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  • BJTs

    gargoor

    Member

    Updated: Oct 26, 2024
    Views: 1.0K
    Hello buddies am back again wit more doubts as usual leaning on you ppl to lift me up a lil more

    Bipolar junction transistors

    Saturation Level ( Ic,sat)
    what is the point of calculating the saturation level of a transistor ?
    i totally can count it but practically i want to know what can it help for ?

    Q-point (queiscent level?
    it's known around that the purpose behind dc analysis for BJT's that is to figuer the Q-point of it ? well the confusion here is that i couldn't get what q-point is ? and what it stands for? had lots of graphs wich shows the q point but i have questions marks on my head everytime i try to know what's it i get more question marks ,,

    BJT's transistor are one of the common used as far as i know but is there any big difference between this catagory and other catagories of transistors?
    and what are the other catagories wich an engineer MUST know ?
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  • reachrkata

    Member • Apr 14, 2009

    Considering a simple CE amplifier configuration -

    Determining the Icsat will give you an idea of how much Ibsat you would need. Note here that Icsat would depend on the collector resistor you have used.
    I can think of no other use.

    For the same CE amp, consider that you are using one for an AC signal amplification. Since you would normally not have -ve voltage sources, you would connect the emitter of the transistor to GND. Now since your input signal is a sine, you would have to bias the transistor so that it provides the necessary DC offset for the signal.
    Having chosen the offset level you would have to design the amplifier in such a way that the (DC offset + the positive peak of the sine) doesnot cause the transistor to enter into saturation and (DC offset - the negative peak of the sine) doesnot cause the transistor to enter into cut-off. This is important if you want to have a pure sine amplified output for the sine input. This process of designing is called finding the Q point of the circuit.

    Putting it in other words, if you have only the DC bias as input for the transistor, the output amplified DC level should be such that the transistor always remains in the active region for the required sine input that you provide.

    Hope this clarifies.

    Cheers
    Karthik
    😁
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