A posistor is a radio component-a semiconductor with a positive temperature coefficient of resistance.The basic principle of operation of this part is simple:when heated, the posistor increases its resistance or when current flows through the posistor, it heats up and increases its resistance.The higher the resistance, the lower the current passing through the circuit.Main application: as a gradual current limiter and heating element.
You can find such a detail on the board of old televisions and monitors and it serves there to supply a short-term current to the demagnetization coil of the kinescope.The part is made in a black case with two or three terminals and inside there are one or two posistors in the form of round “tablets”.
It is used to start electric motors, you can see it on the relay in the refrigerator; as a heating element, you will see a posistor in glue guns; I have already written about demagnetization of kinescopes.Here is the actual diagram from the TV, which shows the connection of the posistor to the coils L1 and L2.
The main characteristics are the resistance of the part at normal temperature; operating voltage; attenuation characteristics and residual current.
You can check the part with an ohmmeter.At room temperature, my posistor shows a resistance of 19.5 ohms.When heated, the resistance begins to increase rapidly.
I connected this posistor from the TV in series to a 40W incandescent lamp.At a power supply voltage of 220 Volts, the lamp lights up at first, but after 15 seconds it goes out.The posistor at this time will be heated by the passing current, and the lamp will not shine until the circuit is de-energized and the posistor cools down.
Glue guns use this principle of heating a posistor to melt pencils.
