "name brand" for a device called a Positive Coefficient Thermistor. Used in many in-rush current control circuits, a positive coefficient thermistor is a resistor that starts with a relatively low resistance value at room temperature (25C) then, when heated from current flowing through it, its value quickly rises to a very high resistance.
One very common use of this device is to control the current flow through a CRT degaussing coil on picture-tube style (CRT) televisions and monitors.
These devices come in either positive coefficient thermal values (PTC) (eg: resistance increases as temperature / current increases) or negative coefficient values (NTC) (eg: resistance decreases as temperature / current increases).
Manufacturers include Nichicon, Murata, Vishay and a myriad of discrete device companies.
(Eric Peterson, Dunedin FL)
