Transcript Document

INDEPENDENT
PROJECT
RITAMBHARA CHAUHAN-ES12B1015
SAVIT VARCHASVI ALURI-ES12B1017
Indian Institute of Technology
Hyderabad
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!!!!!!