What does a transistor do when F too High?

Discussion in 'General Electronics Chat' started by Dynaman, Nov 24, 2009.

  1. Dynaman

    Thread Starter AAC Fanatic!

    Jan 17, 2008
    Happy Thanksgiving All:

    I have a question regarding transistors and frequency in general. Let's say you have a small signal 2NXXXX transistor, and it is rated for 1.5Mhz max.

    If the signal amplitude applied to an amplifier or switching circuit were small signal,and the frequency surpassed it's rating, would the transistor burn out or just attenuate the signal and cease working until the F is reduced?

    Okay... now what if it were fed into a high powered transistor such as a T03 packaged device?

    Just Curious about what would happen. I don't have a signal generator that goes high enough to do the experiment.

  2. Papabravo


    Feb 24, 2006
    The output fails to follow the input.
  3. Audioguru


    Dec 20, 2007
    At the Transition Frequency, fT or the Gain-bandwidth product frequency the hfe (AC current gain) is 1. Above it the hfe is less than 1.
  4. Dynaman

    Thread Starter AAC Fanatic!

    Jan 17, 2008
    With no damage at low signal levels I suppose.. Correct?

  5. studiot

    AAC Fanatic!

    Nov 9, 2007
    A transistor does not suffer damage from signals that are beyond its frequency capability.

    It simply does not respond to them. In fact its response degrades progressively as frequency increases until it posesses no response at the transition frequency.

    There is a situation where a transistor can destroy itself by (high frequency) oscillation if it is incorrectly configured. However this frequency is still within the transistor's operating range, just usually outside the range of signal frequency of interest.
  6. lmartinez

    Active Member

    Mar 8, 2009
    To assist you with your question, I am quoting the following:

    "If the GBWP of an op-amp is 1 MHz, it means that the gain of the device falls to unity at 1 MHz. Hence, when the device is wired for unity gain, it will work up to 1 MHz (GBW product = gain x bandwidth, therefore if BW = 1 MHz, gain = 1) without excessively distorting the signal. The same device when wired for a gain of 10 will work only up to 100 kHz, in accordance with the GBW product formula. Further, if the minimum frequency of operation is 1 Hz, then the maximum gain that can be extracted from the device is 1 x 106".

    This information can be found at: