Presented By
Prashant Tripathi

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1. Introduction
B.K.Birla Institute of Engineering and Technology is a newly established institution in the field of Engineering and Technology. Since last few years ago it is representing itself as a leading institute in Rajasthan.
The minor project is one of the most important courses offered by the Rajasthan Technical University for the final year student in Engineering Field. It gives a way to work and apply the practical knowledge in an appropriate way.
1.1 Aim of the project
The focused aim of the project is to control a 12V DC fan using a power electronic circuit works on the operation of Thermistor. A rectified 12V DC input is given to the circuit which contains an arrangement of Thermistor, Relay, Potentiometer and various other electronic components like Diode, Transistor and Resistors.
1.2 Circuit Diagram
Fig:01- main circuit
2.Component Selection
2.1 criterion
In this we have a particular criteria for the selsction of of various components as
1.Transformer:-230V /12V
2.Potentiometer:-1k to 10k
3.Op-Amp:- +12V / 0 V
4.Relay:- 12 V to 20V
5.Thermistor :- 1KΩ to 100KΩ depending upon the value of resistors
2.2 final selected components
The various electronic components used in this project are tabulated below
S.No. Components Specification
1. Resistors 270Ω,470 Ω,10K Ω ,10K Ω,150K Ω, 4k7 K Ω,
1.8K Ω, 1K Ω
2. Capacitor 3*(1000µf ,0.7 threshold Voltage )
3. Ceramic C 1000µf ,0.7 threshold Voltage
4. Fan 12V DC
5. Transformer 220/12 zero 12 (Center tapped)
6. Diode p-n junction diode
7. Transistor npn type
8. Regulator 7812 for regulated supply
9. Op-Amp IC 741 , 12 V + and 0 ground
10. Variable resistor 1K Ω
11. Relay 12V DC
12. LED Passive Red, optoelectronic Green
13. Thermistor ntc type,1K Ω
3.Simulation
The simulation of the circuit is done in the psim software. The simulation circuit diagrame is shown below
Fig 03:- Output waveforms from simulation circuit (When R=400Ω)
4. Transformer Design
For the construction of the transformer we have the following calculations are made:-
Primary Voltage=230V
Secondary Voltage=12V
Secondary Current=500mA
Core area=1.152*√ (output voltage*output current) square cm
Now, we have
Turns per volt=1/ (4.44*0.0001*frequency*core area*flux density)
The current in primary winding is given by
Primary current=sum of(output volts* output amps)/(primary volt*efficiency)
The number of turns in primary winding is given by
Primary turns=Turns per volt*Primary volts
Primary Winding area= primary turns/Turns per sq. cm.
Secondary turns=1.03(turns per volt*secondary volts)
The window area for secondary winding is
Secondary window area =secondary turns/turns per square cm.
Core area:
Total window area=Primary Window area+ Sum of Secondary Window areas+ space for former and insulation
Gross core area=core area/0.9 sq. cm
Tongue width=√Gross core area cm
Stack height=Gross core Area/Actual Tounge Width cm.