Thermistor Controlled Transistor Switch Demonstration

This is a demonstration of a transistor switch controlled by a thermistor. This circuit uses a thermistor or a thermally controlled variable resistor. The value of the thermistor decreases with increase in temperature in an NTC thermistor. When the thermistor is heated using a flame or heat from any other source, the resistance of the thermistor decreases. The decreased resistance of the thermistor will raise the potential difference at the base. More current flow through the resistor and to the base of the transistor. The base voltage increases above 0.7 volts and the transistor begins to conduct. The current flows through the emitter and collector of the transistor. The flow of current through the transistor cause the led that is connected in series with the collector of the transistor and the current limiting resistor to glow.

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