Heat Sensor Circuit Using Transistor

Circuit diagram of fire alarm using germanium diode.

Heat sensor circuit using transistor. It turns on a buzzer whenever the temperature exceeds the limits and vice versa. This simple circuit is easy to construct and test. The temperature detection is carried out by a transistor mounted on the heat sink and or close to the power transistor in question. Operating principle of heat sensor circuit diagram.

This circuit utilize ntc negative temperature coefficient thermistor hence the resistance value of this device decrease when the temperature rises. The clear explanation about these components is as follows. Diode 1n4148 and variable resister of 1k ohm are used here to set a reference or threshold level for the sensitivity of heat. Simple heat sensor circuit designed to give alert sound when the temperature reaches the desired threshold here we can adjust the temperature threshold level using variable resistor rv1.

This temperature property of transistor is used here to use it as a heat sensor. Here transistor bc547 is used as a heat sensor. The base of a transistor gets bias with the ntc thermistor along with the variable resistor whereas the buzzer is connected to the output of the transistor. As both these active parts have identical properties as far as ambient temperature changes are concerned they both complement each other.

A bc548 transistor a thermistor 110 ohms are a few components used in a heat sensor. And the sensitivity of the circuit can be adjusted by rotating the knob. The dr25 is made reverse biased in the circuit. In the circuit diagram the temperature detector is transistor t1 and its base emitter voltage is compared to the reference level at the junction of d1 and r1 via the preset p1.

Simple heat sensor circuit designed to give alert sound when the temperature reaches the desired threshold here we can adjust the temperature threshold level using variable resistor rv1. A bc548 transistor a thermistor 110 ohms are a few components used in a heat sensor. The simple heat sensor circuit is as shown below. As the temperature of pn junction increase transistor starts conducting to some extent.

It will conduct only when it is more than 70degree of room temperature. Using a transistor bjt as the temperature sensor in the present design a diode and a transistor are configured in the form of a bridge network. The common emitter phototransistor circuit configuration is possibly the most widely used like its more conventional straight transistor circuit. The dr25 germanium diode is heat sensor which will conduct when temperature is increased at certain point.

Using diode for creating a reference voltage. Heat sensor circuit senses the heat from various electronic devices like amplifiers computer etc and thus generates the warning alarm. The clear explanation about these components is as follows.