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Cooling Fan Controller Using Temperature Sensor LM35
The project presented here is a low-cost solution for heat management of the heatsink and various equipment that requires automatic control of a cooling Fan. The project is built using a very cheap LM358 OPAMP. LM358 is used as a comparator, and a trimmer PR1 is provided to set the temperature threshold (Fan ON trigger point). LM35 is used as a temperature sensor, it outputs an analog output voltage that is proportional to temperature. Capacitors C2 and C3 are bypass capacitors, D2 is a clamp diode to protect the Q1 MOSFET from reverse electromagnetic noise coming from the fan. Capacitor C1 helps in noise control while Fan is ON/OFF. LED D1 indicates Fan ON/OFF operations. Q1 MOSFET DMG3418L-7 can handle current up to 4A. LM35 can be mounted directly on the heatsink using silicon glue or with help of a mechanical fixture for proper temperature sense. The sensor senses the temperature, the output of the sensor rises as the temperature rise, and the comparator compares the sensor output with the threshold voltage of the PR1 trimmer potentiometer. When the sensor output is above the set point, LM358 provides a high output which triggers the MOSFET, and finally, the fan goes ON. The fan runs until the temperature drops less than the set point.
Features
- Supply 12V DC (Range 5V to 12V DC)
- Fan Load Up to 1Amp Continues (Maximum Load 4Amps)
- Temperature Threshold Range Adjustable 10 to 100 Degree Centigrade using Multiturn Trimmer Potentiometer.
- Simple and Low-Cost Temperature Management Solution for Heatsink or Equipment
- On-Board Trimmer Potentiometer to Adjust the Temperature Threshold
- PCB Dimensions 26.83 x 14.13 mm
Schematic
Parts List
| NO. | QNTY. | REF. | DESC. | MANUFACTURER | SUPPLIER | PART NO |
|---|---|---|---|---|---|---|
| 1 | 1 | CN1 | 2 PIN MALE HEADER PITCH 2.54MM | WURTH | DIGIKEY | 732-5315-ND |
| 2 | 1 | CN2 | LM35 | TI | DIGIKEY | LM35DZ/NOPB-ND |
| 3 | 1 | CN3 | 2 PIN MALE HEADER PITCH 2.54MM | WURTH | DIGIKEY | 732-5315-ND |
| 4 | 2 | C1,C3 | 10uF/25V SMD SIZE 1206 | YAGEO/MURATA | DIGIKEY | |
| 5 | 1 | C2 | 0.1uF/25V SMD SIZE 0805 | YAGEO/MURATA | DIGIKEY | |
| 6 | 1 | R2 | 1K 5% SMD SIZE 0805 | YAGEO/MURATA | DIGIKEY | |
| 7 | 1 | D2 | 1N4007 | SMC DIODE | DIGIKEY | 1655-1N4007FLCT-ND |
| 8 | 1 | D3 | DNP | |||
| 9 | 2 | R4 | 10K 5% SMD SIZE 0805 | YAGEO/MURATA | DIGIKEY | |
| 10 | 1 | Q1 | DMG3418L-7 | DIODE INC | DIGIKEY | DMG3418L-7DICT-ND |
| 11 | 1 | R1 | 75K 1% SMD SIZE 0805 | YAGEO/MURATA | DIGIKEY | |
| 12 | 1 | R3 | 470E 5% SMD SIZE 0805 | YAGEO/MURATA | DIGIKEY | |
| 13 | 1 | U1 | LM358 SOIC8 | ONSEMI | DIGIKEY | LM358ADR2GOSCT-ND |
| 14 | 1 | PR1 | 10K MULTITURN TRIMMER POT | BOURNS | DIGIKEY | 3296W-1-103RLFTR-ND |
| 15 | 1 | D1 | LED SMD SIZE 0805 | LITE ON INC | DIGIKEY | 160-1427-1-ND |
Connections
Gerber View
Photos
Video
LM358 Datasheet
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PCB
If I am not wrong, this circuit may have a problem
Suppose the trigger temp is set at 70deg. The fan shall be switched on at 70.1 deg and will switch off at 69.9 deg only to switch on again when the temp touches 70 deg. The cycle shall go on without much benefit.
The ideal situation is the circuit should switch on at the set temp and should switch off when the temp drops atleast 10 deg less than the set temp ( ideally to be set).