# How you know to choose BJT transistor or MOSFET for you Tesla Coil circuit

#### reyfonal21

Joined Aug 15, 2022
2
Hello, people! Thanks for the dropping. I made a Tesla Coil with oscillator circuit on it for project in school and it work well. But I want know how to choose ideal BJT/MOSFET transistor for the transmitter. Is there any reason, formula, or theory that I should know? Because Youtube and other article didn't give much explanation on it

#### Papabravo

Joined Feb 24, 2006
18,978
Hello, people! Thanks for the dropping. I made a Tesla Coil with oscillator circuit on it for project in school and it work well. But I want know how to choose ideal BJT/MOSFET transistor for the transmitter. Is there any reason, formula, or theory that I should know? Because Youtube and other article didn't give much explanation on it
There is a great deal of information that will be useful to have. Accumulating and assimilating that information may take a while depending on your background. Understanding AC circuits generally happens in the 3rd year of an undergraduate engineering curriculum. Are you anywhere close to that level of accomplishment?

#### reyfonal21

Joined Aug 15, 2022
2
I am in engineering machine major at vocational university for three years (also this will be my last year of college). So I hope I can understand well what will you inform. And sorry for weird English since its not my mother languange

#### Papabravo

Joined Feb 24, 2006
18,978
If you are familiar with transistor datasheets, you should be aware that multiple characteristics of the device are described. Aside from the maximum voltages and currents that can be handled, some knowledge of the gain characteristics as a function of frequency will be useful in your application. The parameter of interest is called $$F_{T}$$, and it is the frequency for which the gain is unity. See the following article for additional information.
https://community.cadence.com/cadence_blogs_8/b/rf/posts/measuring-transistor-ft#:~:text=First, let’s review the meaning of ft. It,transistor will be connected to a power supply.
The following simulation, from @Bordodynov, shows a transistor (2SC2395) with a unity gain frequency at approximately 200 MHz.

It may not be convenient to select from the set of all transistors that have ever been produced. In many cases it will come down to what is available and what you can afford. My experience from 20 years ago is probably irrelevant in today's environment.