Calculating Base Resistor on BJT

Discussion in 'General Electronics Chat' started by GioD, Oct 17, 2013.

  1. GioD

    Thread Starter Active Member

    Mar 20, 2009
    Moderator Note: This thread has been split from Calculating Base Resistor for a BJT

    I don't see in the diagram the resistor usually connected from Base to Emitter. What's the utility of this further resistor ? Is always necessary or not ?
    Last edited by a moderator: Oct 17, 2013
  2. slakku

    New Member

    Jul 27, 2011
    Hello minulescu,

    Regarding Beta, in most cases i have seen people using 20 for calculations., however it depends on which transistor (Parameter) you are using.
  3. wayneh


    Sep 9, 2010
    You've reopened a 5-1/2 year old thread. If you have a question on something, you should start your own thread.

    And no, this circuit doesn't need a resistor from emitter to base. If you supply an example of such an arrangement, someone here will explain it to you.
  4. crutschow


    Mar 14, 2008
    If you look at their data sheet, most BJTs are specified at a Beta of 10 for the Vce saturation voltage measurement, so that is why a value of 10 is commonly used when you want the transistor to be fully ON.

    Of course you can also use a logic-level MOSFET, which requires no gate current, to control the LEDs.