Current Amplification

Discussion in 'The Projects Forum' started by rahdirs, May 22, 2013.

  1. rahdirs

    Thread Starter New Member

    May 22, 2013
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    Hi ppl,

    At the output of my circuit i have an opamp that gives out 12V & 10mA,but the next stage of my circuit needs 12V & 5A,how do i provide this current amplification.
    I tried using buffer circuit,but it showed no improvement,
    The buffer was implemented using IC 741 as voltage follower.

    Regards,
    rahdirs

     
    Last edited: May 22, 2013
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,974
    744
    You need to provide us with your circuit,

    also the supply that your using needs to be able to give out at least 6Amps, and use power transistors to buffer the output.
     
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,006
    3,762
    Going from 10ma to 5a requires 500 gain. Standard op amps don't generally drive more than 10 to 30 mA.

    If this is an on/off comparator circuit (square wave, for example), then a MOSFET transistor will work. It is essentially a fast on/off switch.

    If you need a linear response in your 0 to 12 volts range, then a bipolar transistor is best. However, we will need some more detail on wave shape and output swing - how close to each supply rail are you hoping for, ...
     
  4. MrChips

    Moderator

    Oct 2, 2009
    12,431
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    Show us your circuit.
    You don't amplify the current with an opamp alone. The 5A has to come from the power supply via a low impedance device such as a BJT or power FET.
     
  5. rahdirs

    Thread Starter New Member

    May 22, 2013
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    The 12.54V that you see in my circuit is output of circuit(fig.2 circuit) that gives 12V from 220V AC Supply.

    I shouldn't use current from power supply in my circuit(fig.1)
     
  6. MrChips

    Moderator

    Oct 2, 2009
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    You cannot get 5A from your circuit.
     
  7. rahdirs

    Thread Starter New Member

    May 22, 2013
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    But my circuit needs to drive an inverter that converts it back to 220V,so is there no way to get it 5A(or even 1A).

    I agree that op amps can provide at max 30mA o/p current,but is there no other way like using line drivers the way they use it for DAC's.

    Ok, I will explain what i am trying to do in my circuit.
    I have a varying voltage source that varies between 0V & 12V providing 7A current.I have to make it to a constant 12V so that i can up convert it to 220V AC and use it power devices(storing my ckt 12V o/p in a battery bank & then an inverter to produce 220V AC).

    So,what i did was down convert grid voltage 220V Ac to 12V DC.I then subtract the two voltages(grid voltage - varying voltage),then i added the gradient between the two voltages to the varying voltage so that i get a constant 12V o/p,now i up convert this 12V o/p to 220V AC.

    The reason i can't use grid to bring the o/p current to 5A is i want to use varying voltage source to power my battery bank.
     
    Last edited: May 22, 2013
  8. MrChips

    Moderator

    Oct 2, 2009
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    So you are trying to build a converter to go from 12VDC to 220VAC.
    That is not the way to do it.
     
  9. rahdirs

    Thread Starter New Member

    May 22, 2013
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    Yes, the 12V dc is actually coming from a solar panel(hence varying voltage-it gives different voltage at different time of day).

    So,are you saying that the way i am regulating the panel volatge to 12V is wrong or the method of converting 12V to 220V is wrong.

    I can change my problem statement a bit to, the output 12V of my circuit can charge a battery bank which can be connected to inverter to change it to 220V AC,but i still need current of 5-7A to charge battery.

    Can u suggest/give a hint of doing this in any other way.
     
  10. MrChips

    Moderator

    Oct 2, 2009
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    I always suggest to AAC posters to state up front in the first post what you are trying to do. Without this we are all discussing a problem and offering possible solutions with no relevance to the actual problem.

    The circuits you have shown have no relevance to the problem.

    You have two separate problems:

    1) How to charge a bank of storage batteries from PV solar panels.

    2) How to convert the voltage from the battery to 220VAC.

    This is a systems design engineering project and has little to do with circuit design.

    The first thing you have to do talk about is power. How much power do you hope to generate from your battery bank.? Next you have to match the power of the PV solar panels, storage batteries with your power requirements. You have to state your location, latitude and longitude, and solar energy availability.

    After you have done all of that, you go out and buy the components.
     
  11. rahdirs

    Thread Starter New Member

    May 22, 2013
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    I agree with u if i just have to use a solar panel,u match power ratings of solar panel & battery bank & use a charge controller and just buy out components.

    I'm using a battery bank of 12V rating.
    But,I have to increase the duration of operation of solar panel by combining it with grid voltage so that when the solar panel voltage drops,the grids helps it by bringing its voltage up to 12V
    .

    Sorry for my hand writing in image,but i think that i need to implement the circuit of functional diagram of attached image before just buying components.

    I simulated the below schematic in Multisim using Summer & Subtractor Control function & inverter worked fine,so i think i should nw just try to implement subtractor & Summer with components in place of the Summer & Subtractor Control function implemented in Multisim

    My project is explained in attached 2 images.

    Thanks for the help.
     
    Last edited: May 23, 2013
  12. rahdirs

    Thread Starter New Member

    May 22, 2013
    28
    0
    I changed the circuit and got a bit of current amplification by using Class AB power amplifiers,but i still get a current of 1A,is there a way to make the current go upto 10A.

    I am currently getting a current gain of 60,but is there a way to get a current gain of 500. I tried using Darlington configuration in class AB amp but it didn't work.

    The circuit after the marked area in schematic is a simple 12V DC to 120V AC inverter.
     
  13. Kishore kumar.K.P

    New Member

    May 28, 2013
    2
    0
    Hi,
    I have one question,
    Is it possible to amplify the current in the O/P of 12.5VDC?
    I will be waiting for your reply.
    Thank you..
     
  14. rahdirs

    Thread Starter New Member

    May 22, 2013
    28
    0
    Your question isn't clear,as to where is that 12.5V DC is ?

    But if your asking in a general scenario, you can.


    • Consider a buffer with an Opamp using voltage follower.It reduces output impedance and hence increase in current.

    • You can also see AB class power amps.They provide current amplification.
      Or even a simple BJT
     
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