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Discrete Current Boost/Pulse circuit

Discussion in 'Electronic Design' started by Neil, Sep 25, 2007.

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  1. Neil

    Neil Guest


    I'm seeking help to design a discrete BJT current boost circuit which
    can source a 600ma pulse for a duration of 200ms.

    Any help would be great...

  2. Tim Williams

    Tim Williams Guest

    Over what voltage range? Is current only forward?

  3. Rich Grise

    Rich Grise Guest

    At least this year, they're getting started on their class projects
    at the _beginning_ of the term, rather than waiting 'til the last
    minute. ;-)

  4. At what tyre pressure?

  5. Neil

    Neil Guest

    It's not a university electronics engineering project, or any post
    secondary electronics course related material either.
    I'm on my own on this one. OK.

  6. Neil

    Neil Guest

    Over what voltage range? Is current only forward?


    Tim, Well that would be between 10 to 12 volts.
    Current forward only. Yep

  7. Neil

    Neil Guest

    Martin, Pressure?..this is a electronics related question, it's a 600
    milliamp pulse at 200 milliseconds.
  8. Winfield

    Winfield Guest

    Why do you ask for a "current boost", as opposed to
    a current source, or mirror, etc. Do you possibly
    mean a current amplifier, getting say 6mA IN, and
    delivering 100x more or 600mA OUT.

    What do you mean by the phrase, current boost?
  9. Tim Williams

    Tim Williams Guest

    Then something like this will suffice.
    /---o Current sink
    R1 1k (1.2V) |/
    Logic in o---/\/\----+-----+---------|
    | | |\
    R2 | _V_ v
    1k > | 2 x | (0.6V)
    | | >
    | | |
    _|_ GND

    R3 = 0.6 / Iout.

    Or reverse the transistor and diodes for PNP (change GND to +V).

    A transistor like TIP29 should suffice. Actually, a darlington (TIP120,
    etc.) might not be a bad idea, in which case you will need three 1N914's in
    series. The transistor will need a small heatsink, as you will be
    dissipating about 12V * 0.6A = 5W.

    Rise and fall time will be under a microsecond. If you need faster, put a
    470pF capacitor across R1 and use a faster transistor.

    If you need more accuracy, you can use more base voltage (i.e., more diodes
    in series, or use a reverse-biased zener instead), in which case R3 needs
    to change accordingly.
    You can also cascode it:

    o Iout
    2.2k (3.3V) |/
    +V o---/\/\---+-----|
    _|_/ |\
    3.3V //_\ v (2.7V)
    Zener | |
    _|_ GND o To above collector

    Again, flip if you need a source.

  10. John Fields

    John Fields Guest

    1. When you say "current forward" do you mean that you want the
    circuit to send current to the load (source current) or do you mean
    that you want current to come from the load into the circuit (sink

    2. How often do you want this current pulse to appear?

    3. Is the amount of current to be determined by the load resistance
    or by the circuit?
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