Indian Institute of TechnologyHyderabad

INDEPENDENT PROJECT

RITAMBHARA CHAUHAN-ES12B1015SAVIT VARCHASVI ALURI-ES12B1017

Temperature Controlled Switch

Temperature controlled switch

Temperature controlled switch

When the LM35DZ(An IC included in a circuit) detects a temperature higher than a preset level, the LED is switched on.

So basically the circuit can be used in circuits where a device can be made operational or non-operational when temperature variations occur.

This is a circuit which can be used in applications where automatic temperature control is needed.

Components used IC1 :   LM35DZ  Precision Celsius (Centigrade) Temperature

sensor  IC2 :  TL431  +2.5V precision voltage reference IC3 :  LM358  Dual single supply Op-amp. 

LED1 -- 3mm or 5mm LED 

Q1 -- General purpose PNP transistor ( A1015,...) with E-C-B pin-out) D1, D2  -- 1N4148 silicon diodes (or 1SS133)D3, D4  -- 1N400x (x=2,,,,.7) rectifier diodes

ZD1 --- Zener diode,  13V, 400mW

Preset (trim pot) :  2.2K   (Temperature set point)                           (# 222 or  2k2)

Components used Resistor  : ( 1/4W or 1/6W)R1 -- 10K    R2 -- 4.7M R3 -- 1.2K R4 -- 1K R5 -- 1K R6 -- 33Ω Capacitors : C1  -- 0.1 µF ceramic or mylar cap

         (# 104 or 100n)

Working…..The heart of the circuit is the LM35DZ temperature

sensor which is factory-calibrated in the Celsius (or Centigrade) scale with a linearDegree->Volt conversion function.

The output voltage (at pin 2)  changes linearly with temperature from 0V  (0oC)  to  1000mV (100oC). This greatly simplifies the circuit design as we only need to provide a precision voltage reference (TL431) and an accurate comparator (A1 of LM358) in order to construct a complete thermal-controlled switch.

Working…. The preset (VR1) & resistor (R3) from a variable voltage

divider which sets a reference voltage (Vref) form 0V ~ 1.62V. The op-amp (A2) buffers the reference voltage so as to avoid loading the divider network (VR1 & R3).  The comparator (A1) compares the reference voltage Vref  (set by VR1) with the output voltage of LM35DZ and decides whether to switch on or switch off the LED.

We can set a specific temperature according to our wish with the help of voltage across the variable resistor.

When the temperature in the surroundings is higher then a specific value, then it gets switched on. And when temperature is again low it is switched off.

Temperature controlled switch…

Thank You!!!!!!