Voltage dropping resistors

Discussion in 'General Electronics Chat' started by hobbyist, Sep 2, 2008.

  1. hobbyist

    Thread Starter Distinguished Member

    Aug 10, 2008
    Something I learned this evening while working on my project,

    That when I use a series dropping resistor to drop the Vin. to a lower voltage for the base input to the transistor DC. amp. that not only does the dc voltage drop. but also the "change in output voltage with respect to input voltage drops as well"

    I wanted to amplify a dc. volt. drop 40 millivolts. across a load resistor.

    Instead of getting my Av 5 that I designed it for I got Av 1.5,
    after further investigation I realized I was getting Av 5 from base input to collector output, but from the other end of the series resistor I was only getting a Av. of 1.5.

    The large series resistor will in fact drop the "change in voltage as well"

    After doing the math I realized the ratio of Vin/Vo across a series resistor with another resistor to ground is the same ratio as the change in Vin/Vo across the resistor.
    The Vo side of the resistor has a resistor to ground.

    So using this info. I can determine the amount of gain needed to compensate for a signal loss through a needed series resistance.

    Boy do I feel st....pd

    Itis nothing more than signal attenuation.
    Just that I was looking at it from Dc signal, and forgot that it is a attenuator...

    Oh well...
    Last edited: Sep 2, 2008
  2. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    Post the schematic. Someone may have a way of avoiding the attenuation in the first place.
  3. hobbyist

    Thread Starter Distinguished Member

    Aug 10, 2008
    I would but I can't seem to get anything to show up after its uploaded.