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Linearization circuit of thermistance

2017-03-11 14:12  
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Linearization circuit of thermistance
This diagram is Linearization circuit of thermistance. In the circuit, it also is constant flow source. Its non-inverting input end is offered reference voltage by 78LO5. The output of A2 offers constant current for thermistance RT. This current is connected ground through R1. The value of constant current is determined by R1. If RT is 5kΩ, constant current is 120μA when the voltage dropping on RT must be 0.6V. This voltage dropping adds to the source of VT1 through A3 buffer. Because the grid of VT1 is connected in one side of RT, so, grid-source voltage of VT1 is the voltage on the justified of RT. The function of R2 is flowing through idle current. The output voltage of A3 can remain unchanged when source current of VT1 changes. The justified voltage of R3 and temperature is linear relation. But R3 is in the state of floating. So, differential amplifier A4 offers this voltage. The relation between output voltage Uo and temperature changes to linear relation.