Transition Frequency of 2N2222A Transistor - Explained

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Discussion Overview

The discussion centers around the concept of "transition frequency" in the context of the 2N2222A transistor, particularly regarding its application in switching functions for a motor controlled by a microcontroller. Participants explore the implications of transition frequency on performance and suitability for specific applications.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant inquires about the meaning of "transition frequency" and its importance in using the 2N2222A for switching applications.
  • Another participant provides a link to a document that may contain relevant information about frequency response.
  • A participant explains that the transition frequency (fT) is the frequency at which the gain of the transistor is unity and emphasizes that for fast switching, the transistor should not enter saturation.
  • Concerns are raised about the suitability of the 2N2222A for switching applications, with a suggestion that other transistors may be better suited for faster switching.
  • Questions are posed regarding the specific voltage and current requirements for the application, as well as the timing requirements for switching.
  • It is noted that if the switching frequency is close to fT, the quality of the switching waveforms may be compromised, affecting the duty cycle.

Areas of Agreement / Disagreement

Participants express differing views on the suitability of the 2N2222A for the intended application, with some suggesting it may not be the best choice compared to other transistors. The discussion remains unresolved regarding the optimal choice of transistor based on specific application requirements.

Contextual Notes

Participants highlight the need for clarity on voltage, current, and timing requirements to assess the appropriateness of the 2N2222A. There is an acknowledgment that the transition frequency's impact on switching performance is contingent on these factors.

ws0619
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Hi!

I saw this words "transition frequency" in the 2N2222A transistor data sheet.f=100MHz. What's this actually?

I want to use this transistor 2N2222A to act as a switching application for turning on the motor by using microcontroller.
So what should I consider when using this transistor? Is it transition frequency important to be consider?Can someone please explain for me?

Thanks!
 
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http://cktse.eie.polyu.edu.hk/eie304/FrequencyResponse.pdf
 
Last edited by a moderator:
Here attached is the 2N2222 datasheet.

fT is the unity-gain-bandwidth product, the frequency at which the gain is unity.

For fast switching, the transistor should not be allowed to go into saturation. The configuration I have used is a differential pair with a long tail (high resistance common emitter resistor to Vee). In reading between the lines in the data sheet, the best choice for Vce and Ic is probably 20 volts and 20 mA. Why do you want to use the 2N2222?

Bob S
 

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Because I need a switching function of transistor, and what I learned just on theory about transistor.I don't know what transistor to use, so I just google for the switching transistor and I get this type of transistor.
Is it not suitable to use 2N2222?
 
What voltage and current would you like to use? There are many faster switching RF transistors, especially with lower optimum switching voltage and currents. I have used the 2N5770 (@ 10 volts, 8 mA) a lot for fast risetime switching.

Bob S
 
To address whether the 2N2222, is suitable for your use, we need to understand your voltage and current requirements, and your switching timing requirements.

How frequently is a full transition required (from on to off to on)?

Is there a requirement for how fast a turn on must be completed, or for how much delay can be tolerated from a change in base control voltage to a change in collector current?

If the switching frequency is within a few octaves of Ft, the squareness of the switching waveforms will be compromised, as may the duty cycle. Generally good "squareness" requires Ft to be a lot higher than the fastest switching frequency.
 

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