The Effects of Temperature on Transistor Performance

Image source Medium

When buying transistors, one of the parameters that you should check out is the operating temperature. This is the temperature range at which the transistor is expected to perform to the optimum levels. The range usually defines the transistor’s maximum and minimum temperature requirements. What will happen when I use the transistor outside the expected temperature regions? Will it get damaged or will there be a decline in the performance of the transistor? Kee reading as we discuss in detail the effects of temperature on the performance of the transistors.

Relationship between ambient temperature and breakdown voltage

To understand the effects of temperature on the performance of a transistor, it will be prudent that we establish the relationship between ambient temperature and the breakdown voltage.

Ambient temperature refers to the surrounding temperature. Let’s say you have installed the transistor in a room in a particular geographical area. The room temperature and that of the particular area will end up forming the ambient temperature.

Ambient temperature is usually denoted in terms of degrees Celsius or Fahrenheit (F). It is possible to control the ambient temperature in an indoor setup for the sake of the transistor performance. On the other hand, there is very little that you can do when it comes to regulating outdoor temperature.

The breakdown voltage of a transistor refers to a certain voltage at which there is a sharp flow of electrons from the collector to the emitter of the transistor. There will be a mass leakage of current when you exceed the breakdown voltage. This may end up damaging the transistor and other electronic devices or components that are directly connected to the transistor.

Other than the power supply, there are other conditions that can prolong the breakdown voltage of the transistor. Conversely, applying a voltage that is lower than the breakdown voltage can also lead to current leakage.

High ambient temperature leads to the leakage of the electrons from the transistor. However, it does not have any impact on the breakdown voltage of the transistor.

The image below illustrates the relationship between the breakdown voltage and the ambient temperature.

Image source Toshiba Semiconductors

Thermal stability of junction transistors

For all the transistors, there is always an effort to attain maximum temperature stability.  The stability ensures that the transistor operates at optimum levels without its performance being affected by drastic temperature changes. Increasing the temperature of the junction transistor will increase the collector current.

Usually, thermal instability in transistors occurs when both the junction temperature and the collector current increase in uncontrolled ways such that the transistor is unable to handle such uncontrolled changes.

There are several factors that affect the thermal stability of transistors. Some of these factors are internal while others are external. Current amplification and internal resistance are some of the internal factors that affect stability. Key external factors include the ambient temperature, power supply to the circuit, and thermal coupling between the transistors.

Most of the internal factors are controlled and regulated during the manufacturing of the transistors. On the other hand, external factors are regulated when the transistors are deployed to be used. Thermal stability has a direct impact on other aspects of transistors among them is the power dissipation of the transistor.

What are the effects of increasing temperature on the FET

Field-effect transistors (FET) are types of transistors whose resistance which defines the output current can be controlled by the field-generated input. An increase in temperature will directly impact the output current that is coming out of the field effect transistor.

One effect of temperature on the FET is it changes the value of the threshold Voltage (Vth). This is the voltage that kickstarts the flow of electrons between the source and the drain of the transistor. This voltage is usually supplied at the gate of the transistor. An increase in temperature is indirectly proportional to the threshold voltage. The higher the temperature, the lower the threshold voltage. This will eventually affect the biasing performance of the transistor.

Additionally, high temperatures tend to lower the breakdown voltage of the FET transistors. This means that it will require lower power to trigger an electrical breakdown in the transistor.

Speed of action

One common important application of transistors is switching. They are used as switches thanks to their fast reaction speed. Applications such as integrated circuits and as well as logical circuits rely on the switching speed of the transistors. So, what is the impact of temperature on the switching speed of the transistors?

Based on the general behavior of the electrons to heat, is clear that high temperatures increase the mobility of the electrons. So, we can only expect that the transistors will have a faster switching time when the temperatures are high to a certain level. However, beyond a specific threshold, the heat will increase the resistance to the conductivity and this will end up slowing the switching speed of the transistors. In some cases, extremely high temperatures can damage the structural composition of the semiconductors used for making transistors.

Changing the resistance of the transistor

Resistance is a key feature that ends up determining the performance of the transistors. On the other hand, there is a direct link between the resistance of a material and the temperature changes.

In most cases, an increase in temperature will increase the resistance of the transistors. This is likely to lead to a higher dissipation of power by the transistor leading to lower performance.

Other than the above power-related factors temperature has a direct impact on the reliability of the transistors. Exposing transistors to the extreme ends of the temperature ranges will lower their reliability index. This is possible because some components are likely to get damaged.

Conclusion

Now you know the impact of temperature on the performance of the transistors. You will be able to make the right decisions when it comes to protecting transistors from the negative effects of temperature. Also, buying high-quality transistors will be a smart move to get the best performance from the transistors.

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