Auto Cooling Fan Circuit With IC LM741

This circuit is auto fan or cooling fan for your computer,electronic project,the circuit is simply to apply to your project .

Couple Notes:

Th1, the 50K thermistor is a standard type. I was looking for a bar or rectangular thingy. Available from Tandy / Radio Shack. Almost any type will do. I experimented with different models of 22K to 100K and everything worked fine after replacing the trimmer pot and a little “tuning.

The one used in the diagram above circuit has been a model of 50K by Fenwal (# 197-503LAG-A01). The 50K was measured exactly at 25 ° C and a tolerance of 10%. The increase in resistance as temperatures fall. Tolerance for my application (cooling a PowerSupply coolrib wide) is 10%.

Another name for this thing is “NTC”. NTC stands for “negative temperature coefficient” which means that when the temperature decreases the resistance of the thermistor will increase. You may need to shop for the lowest price. Some are thermistor may have a minimum of $ 4.00, but for $ 55.00 Canadian dollars for the type of glass encapsulated (best).

I replaced my 60K thermistor for a type of glass hermetically sealed such as the environment so that my application may contain corrosive particles that can affect performance at a future date.

Bourns trimmer P1 is an ordinary rule and a wide temperature range of this circuit. I used the 10-ballot style for a little fine tuning, but the kind of regular job application.

R1 is a “security” of resistance where the pot P1 trimmer is adjusted all the way to ‘0 ‘ohm. Just then the thermistor would receive the full 12 volts and so hot that puts blisters on your fingers …
R3 feeds back a little in the hysteresis op-amp to eliminate the chattering relay, when the temperature of the thermistor reaches its threshold. Depending on the application and the type used in Q1 and Re1, start with about 330K and reduce its value until satisfied. The value of 150K reported in the scheme worked for me. Reducing the value of hysteresis R2 more resources, just do not use more than necessary. Or temporarily use a trimmer pot and read the value. 120K worked for me.

Transistor Q1 may be a 2N2222 (A) 2N3904, NTE123A, ECG123A, etc. not critical at all. It only acts as a switch for the relay in almost any type will work, until he could provide the current necessary to activate the relay coil.

D1, 1N4148, acts as a spark arrestor when the relay contacts open and eliminates false triggering. For my application, the 1N4148 was good for the relay I used only 1 Amps small. However, you can use a variety of diodes here, my next choice would be a regular target 1N4001 or something and should be used if the type of relay that can handle more than 1 ampere.

Digagram circuit, PCB and layout are up to date with C1, C2, R7 and LED. C1 and C2 are new to eliminate the switching noise of the relay in some applications. The optional LED, and resistance were added to the circuit and layot for your convenience. The relay used in this and the kit is a type 12V/0.5A small. If the relay rattles increase the feedback resistor R3 to 180K or a little “higher, and small ceramic cap on the coil connections in parallel with the diode D1. Diode 1N4148 is specified for a small relay. If you use a relays used as a 1N4001 or 1N4004.

If you like to make your own PCBs, try the following. The PCB is equipped with holes for the relay, but may not take your particular relay. It was designed for a type Aromat HB1 DC12V. The variety and model of the relay is only for adults. How to mount then? Well, I left a lot of space on the PCB to mount your relay. You can also mount below, and connect the cables individually. The use of silicone adhesive, cyanoacrylate ester (crazy glue) or double-sided tape to hold the relay in place. Works well. Note that the PAC and the setting Page Not according to the circuit diagram regarding the coupling of fans. The PCB is about 1.5 x 3 inches (4.8 x 7.6 mm)
If you print a PCB inkjet printer is probably not to scale. Try to mount an 8-pin IC socket on a printed copy to ensure it matches the scale before printing on a sheet of transparency and make the PCB …

Auto Fan PCB Picture

Part , Description , Radio Shack , Digi Key , Newark Notes
IC1 LM741 Op-Amp 276-007 LM741CN-ND LM741CN NE741,µA741, etc.
Q1 2N2222A transistor 276-2009 2N2222A-ND 2N3904 See text
D1 1N4148 Diode 276-1122 1N4148GICT-ND 1N4001 1N4001, or others
Th1 50K Thermistor KC005T-ND 96F3309 KC005T in prototype
Re1 12V Relay 275-249 Z753-ND 83F8057 RS is 1A
R1 15K, 5% resistor 84N2487 brown-green-orange
R2,R5 10K, 5% resistor 84N2479 brown-black-orange
R3 150K, 5% resistor 84N2485 brown-green-yellow
R4 4K7, 5% resistor 271-1330 50N1628 yellow-purple-red
R6 1K, 5% resistor 271-1321 50N6012 brown-black-red
R7 1K8, 5% resistor brown-gray-red
P1 100K Trimmer Pot Bourns
C1 10uF/25V Capacitor Electrolytic
C2 0.01uF, Capacitor Ceramic
Led Red, 3mm Light Emitting Diode

Auto Fan Part on Board

Spare parts:

Q1 = 2N3053, 2N3904, NTE123A, ECG123A, NTE128, ECG128, etc.
D1 = 1N4001, NTE519, ECG519, NTE116 etc.
Th1 = Thermistor, 22K – 100K. 50K used in the prototype.
Re1 = Relay, Type 842-1C-C “Fashion Electronics. Order # 50-333-0 (1.55 $)
Reed relay works well.

Thank for good circuit :

http://www.uoguelph.ca/~antoon/circ/auto-fan.html