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# LM56 Thermostat Project Circuit Diagram

This electronic circuit thermostat using IC LM56 diagram which simple project you can use as reference guide. As you know, IC LM56 is especially accurate dual output low power thermostat characterize by National Semiconductors. 2 stable temperature trip points called VT1 and VT2 are made with dividing the IC LM56 1.250Volt internal voltage reference by three external resistors (R1, R2 and R3) component. There are 2 digital outputs for IC LM56 that is Output1 becomes LOW when the temperature increases above T1 and goes HIGH when the temperature decreases below (T1±Hysteresis Temperature). Component IC LM56 has a variety of useful features such as internal temperature sensor, 2 internal voltage comparators, internal voltage reference etc.

The circuit diagram thermostat using IC LM56 values of R1, R2 and R3 for the required trip points VT1 and VT2 can be determined using the subsequent equations.

VT1 = 1.250V x (R1)/ (R1 + R2 + R3)
VT2 = 1.250V x (R1 + R2)/ (R1 + R2 + R3)
where:
(R1 + R2 + R3) = 27 k Ohms and
VT1 or T2 = [6.20 mV/degree Celsius x T] = 395 mV therefore:
R1 = VT1/ (1.25V) x 27 k Ohms
R2 = (VT2/ (1.25V) x 27 k Ohms) – R1
R3 = 27 k Ohms – R1 – R2