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Thursday, February 14, 2008


Temperature controlled fan is a circuit employed to vary the speed of the fan with respect to the surrounding temperature . If the room temperature decreases (increases), the speed of the fan automatically reduces (increases). To accomplish the control over the temperature, we employ a rectifier to convert the input ac current to the dc current, a linear potentiometer to control the resistance of the thermistor which in turn changes the input voltage of the transistors. The transistors act as control circuit and generates required signal for the SCR and based on this signal applied to the SCR, the speed of the fan varies. Thus by using minimum number of components we are able to achieve the required temperature control by varying the speed of the fan correspondingly. This model, along with a fan arrangement is used in central processing unit of the computer to prevent the over heating of the CPU. It can also be used in heating applications by reversing the circuit operation.

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