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Transistor question

Discussion in 'Electronic Basics' started by ngdbud, Dec 11, 2005.

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  1. ngdbud

    ngdbud Guest

  2. Lord Garth

    Lord Garth Guest

    The schematic is correct...

    A positive voltage on the base will cause current to flow from the base to
    the emitter
    and into ground. When this happens, a large current will also flow from the
    12 volt
    supply through the coil and transistor and into ground.

    Think about the circuit using conventional current, from + to - rather than
    electron
    flow.

    PS. heat sink that 2N3055 very well!
     
  3. Pooh Bear

    Pooh Bear Guest

    Yes.

    The collector is indeed positive wrt the emitter. See that " + " before the 12V ?

    It would be conventional practice to say that the emitter is connected to ground and the positive suply
    is connected to the collector load btw.

    Graham
     
  4. The little arrow in the symbol always points in the direction of
    *conventional current flow* which is (historically) from positive to
    negative. This is the opposite of electron flow, which is what we are
    *really* concerned with. So the arrows in these symbols basically
    point the 'wrong' way.
     
  5. ngdbud

    ngdbud Guest

    Thnks, I have a small peltier cooler and a heat sink should use both?

    P.S. the peltier is just a small 1.5v one, should i use a voltage
    divider or is there some better way to divide the voltage by eight?
     
  6. Since a peltier is run on current, a series resistor is the simplest
    way to regulate the current. But you will be wasting 7/8ths of the
    power that way. A more efficient way (but a more complicated one)
    would be to use a buck switching regulator, that converts power to
    power. So, for example 8 volts @ .1 amp (.8 watt) in, would become
    1.5 volts @ 5.333 amps out, minus switch and inductor losses. Losses
    might be 10 to 20% of the output power. There are some integrated
    circuits that do most of the work for this sort of thing. You just
    add and inductor, a couple capacitors, and, perhaps a Schottky diode.

    See simple switchers under switching regulators at:
    http://www.national.com/catalog/0,4567,74,00.html

    Here is a tutorial on buck switching regulators:
    http://www.national.com/appinfo/power/files/f5.pdf
     
  7. Lacy

    Lacy Guest


    As an aside from what Paul.has mentioned, You could also say that the arrow
    always points to the N-material in semiconductors. This is especially
    helpful when dealing with JFET or MOSFET devices when determining channel
    type.This the way I learned it anyway. Thought this might be helpful to
    know.
     
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