transistor voltage drop

Discussion in 'General Electronics Chat' started by alexmath, May 11, 2014.

  1. alexmath

    Thread Starter New Member

    May 2, 2014
    17
    0
    Hi. I don't quiet understand transistors.
    1) How the gain of the transistor is constant? If i get it into the saturation, and i change the voltage input that means that i have higher current flowing with the same base current.
    2) If there's no current through the base, why does transistor still drop voltage(about 1v)? Isn't it like an open circuit? I just blew up some transistors connecting them to 9v battery :D
    3) Another thing that i don't understand is why the forward voltage drop across an led is changing? I've got even 8-9v across an led of 3v... how is that possible? Shouldn't be the current across the circuit changing in function of what resistor i use and the voltage drop across the led to be the same? There are huge difference in voltage drop with differnt kind of resistors. :eek:

    Thank you!
     
  2. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    Show your circuit so we can have a better idea of what your concerns are.
     
  3. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    The gain of a transistor is not constant. I varies with collector current. And certainly if it goes into saturation, then obviously an increase in base current can have no further effect on the collector current.

    If you blew up the transistors then you connecting them incorrectly to the battery. Can't really help without a schematic of what you are doing.

    The LED forward drop does vary with current. It's just a logarithmic variation, not a linear variation.
     
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