PC Temperature Controller

  Here is a simple temperature controller that turns your
personnel computer (PC) off when the temperature of the PC
increases beyond the optimal temperature value. Some of the larger integrated
circuits become quite hot and if the temperature inside the PC becomes 
too high, these devices may not be able to dissipate heat fast enough. This, in
turn, could lead to failure of devices and eventually of the PC.

to prepare PC Temperature Controller...we need

• TRIAC
• Bridge rectifier
• IC's IC LM35 ,IC CA3140
• Zener diode
• resistor 
• capacitor

Let us assume that the maximum working temperature of your PC is
55°C. So for safe working of your PC, this temperature controller uses
a temperature sensor (LM35) and a comparator (CA3140) which disconnect
the PC from the power supply whenever the temperature of your PC
rises above 55°C. This threshold value is user-adjustable and can be set
anywhere between 0°C and 100°C. Fig. 1 shows the circuit of the PC
temperature controller, while Fig. 2 shows pin configurations of the components
used. The circuit works off 9V DC, which is derived from main
power as follows: Mains power supply is rectified by a bridge rectifier
comprising diodes D1 through D4, divided by a resistor network comprising
R1 and R2, and stabilised by zener diode ZD1. Capacitor C1 filters
the ripples.
         Using preset VR1 you can set the reference voltage. The reference
voltage at non-inverting pin 3 of the comparator is set such that the temperature
of the PC is 55°C. When the temperature of the PC is below 55°C,
the voltage at the inverting input (pin 2) of IC2 is lower than the voltage at
the non-inverting input (pin 3). At this stage, the comparator output at pin 6
of IC2 is high. This high output triggers triac 1 (BT136), providing mains
power to operate the PC.
        When the temperature of the PC increases above 55°C, the inverting
input (pin 2) of IC2 also goes above the non-inverting input (reference
voltage) at pin 3 and hence the comparator output goes low. This stops
triggering of triac 1 (BT136) preventing mains power supply from reaching
the PC.
        Thus this arrangement provides mains voltage to the PC at temperature
of up to 55°C and stops when the temperature goes above 55°C.
Assemble the circuit on any general- purpose PCB in the form of a PC
expansion card, so you can use it as an add-on card to any PC. Plug it in,
switch-on the supply and use your computer with safety temperature
device.

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