Personal opinion about a part of the e-book

Discussion in 'Feedback and Suggestions' started by mik3, Dec 4, 2008.

  1. mik3

    Thread Starter Senior Member

    Feb 4, 2008
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    This is a text part of the Static Electricity Sensor experiment:

    'The fact that a JFET is turned on and off so easily (requiring so little control current), as evidenced by full on-and-off control simply by conduction of a control current through your body, demonstrates how great of a current gain it has. With the BJT "switch" experiment, a much more "solid" connection between the transistor's gate terminal and a source of voltage was needed to turn it on. Not so with the JFET. In fact, the mere presence of static electricity can turn it on and off at a distance.'

    It says that JFETs have current gain (bolded). I don't agree with this term. Current gain means the output current divided by the input current. Since JFETs draw very little current, in my opinion, its not correct to say they have current gain. Instead, they have transconductance (Iout/Vin). Also, BJTs have greater transconductance than JFETs because the same amount of change in input voltage causes a larger change in output current for BJTs. The fact that JFETs are more sensitive is due to their high input impedance (draw very little current).
     
  2. mik3

    Thread Starter Senior Member

    Feb 4, 2008
    4,846
    63
    I am sorry I posted in the General Electronics chat room about this topic but I did not see the Feedback and Suggestions chat room.
     
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