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Adjustable AC voltage

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by fezder, May 14, 2012.

  1. fezder

    fezder Well-Known Member

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    what values you mean? R1 is 470ohm/1w
     
  2. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    That's probably too high of a value. The 2N3055 doesnt have enough gain for that. You can estimate the base current with Ib=19/R1.
    You'll also have to make sure it has the proper power rating.

    What about the other resistor,on the emitter, what it that value?
     
  3. fezder

    fezder Well-Known Member

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    welll that resitor on the emitter is what i meant for inductors load point, sorry i meant to use coil marking but used resistor :D
     
  4. dave

    Dave New Member

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  5. fezder

    fezder Well-Known Member

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    hey again, i did some changes to circuit, and load is only amp meter
    i did notice one thing: at first, current doesnt change at all, then it starts to change pretty quickly, is this because of 2.2 voltage drop caused by transitors?
    should i use this current adjustment, or what i hope, do you have better solution? :S
    http://i45.tinypic.com/bhgh01.png
     
  6. 4pyros

    4pyros Well-Known Member Most Helpful Member

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    From Post #94
     
  7. fezder

    fezder Well-Known Member

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    yes i know that now :D i dont intend using breadborad anymore to this project, but what is god way to apply adjustable current
    should i stick to this schematic? sorry alll this back-forth questioning :S
    http://i45.tinypic.com/zxmlud.gif
     
  8. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hello again,


    Get rid of the MOSFET, use a bipolar.
     
  9. leonardason

    leonardason New Member

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    Yup, my vote goes to a variac. I recently got one (a friend of mine was very generous and gave it to me ) and I love it! It's just a big variable transformer--that's all it is. You can find them on ebay for about $30-$70 USD (about 23€-55€). Of course, that'd be a very simple, low-current (maybe 5-amp) variac. It'll work for simple projects--might be worth looking into.
     
  10. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    Oh yeah variacs are nice. I had a big one long time ago. Now i just have a very small one.
     
  11. fezder

    fezder Well-Known Member

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    i would buy one if i could afford one :) and i should buy it abroad, haven't seen any available in Finland, only i have used is at school at therefore under use....
     
  12. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    Well they are a little expensive too so maybe not worth it unless you have to use it every day or something.
     
  13. fezder

    fezder Well-Known Member

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    Sorry i had lots of stuff going on, school and all, so i couldnt focus much on this project.... but, if you could help me with simple matter. its about this circuit you posted
    http://www.electro-tech-online.com/attachments/

    i know the basic idea behind this circuit, BUT, what purpose is for that potentiometer(?) in the ref voltage place? does that determine how much op amp will drive transitor to produce reguired voltage to inverting input via R1?
     
  14. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    Sets the current of the output.
     
  15. fezder

    fezder Well-Known Member

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    ok, i processed some with this project. now, the problem is thermal runaway of the transistor, if i got it right: more current->more heat->more current->more heat.....until transistor is overheated, or PSU's fuse will blow (unlikely?) i thinked about this problem, and i thought about more cooling (bigger heatsink, fan, or even thermal shut-off) but, i thought i should ask here too, so is there any workaround in this problem? i could add extra transitor in paraller with exicting one to inrease amperage handling, but this involves adding some cind of small resistance resistors in transitors emitters to balance current between transitors. but, what do you think for solution?
     
  16. fezder

    fezder Well-Known Member

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    no worries anymore, i got it stabilized, found circuits and other help form google :)
     

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