Transistor circuit for amplification

Discussion in 'The Projects Forum' started by jordon30, Oct 13, 2014.

  1. jordon30

    Thread Starter New Member

    Oct 13, 2014
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    0
    Hi,

    I have a 6v system that i wont to run off a 12v car battery, i looked at 6v regulator but the little ones i want cant handle more then 1A, which i don't believe to be enough. Im not very skilled at electronics but know most of the basics, I am wanting to use a transistor (possibly 2n3055) to power my 6v system which needs about 3-5amps(yet to confirm).

    I want to build something that wont be to big, and as it wont be running for very long periods at a time, less then 5 mins then a cool down period, the smaller the components the better i say!

    So basically i have drawn up a few designs using my limited knowledge and was after some guidance as to where i could improve and what i have to do to make things work.

    In my schematics i used a 12Vin 9Vout regulator and 2n3055 NPN transistor as i have theses at home.

    Any help will be appreciated.

    Thanks.
     
  2. #12

    Expert

    Nov 30, 2010
    16,261
    6,768
    Take a peek at these.
     
    flat5 and Johann like this.
  3. jordon30

    Thread Starter New Member

    Oct 13, 2014
    3
    0
    Thanks! Will see if i can get it working tonight.
     
  4. jordon30

    Thread Starter New Member

    Oct 13, 2014
    3
    0
    #12

    I tried the first schematic last night to no success, the question i have for you is that for a npn transistor doesnt the emitter base need to be forward biased and collector base reverse biased? so shouldn't you have a negative on the emitter not a positive output? and also how you used the diodes to get a voltage drop, it actually did the opposite, i had 9 volts out of LM7809 and about 11 on the base.

    i learnt all of this using electron flow not conventional flow and none of what you have drawn up makes sense in my head from what ive learnt, any chance you could explain your drawings?
     
  5. wayneh

    Expert

    Sep 9, 2010
    12,094
    3,033
    Then something is terribly wrong. Perhaps you have the pinout of the transistor wrong?

    Both circuits regulate by using an emitter-follower configuration. The emitter voltage rises until it is the base-emitter diode drop below the base voltage. Pretty clever, I might add.

    I wonder if the voltage could creep up - leakage from the collector - if there is no load at the emitter?
     
    Last edited: Oct 14, 2014
  6. #12

    Expert

    Nov 30, 2010
    16,261
    6,768
    Absolutely! But Jordan didn't say he wanted to measure this with no load. He said he wanted it to provide 3 to 5 amps. Under that condition, these should work.

    ps, I did the math about "typical" base current, Vbe, and DC gain, and found that 4 diodes should be as good as you can get in the 7809 design. Then, consider the range of gain can be as low as 20 on a 2N3055, and you will only need 2 diodes to get the output down to 6.2 volts. That's reality. You have to fit the circuit to the parts you have if you don't have all day to go buy stuff and design tight circuits.
     
    Last edited: Oct 14, 2014
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