It is a simple design circuit for thermistor triggered switch using adjustable threshold. This circuit is triggered with cold temperatures that may be used as frosh alarm or cold temperatures switching. This circuit working with based on op-amp 741. This is the figure of the circuit.
In this circuit, temperature that is used resistance of 15k at 25 degrees Celsius and 45k at 0 degrees Celsius. For operation the circuit, it is begin with function of the op-amp. In this circuit, the op-amp is used as comparator. Pin 3 in the op-amp is used as biased to half the supply voltage. The non-inverting input is connected to the junction of the thermistor and potentiometer. The control is adjusted so that the circuit is on when the thermistor is at the required temperature range. A slight amount of hysteresis is provided by inclusion of the 270k resistor. This prevents rapid switching of the circuit when the temperature is near to the switching threshold.
In this circuit, temperature that is used resistance of 15k at 25 degrees Celsius and 45k at 0 degrees Celsius. For operation the circuit, it is begin with function of the op-amp. In this circuit, the op-amp is used as comparator. Pin 3 in the op-amp is used as biased to half the supply voltage. The non-inverting input is connected to the junction of the thermistor and potentiometer. The control is adjusted so that the circuit is on when the thermistor is at the required temperature range. A slight amount of hysteresis is provided by inclusion of the 270k resistor. This prevents rapid switching of the circuit when the temperature is near to the switching threshold.
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