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Simple temperature indicator circuit design electronic project

This simple and inexpensive temperature indicator indicates the temperature of a heat sink in high power circuits can be designed using this electronic circuit diagram.
Temperature is measured by a transistor mounted on a radiator or near power transistor controlled.
T1 temperature sensor and voltage to the base - emitter is compared, through potentiometer P1, with the common point of reference in its D1 and R1. Transistor remains blocked as long as temperature remains below a certain level, which is set to P1. Base-emitter voltage of transistor will decrease by about 2 mV for a temperature increase of about 1 ° C. When the emitter voltage of transistor voltage falls below the cursor P1, the transistor will go into conduction and D2 will light.
The values of R1 and R2 are voltage dependence of Ub dente and relationships can be calculated:
R1 = [(Ub - 0.6) / 5] k, R2 = [(Ub - 1.5) / 15] k

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Simple temperature indicator circuit design electronic project