Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Transition frequency

  1. May 27, 2010 #1

    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?

  2. jcsd
  3. May 27, 2010 #2
    http://cktse.eie.polyu.edu.hk/eie304/FrequencyResponse.pdf [Broken]
    Last edited by a moderator: May 4, 2017
  4. May 27, 2010 #3
    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

    Attached Files:

  5. May 27, 2010 #4
    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?
  6. May 28, 2010 #5
    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
  7. May 28, 2010 #6
    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.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook