Understanding a heat sensor circuit?

In summary, the β parameter of the npn transistor is temperature dependent, which means that increasing the temperature will also increase the collector current and turn on the LED. However, the purpose of the resistor arrangement and the use of a diode to keep the Base-Emitter junction in forward bias is not clear and may be counterproductive due to the temperature dependence of the diode's voltage. There is also confusion about what temperature is being measured and the overall goal of the circuit.
  • #1
Raihan amin
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TL;DR Summary
I am builiding a heat sensor circuit using this circuit model. But first I want to understand how this circuit is working.
Circuit link: https://circuitdigest.com/electronic-circuits/heat-sensor
What I understand is that the β parameter of the npn transistor is temperature dependent. Increasing the temperature increases the collector current and hence the LED turns ON. But I don't understand the resistor arrangement.Also I can see that the diode is keeping the Base-Emitter junction in forward bias. But why this is necessary? I believe the pot is supposed to maintain the sensitivity but how is it doing this?

Looking for some thoughtful explanation.
 
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  • #2
The use of the diode seems counter-productive to me, since its ## V_f ## is temperature dependent as well, and would seem to counter the temperature effect that they are trying to use the transistor for...
 
  • #3
Raihan amin said:
What I understand is that the β parameter of the npn transistor is temperature dependent.
It is not beta that is temperature sensitive, it is the base-emitter voltage.
I agree with @berkeman The reference is also a PN junction, namely the 1N4148, so it gets confusing as to what temperature is being measured, relative to what. Was it a failed attempt to build a bandgap reference?
 
  • #4
That circuit would work fine if you consider it a differential thermometer.
It reacts to the temperature difference between the diode and transistor.

Cheers,
Tom
 

Related to Understanding a heat sensor circuit?

1. How does a heat sensor circuit work?

A heat sensor circuit works by using a temperature-sensitive material, such as a thermistor, to detect changes in temperature. When the temperature changes, the resistance of the material also changes, which is then measured by the circuit. This information is then converted into an electrical signal that can be interpreted by the circuit.

2. What components are needed to build a heat sensor circuit?

The main components needed to build a heat sensor circuit include a temperature-sensitive material (such as a thermistor), a power source, a resistor, and a microcontroller or other circuitry to process the signal. Additional components may be needed depending on the specific design and function of the circuit.

3. How accurate is a heat sensor circuit?

The accuracy of a heat sensor circuit depends on the quality and precision of the components used, as well as the design and calibration of the circuit. In general, most heat sensor circuits have a high level of accuracy and can detect small changes in temperature.

4. Can a heat sensor circuit be used to control temperature?

Yes, a heat sensor circuit can be used to control temperature by using the electrical signal to activate a cooling or heating system. For example, the circuit could be connected to a fan or heater to turn on or off when a certain temperature threshold is reached.

5. Are there any safety concerns when using a heat sensor circuit?

Yes, there are some safety concerns when using a heat sensor circuit, especially if the circuit is being used to control temperature in a potentially hazardous environment. It is important to carefully design and test the circuit to ensure it is functioning properly and to follow all safety protocols when using the circuit.

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