how connect transistor tip142 to pic

Discussion in 'Homework Help' started by hertz.12, Jan 24, 2016.

  1. hertz.12

    Thread Starter Member

    Apr 25, 2015
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    0
    hi
    i m trying to interface tip142 and tip 122 to pic 16f628 to drive 10A load....the problem is i don't get 10A out..only about 7A out and the tip 142 get hot after 5minutes ..not too hot so it is ok but i need 10A..what is wrong?


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  2. WBahn

    Moderator

    Mar 31, 2012
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    You are saying that your load is 1 Ω and that it is powered from 9 V. How do you expect to get 10 A into it in the first place?

    Look at the data sheet for the TIP-142 and you will see that the Vce saturation voltage at 10 A (and Ib = 40 mA) is spec'ed to be less that 3 V. So even if you only got 6 A you would have nothing to complain about.
     
  3. Papabravo

    Expert

    Feb 24, 2006
    10,138
    1,786
    Did you know that both the TIP122 and the TIP142 are Darlington transistors? You do know what that means -- Right?
     
  4. hertz.12

    Thread Starter Member

    Apr 25, 2015
    36
    0
    yes i want 9A not 10A.....

    why i can't get 9A from tip141? now i get 6A no more...what is the wrong?
     
  5. hertz.12

    Thread Starter Member

    Apr 25, 2015
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    yes i think i know both Darlington transistor
     
  6. WBahn

    Moderator

    Mar 31, 2012
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    You start with 9 V. You have a transistor that saturates with as much as 3 V from collector to emitter. That leaves 6 V across your load, which is 1 Ω. How much current will flow through a 1 Ω load that has 6 V across it?
     
  7. WBahn

    Moderator

    Mar 31, 2012
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    So why are you using two Darlingtons in a Darlington configuration? The TIP-142 has a beta of ~500, meaning that to support 10 A you would only need 20 mA of base current. What can the PIC provide?
     
  8. hertz.12

    Thread Starter Member

    Apr 25, 2015
    36
    0
    yes i think pic can provide 20-25ma but i prefer not to reach maximum pic output...i will use npn2222 instead of tip122

    i thought that tip 141 can drive 10A load...there any way i can drive 9A with tip141?
    thanks
     
  9. WBahn

    Moderator

    Mar 31, 2012
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    It can. Make your load 0.5 Ω and you will see. It's not the transistor that is limiting your current.
     
  10. Bordodynov

    Active Member

    May 20, 2015
    637
    188
    See

    Ex1.png
     
    absf likes this.
  11. Bordodynov

    Active Member

    May 20, 2015
    637
    188
    From my pictures easily calculate the power transistor.
    7.606A*1.394V=10.6W !!! We need a big heatsink!

    8.933A*66.86mV=0.597W You do not need a heat sink.
     
  12. hertz.12

    Thread Starter Member

    Apr 25, 2015
    36
    0
    thank you all....good info
     
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