How to amplify an AC signal

Discussion in 'The Projects Forum' started by simeonz11, Aug 16, 2009.

  1. simeonz11

    Thread Starter Active Member

    Apr 29, 2008
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    I wish to amplify a small AC signal to a big power signal .

    I'm using this op amp made for hv operations , it says its made for hv . itr has a maximum current of 50mA .

    http://focus.ti.com/docs/prod/folders/print/opa445.html

    This is my circuit , the goal here is to power a transformer with this AC signal , using only batteries . I know emitter-follower , thats easy on its own , but This is an AC follower emitter so I just cant figure it out by myself now .

    I usually try to figure things out on my own , but for this I am just stuck . I dont wanna spent any $ on testing and I dont have a sim .

    I just need a good schematic to amplify this signal , the "whats next" .

    I think alot of people would also like to know this .
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    The circuit does not show.
    It is linked to a local disk.(your C drive)

    Greetings,
    Bertus
     
  3. simeonz11

    Thread Starter Active Member

    Apr 29, 2008
    98
    0
    OOps , fixed .
     
  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    How much current do you need?
    The OPA445 can deliver 15 mA.
    There are others mentioned on the page:

    See Also


    • OPA452 - 80V supply with 50mA continuous output instead of 90V, 15mA.
    • OPA551 - 60V supply with 200mA continuous output instead of 90V, 15mA
    Greetings,
    Bertus
     
  5. simeonz11

    Thread Starter Active Member

    Apr 29, 2008
    98
    0
    Thx Bertus .

    Well I am currently using a tl082 for my testing pusposes , it is a fet input .

    Whats the difference with a fet input and another I dont know , I know this one and like it .

    Do I have to add or change anything with the other ? I'll use the 200 or 50 if its the same exact thing .

    I purchased a high dollar high current lm675 from DIGIKEY buy that piece of crap messed up my input signal , can you imagine that lol ? I tought it was the other way around , the inpout signal has an effect on the output, not the other away around !!!!!!!! Its just a load of trouble to get it goin right .

    I was gonna need a transistor stage anyways .

    So Now i'm using a high voltage lower current less $ with an emitter followr stage . at leats I'm trying to
     
  6. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    What frequency do you want to amplify?
    How many gain do you need?
    The OPA551 and OPA 552 will work upto ± 30 Volts.

    Greetings,
    Bertus
     
  7. simeonz11

    Thread Starter Active Member

    Apr 29, 2008
    98
    0
    anywhere from 50 to 15000 hz

    I dont know how much current , enough to make my emitter follower where I= V/Rload

    just that really , I want to mimic my wave and provide current based on whatever load I have ...

    Nothing more than 4-5 amps .
     
  8. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    What will be the load?
    In what resistance range will the load be?

    It sounds like an audio amplifier to me.

    Greetings,
    Bertus
     
  9. simeonz11

    Thread Starter Active Member

    Apr 29, 2008
    98
    0
    Hi bertus

    Nothing below 20 ohms , not too much power .

    Its for a "special" science project .
     
    Last edited: Aug 16, 2009
  10. bertus

    Administrator

    Apr 5, 2008
    15,647
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    Hello,

    When you say 5 A and 20 Ohms the power will be ( P = I X I X R ) = 5 X 5 X 20 = 500 Watts.
    For 5 A in 20 Ohms you will also need ( U = I X R ) = 5 X 20 = 100 Volts to get it.
    This is quite a power.
    If the resistance is even higher the power will rise too.

    Greetings,
    Bertus
     
  11. simeonz11

    Thread Starter Active Member

    Apr 29, 2008
    98
    0
    Hi Bertus.

    That would be in the worst case scenario .

    The resistance will be higher than 20 ohms .

    I will never reach anything close to 500 watts load . Maybe not even 100 .

    That would be defeating the purpose of my special project .

    I am not worried about maximums here .
     
  12. bertus

    Administrator

    Apr 5, 2008
    15,647
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    Hello,

    What will be the maximum load resistance?
    You say it is higher than 20 Ohms, but not how high.
    I think the current will not be higher than about 2 A.

    Take a look at the attached PDF about voltage to current converters.

    Greetings,
    Bertus
     
  13. simeonz11

    Thread Starter Active Member

    Apr 29, 2008
    98
    0
    Hi bertus,

    Like I said , it all depends on the resistance of whats on my secondary side , it all depends .

    I dont have any solid numbers but the goal here is to go for low amps .

    Thx for that pdf , that howlad bidirectionnal current source looks good for my application , do you think so ??
     
  14. simeonz11

    Thread Starter Active Member

    Apr 29, 2008
    98
    0
    Ok I have identified 2 possible working circuit .

    I need your opinion .

    My goal is to run a transformer remember and immitate the wall plug only higher frequency.

    I wanna know whats the difference between these 2 , what dooes the "current sense" do anyways ?

    There is not much info on this bidirectionnal current sense .

    is this needed at all , wich one of these would be best for my application , I have no idea about that Rsense thing

    Also , wouldnt the transistors need diodes before them to protect them from reverse voltage ??

    Theres gonna need a base resistor also ...
     
    Last edited: Aug 16, 2009
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