Many electronics circuits and projects for learning in simple ways.

Simple temperature sensor diode 1N4148

What is the temperature sensor diode? It is a general silicon diode. We will show how it works. When a diode is forward biased, the resistance of a diode changes with temperature.

Temperature sensor diode 1N4148-min

Usually, we have seen this type of equipment, a thermistor. It is a type of resistors and easy to use. But we do not see in normal using.

As above, In fact, we can use all semiconductor devices as a temperature sensor.

Inside semiconductors have resistances. Its resistances will reduce when it to be hot.
In the opposite way, when it is cold its resistance rises.

We can use many semiconductors, transistor, IC, SCR, and more. But this circuit uses the diodes, D1-1N4148. Because it is easy to use, cheap, see all-time in shop.

In fact, when the diode is in forward biased. It has voltage across about 400mV to 500mV at current about 1mA. This voltage level depends on the current and the substance used to generate these diodes.

In silicon diode, the voltage across it will reduce about 2mV in each one degree Celsius temperature.

We so can use it. Also, you can use a transistor, diode bridge and more. They are also silicon semiconductors.

In the circuit above is a simple temperature sensor diode, D1.

First, get a steady voltage power supply. The Dual +15V/-15V DC Regulator is suitable for here.
Second, a constant current comes to D1 through R1. When the temperature of D1 changes, the voltage across it changes, too.

But this changing makes voltage changes very very low. We cannot measure it on a normal voltmeter. We need a helping of the comparator.

Third, use op-amp comparator IC, LM741. We set it into a inverting compator mode.

Why use this mode?
Since we need to measure the output voltage and Temperature is in the same way.

For example, Temperature is 20 degree Celsius, it makes output voltage is 2.00V.
But the temperature rises up to 30 degrees Celsius, the output voltage should rise to 3.00V, too.

Thus, we use this mode.

When Vin (pin 2) exceeds Vref(pin3), output switches from High to Low.

You do not worry if you do not understand it. You do not need to know all about it. Just you can use it is enough.

Fourth, we need to use VR1 and VR2 to adjust a right of this temperature sensor diode.

Last, when setting you should use the Digital Thermometer to compare real temperature. A digital voltmeter you may have it. The importance, you take an ice, hot water. but Diode cannot touch the water.

This circuit is not accurate full 100%. It just is good for learning in the Science experiments. Have fun!

‘Keep Reading: Use this to be Differential temperature controller’ »

This Post Has 2 Comments

  1. I suppose the person giving the circuit description is not english for its also not my 1st language. I don’t understand the description.

  2. Hi, Arend
    Thanks for your visiting.
    I’m very sorry for poor English of us.
    But we will grow.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Close Menu