Current Amplification

Discussion in 'The Projects Forum' started by Alienite, Oct 15, 2016.

  1. Alienite

    Thread Starter New Member

    Oct 15, 2016
    3
    0
    Hello, I need to amplify a low current (30mA) voltage signal to a higher current without changing the voltage. The device requires about 700mA for optimum performance. The input voltage is 5v.

    I understand that I may use some NPN transistor but I've no idea which one. Also I've read that transistor is an active device, so i'll need an additional power source for it?

    Any help you can provide is appreciated.
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,016
    3,235
    A BJT NPN emitter follower circuit should work for you provided you can tolerate about a 0.7V drop from the input to the output voltage (in other words, with a 5V input, the output will be about 4.3V, albeit at the high current you want).
    Yes, you will need a power supply of a least 5VDC.

    If you can't tolerate that much drop, then you will need a more elaborate circuit, such as an NPN coupled to a PNP.

    Is this just for a switching action output, or does the input vary in voltage between 0V to 5V and you want the output to follow?
     
  3. Alienite

    Thread Starter New Member

    Oct 15, 2016
    3
    0
    At this stage I dont think 0.7V drop will affect the performance. And the input will remain constant all the time.
    I've attached a circuit, kindly verify if it's correct.
    Also, u mentioned a BJT NPN emitter follower; kindly tell the name of this device that I can tell to the shop guy.
     
  4. Alienite

    Thread Starter New Member

    Oct 15, 2016
    3
    0
    I've done some data search and I've learnt that I need a transistor with peak current more than the value that my device needs, that is more than 700mA, and with a gain high enough for the input current to cross 700mA. And then i'll have to add a resistor with the base to compensate for the additional current that the transistor will produce. The thing is, I'm all confused with choosing the right component and the calculation. Can u help me understand this part?
    Thanks for your time!
     
  5. crutschow

    Expert

    Mar 14, 2008
    13,016
    3,235
    If you can put the load on the high-side, as you show in your diagram, than an N-MOSFET would be better, since a BJT should have at least 70mA base current for 700mA collector current.
    That would deliver nearly the full 5V to the load.
    Where do you purchase electronic parts so I can suggest a device to use.
     
  6. Colin55

    Member

    Aug 27, 2015
    191
    19
    We need a lot more information.
    Supply the input waveform, the acceptable distortion, the actual current required by the load, the type of load, before we can advise you.
     
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