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Discussion in 'General Electronics Chat' started by Nirvana, Apr 21, 2005.

  1. Nirvana

    Thread Starter Well-Known Member

    Jan 18, 2005
    Can anyone please tell me very very simply how a transistor works, ive been told that current goes this way and that was and leaves by this way etc etc.
    aaagggrrrhhh please help giving examples
  2. nanobyte

    AAC Fanatic!

    May 26, 2004
    A transistor is like a variable resistor. The way it works is a smaller current (the base current) is used to activate a larger current(the collector-emitter current). On this site under Volume III go to Bipolar Junction Transistors and then to the introduction section. They have an excellent easy to read explanation of transistors.
  3. pebe

    AAC Fanatic!

    Oct 11, 2004
    Hi nirvana. A bit off topic. But this is the second time today you have repeated the same request within 30minutes.

    Not everyone is signed on at any one time waiting to give instant replies to your questions. And in some cases, research is necessary before a reply can be given. So you really ought to wait a couple of days before repeating a request.
  4. Brandon

    Senior Member

    Dec 14, 2004
    A transistor is a current controlled valve in the most simple terms. Transistors has a specification calls Beta which relates the magnification of your control current to the output current. I.e., if you have a 1ma control current going into the transistor, and the transistor has a beta of 100, you have the potential to get 100mA out of the transistor.

    The controlling current for the transistor is supplied via the base. Now, the control current does not have to be positive flow, it can also be negative flow and there is a transistor for each condition. Your Typical NPN transsitor is activated with a positive current flow (postitive voltage) and the PNP is activated with a negative current (negative voltage).

    NPN design takes a positive voltage at the base, a positive at the collector. Current enters the base, beta * the current at the base usually enters the collector and the combination of the 2 leaves via the emitter. A PNP is reversed. A low voltage is put on the base, current leaves the base, beta*current leaves the collector and the combination of the 2 enter the emitter.

    They are used greatly as switches as well as small signal amplifies. Typical little sensors only give out tiny voltages or currents and a single transistor circuit can bring this up well into a usable range.