How To Make A Temperature Controlled DC Fan Using An NTC Thermistor

What is a Temperature Controlled DC Fan?

Dynamic control of DC appliances by the application of varying heat levels is common nowadays. A Prime example would be a temperature controlled fire extinguishing systems that senses the thermals of any burning flame or heat source around it and triggers a water sprinkling system to go off when the heat from the flame goes above a certain threshold. Also, a wide variety of operational procedures used in process control industry are streamlined by the application of temprature control and monitoring. So, in today’s tutorial we are going to go over a step by step procedure on how To Make A Temperature Controlled DC Fan Using An NTC Thermistor.

The heart of this circuit is an NTC (Negative Temprature Co-efficient) thermistor. An NTC thermistor is a type of resistor whose resistance decreases with the increase in temperature. They are made out of a combination of metal oxides which are passed through the sintering process which gives negative electrical resistance versus temperature (R/T) relationship to it. By having a large -ve (R/T) slope, a small change in temperature results in a huge change in the electrical resistance of the thermistor.

Hardware Component

You will need the following parts to build this project:

S.No	Component	Value	Qty
1)	Thermistor	NTC, 10K	1
2)	Voltage Regulator	LM7806	1
3)	DC Fan	6V	1
4)	Potentiometer	50K	1
5)	Capacitor	0.1uF	1
6)	Soldering Iron	45W – 65W	1
7)	Soldering Wire With Flux	–	1
8)	Veroboard	–	1
9)	DC Battery	9V	1
10)	Battery Clip	–	1
11)	Jumper Wires	–	As per need

NTC Thermistor

BD139 Pinout

Useful Steps

1) Solder the BD139 transistor on the veroboard.

2) After that, solder one fixed end of the 50K pot with the base terminal of the transistor. Then, solder the variable end & the fixed end of the pot with the GND of the circuit.

3) After that create a voltage divider circuit by connecting one end of the 10K NTC thermistor with the base of BD139 transistor & the other end with the Vcc of the circuit.

4) Now solder one terminal of the Brushless DC fan with the 10K thermistor & other with the collector terminal of the BD139 transistor.

5) Power the circuit using a 6V voltage regulator (LM7806).

6) Test the circuit by bringing it near to a heat source.

Circuit Diagram For Temperature Controlled DC Fan

Working Explanation

The working of this circuit is actually pretty simple. On powering up the circuit & bringing it close to a heat source the resistance of the NTC thermistor begins to decline. Here the 10K NTC thermistor & the 50K pot operate as a voltage divider circuit, where the preset pot sets the switching level for the temperature on which the transistor should switch.

When the resistance of the NTC thermistor falls below a certain threshold, such that the signal at the base of the BD139 transistor is well within the switching voltage. The transistor switches ON and the DC Fan connected to the collector output also turn ON. As the temperature around the 10K thermistor reduces, it’s resistance increases, which subsequently diminishes the control signal at the base of the BD139 transistor and the DC fan switches OFF.