How To Use Diode As Temperature Sensor

Temperature Sensor

In this Temperature Alarm the 4007 diode is used as the sensor instead of the Temperature Sensor. The alarm sounds when the diode is heated.

Temperature Sensor Circuit Diagram :

Components Needed :

  • BC547 Transistor – 2
  • 1M Resistor – 1
  • 220 ohms Resistor – 1
  • Buzzer – 1
  • 1N4007 Diode – 1

Tools Needed :

  • Soldering Iron
  • Soldering iron Stand
  • Past
  • Lead
  • Cutter

Diode Working Principle :

diodes have numerous applications across the electronic industry and they are an integral part of any electronic device. in this Post we will explore the inner workings and applications of the diode in great detail basically a diode is a one-way valve for electricity let’s take a look at the internal structure of a diode the diode is made of a semiconductor such as silicon pure silicon does not have any free electrons but the silicon used here is not pure one part is doped with n-type impurity and the other part is doped with p-type impurity so at the end side of the diode we will have free electrons and at the P side we will have vacant positions for electrons something very interesting happens at the pn junction of the diode the abundant electrons on the inside have a natural tendency to migrate to the holes that are available on the p side so the P side boundary is slightly negatively charged and the N side boundary is slightly positively charged.

you can see the depletion region that is created the resulting electric field will oppose any further natural migration of electrons in short it builds a potential barrier for electron flow if you apply an external power source across the diode as shown the power source will attract the electrons and holes electricity flow is impossible in this case this condition is known as reverse bias of the diode you can see that the width of the depletion region increases here however if you connect positive terminal of the power source to the P side of the diode the situation is quite different assume that the power source has enough voltage to overcome the barrier potential you can immediately see that the electrons will be pushed away by the negative terminal when the electrons cross the potential barrier they will be drained of energy and will easily occupy the holes in the P region but due to the attraction of the positive terminal these electrons can now jump to the holes nearby in the P region and flow through the external circuit this is known as the forward biasing of a diode simply put a diode acts like a one-way valve for the flow of electricity now let’s vary the input voltage and study the diodes response to it in reverse voltage as explained you can observe a negligible electricity flow in the forward condition up to 0.7 volt you will find a negligible electricity flow but right after crossing this barrier potential value there will be a steep increase in the current flow however you can note that voltage across the diode does not go much higher than 0.7 volts even with high input voltage this is due to in forward biased condition the diode offers very low resistance against the current flow at the reverse-biased side applying a very high voltage will damage normal diodes and result in a high current flow the one-way electricity flow that is characteristic of the diode leads to interesting applications like a bridge rectifier during the positive half the circuit will conduct as shown the other two dials will be in a reversed biased state the negative half the reverse will be the case so we will get the same current flow direction at the output we can further smooth this output by introducing a capacitive filter

Temperature Sensor Working :

In this circuit conductivity is formed between the anode and the cathode when the diode is heated. So the NPN Transistor acts like Switching and makes the buzzer sound. Thus a diode is used as a temperature sensor.

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