## Temperature Controlled DC Fan using Thermistor (Mini Project)

Hello friends, in this post we are going to make one simple mini project which is temperature controlled DC fan using a thermistor. In this mini project, we are going to control the speed of the DC fan automatically as the surrounding temperature changes. Thus when the temperature of surrounding increases speed of fan also increases and when temperature decrease speed of fan also decreases. This is achieved by using the principle of the thermistor.

## Components required

• R1 = 4.7K
• R2 = 47 Ohm
• NTC Thermistor = 4.7K

• Potentiometer (Vr) = 500K
• OP AMP IC 741
• Transistor T1 = BD140 (or other PNP transistor may work)
• 12V DC fan which is also used in computer (CPU)
• Diode 1N4007
• 12 V DC power supply

## Circuit diagram

The following figure shows a circuit diagram of temperature controlled DC fan using a thermistor.

## Working

The basic working principle of temperature controlled DC fan is based on the working principle of the thermistor. The thermistor is a component which changes its resistance as its temperature changes. There are two types of thermistor available which are NTC i.e. negative temperature coefficient and other is PTC which is positive temperature coefficient.

In temperature controlled DC fan, we have used an NTC type thermistor. It is called NTC because its resistance increases when its temperature decreases and vice verse. Similarly, in PTC, its resistance increases when temperature increases and vice verse.

Op amp IC741 is used as a voltage comparator which compares the voltage between its two inputs i.e. inverting and non-inverting terminals. Pin number 2 is inverting terminal which is connected to the potentiometer and pin number 3 is a non inverting terminal which is connected in between thermistor and R1 which makes a voltage divider circuit. Thus the output of op amp is responsible for the speed of the fan.

When the temperature of surrounding increases, the temperature of thermistor also increases which causes its resistance to decrease, therefore voltage divider circuit causes more voltage across pin number 3. Thus the output voltage increases causing the speed of the fan to increase.

## Audio Amplifier using Op-Amp: Electronics Project

This article provides an information about how to make an audio amplifier using an opamp. We will also try to explain the working of this audio amplifier using an opamp. We have already studied some important applications of the operational amplifier such as op-amp comparator, op-amp integrator in the previous articles. Today we are going to learn another important application of op-amp as an audio amplifier and its working.

We know that the output of most of the communication receivers is the audio amplifier. Important characteristics of the ideal audio amplifier are listed below.

1. High gain.
2. Distortion should be minimum in the audio frequency range. (20Hz to 20KHz)
3. Input resistance or impedance should be very high.
4. Low output resistance to provide optimum coupling to the speaker.

If we use the operational amplifier in the audio amplifier, then it will cover all the characteristics listed above so as to make an ideal audio amplifier.

## Circuit diagram

The following figure shows the circuit diagram of the audio amplifier using operation amplifier.