My new house theatre receiver used to be getting relatively scorching in the shut confines of its cabinet, with the temperature attaining over 40°C after handiest about half-hour of use. To lend a hand lower the temperature, I decided to install a fan within the cabinet. A 75mm hole used to be lower in the shelf beneath the receiver, and a 12V fan salvaged from an outdated computer energy provide was installed beneath. The fan used to be powered from a 12V DC plugpack.
This did the job, maintaining the temperature under 30°C even after prolonged use on a heat day. However, the fan was once annoyingly loud when operating at full speed. To reduce the noise degree notably, I constructed this fan pace controller with temperature comments. The circuit was culled from number of concepts found on various websites on the web, with the final circuit designed from what was once within the \"junk box\". Air temperature in the cabinet is sensed via an LM335 (TS1).
Circuit diagram:
Junk-box Fan Speed Controller Circuit Diagram
It is glued to a section of aluminium about 25mm square with fast glue, which is then connected to the highest of the receiver with \"Blue-Tack\". About 300mm of audio coax makes the connection back to the circuit board. The LM335’s output upward pushs 10mV per diploma Centigrade. It is calibrated to zero output at -273°C, so at 20°C, the output will doubtless be 2.93V. This is applied to the non-inverting input of a 741 op amp (IC1). A 1N4733 5.1V Zener diode gives a voltage reference for the inverting input via trimpot VR1. The output of the op amp forces a TIP122 Darlington transistor (Q1), which in flip pressures the fan motor. The op amp gain was once calculated to provide about 12V to the fan at 40°C.
To keep the transistor cool, it's set up on the metal base of a small plastic field, which is also used to accommodate the elements. Initial setup will have to be carried out with everything turned off and the ambient temperature at about 20°C. Adjust the 10-turn pot except the fan just stops running. I used a gasket comprised of foam strips and \"blue-tacked\" them between the feet of the receiver to direct all the airflow by way of it. The temperature now remains at about 32°C, the fan runs very quietly and continues to run down for approximately 30 minutes after the receiver is switched off.
Author: Martin Cook - Copyright: Silicon Chip Electronics
