How To Use Transistors For Temperature Control?

Image source Freepik

There are different electronic devices that are used for controlling or regulating temperature. When it is too hot, the device is programmed to lower the temperature; when it is too cold, the device can increase the temperature. These devices and gadgets have built-in working mechanisms that make them suitable for the temperature control functionalities.

Various electronic components connected to each other are also responsible for the temperature control functionality of such applications. Transistors are among the components that are used for executing temperature control. In this article, we are going to discuss ways in which transistors can be used for temperature control.

Overview of transistors and temperature

For years, there are transistors that have been used for temperature-related applications. These are called thermistors and are used for monitoring and sensing temperature changes in electric applications. But, do you know that you can use an ordinary transistor for the same applications or even more?

Other than sensing the temperatures, you can go ahead and use the transistor for regulating or controlling temperature. Of course, this is derived from the ability of the transistor to sense temperature changes. You may be surprised that semiconductor transistors will do a better job than a thermistor.

How is this possible? Well, the working mechanism of a semiconductor device is directly affected by the temperature changes. This property or mechanism is then translated into a real-world application where the same semiconductor will be used for regulating temperature.

Usually, an increase in temperature on a semiconductor material will initiate the forward voltage characteristics whereby there will be an increase in the movement of the electrons. The reverse will be true with a decrease in temperature. In other words, temperature has a direct impact on the flow of voltage and current across the junctions of the transistors. This property is heavily exploited whenever transistors are used for temperature control and regulation.

What makes transistors suitable for the temperature control applications?

As we have already mentioned, the suitability of the transistors is mainly because of the relationship between the temperature and voltage characteristics of the semiconductor material. But there is more to that.

One of the reasons is the linearity of the transistors in response to the temperature changes.  This simply means that the response of the transistors is accurate and more predictable as compared to the way thermistors respond to temperature changes. With linearity, a small adjustment on the transistor will have an instant impact on the temperature changes.

A graph showing the relationship between temperature vs current and voltage: Image source Electric Engineering stack Exchange

Another advantage of using transistors for temperature control is energy efficiency.  This is achieved due to the fact that transistors are designed to operate within defined regions namely active regions and saturation regions. High efficiency means that there will be minimal wastage of energy in the form of heat in your application.

What about the physical advantage of transistors? This is another major advantage of using transistors for temperature control and regulation. The compact design of the transistor makes it easy to be integrated into the circuits.

Fast switching speed is another major feature that makes transistors suitable for temperature control applications. A slight change in temperature conditions will trigger a quick response on the transistors. This feature is important in heat-sensitive applications where you have to bring all the temperature fluctuations under control.

Also, transistors are suitable for temperature control applications due to their ability to handle both the analog and digital signals. Whether you are building an analog or digital circuit, it will still work perfectly with the transistors.

Using transistors for temperature control

Now that you know the reasons why transistors are used for temperature control and regulation, let’s discuss how they are used.

Transistor temperature transducer

A temperature transducer is an electric device that is used for measuring temperature of a physical object. This device has the capability of converting the physical measurements or properties of an object to electric signals. This is where the importance of a transistor comes in. It translates thermal measurements into electric signals that will be translated and processed to influence necessary temperature control measures.

Technically, all types of transistors can be used as temperature transducers. However, BJTs are the most common types of transistors that are used as transducers. This is because their response to the temperature changes is more linear than other types of transistors.

Transistor as a temperature sensor

When using a transistor as a transducer, we have to take into account the temperature-sensing property of transistors. To achieve this, the transistor must be in a NPN configuration. Usually two transistors enclosed in a single case are used in an electric circuit. Input current is applied at the emitter terminals of the two transistors.

An operational amplifier (OpAmp) is usually included in this circuit to magnify the output signals. This way, the transistors will be more sensitive to the  slightest temperature changes. With the OpAmp, the circuit will be able to achieve a response change of as small as 10mV per degrees Celsius. Of course, the OpAmp should have a significant gain to achieve such levels of sensitivity.

When using a BJT transistor for temperatures sensor, ensure that it is put in a proper housing to protect it from external effects of temperature changes. A metal tube may be an appropriate housing for the transistor.

Two DC sources are connected to the two NPN BJT transistors and they serve as reference voltages. The reference voltage sources are connected to the collector-base pinouts of the BJT transistors. With this connection, it means that the emitter current from the transistor will be directly proportional to the temperature changes. This is because the collector voltage will always be constant.

The circuit should also have a potentiometer whose main function is to regulate the flow of current through the resistor. It regulates the flow of current in relation to the constant temperature changes.

This image from Homemade-Circuits will give you a better explanation of how the  transistor temperature sensor works.

There you have it! Now you know that it is possible to use transistors for temperature control. The next step is buying quality transistors from reputable distributors and sourcing agents in China.

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