---
+ Post New Thread
Results 1 to 4 of 4
  1. #1
    Full Member level 1
    Points: 965, Level: 7

    Join Date
    Oct 2010
    Posts
    117
    Helped
    0 / 0
    Points
    965
    Level
    7

    Question about BJT in saturation

    Hi,
    i have some question about biasing the bjt into saturation, and its switch configuration
    1. Is it necessary to have Vce <= 0.2 in order for bjt to saturate?
    2. So what if a very low resistive load is connected to it, since I think usually it will then have Vce greater than 0.2, so that means bjt can never be saturated under low load condition?
    3. is the switch configuration is just common emitter?
    4. can I have the bjt as a switch in emitter follower?

    your help will be greatly appreciated!
    Last edited by hayowazzup; 5th August 2011 at 15:31.

    •   Alt5th August 2011, 13:41

      advertising

        
       

  2. #2
    Advanced Member level 4
    Points: 16,694, Level: 31
    kak111's Avatar
    Join Date
    Mar 2011
    Location
    Finland
    Posts
    1,376
    Helped
    934 / 934
    Points
    16,694
    Level
    31
    Blog Entries
    8

    Re: Question about BJT in saturation

    Answer: 1&2

    bjt_saturation_zone.jpg

    Answer: 3&4

    We can say that BJT act as switch , if it works only in cutoff and saturation states.

    Transistor Switches
    ---> Hike with wise men , then you will be wise <---



    •   Alt5th August 2011, 14:58

      advertising

        
       

  3. #3
    Newbie level 4
    Points: 783, Level: 6

    Join Date
    Sep 2008
    Posts
    6
    Helped
    2 / 2
    Points
    783
    Level
    6

    Re: Question about BJT in saturation

    1. Not necessary
    2. saturation is the condition Ic< Beta *iB
    3. yes with Rc* Beta > Rb
    4 yes switch is on when base is tied to vcc ; off when base is tied to ground



    •   Alt5th August 2011, 15:03

      advertising

        
       

  4. #4
    Super Moderator
    Points: 36,763, Level: 46
    Achievements:
    Created Album picturesCreated Blog entry7 years registered
    alexan_e's Avatar
    Join Date
    Mar 2008
    Location
    Greece
    Posts
    11,347
    Helped
    2037 / 2037
    Points
    36,763
    Level
    46
    Blog Entries
    6

    Re: Question about BJT in saturation

    Quote Originally Posted by hayowazzup View Post
    Hi,
    1. Is it necessary to have Vce <= 0.2 in order for bjt to saturate?
    You don't set the Vce to saturate but you have a low Vce as a result of the saturation, the Vce level is not exact it can be higher too

    Quote Originally Posted by hayowazzup View Post
    2. So what if a very low resistive load is connected to it, since I think usually it will then have Vce greater than 0.2, so that means bjt can never be saturated under low low condition?
    Again the low Vce is not a requirement for the transistor to saturate but the result of a saturated transistor, the Vce voltage can have a higher level too.

    Quote Originally Posted by hayowazzup View Post
    3. is the switch configuration is just common emitter?
    4. can I have the bjt as a switch in emitter follower?
    You can either have the load connected to the collector or the emitter.
    When the load is connected to the collector then you can control a load that has a higher voltage then the base.
    When the output is the emitter then the output will always have a 0.7v difference from the base, so for example with a 5v to the base of a NPN you will only get 4.3v to the emitter ot with 0v to the base of a PNP you will get 0.7v to the emitter.

    Alex
    Please don't make requests for help in private using PM. Create a thread in the forum so that other members can benefit from the posted answers.

    Consider reading this before posting : How To Ask Questions The Smart Way



+ Post New Thread
Please login