op amp vs transistor

Discussion in 'General Electronics Chat' started by bradstormer, Nov 8, 2010.

  1. bradstormer

    Thread Starter Member

    Aug 6, 2010
    hi all,
    i am building a circuit where a sensor signal needs to be amplified.
    i am wondering weather to use a common emmiter circuit or a op amp feedback circuit?:confused:
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    Not nearly enough information to go on. In general, though, op amps are much easier to use, but that depends on the application.

    Tell us about the sensor output in detail.
  3. bradstormer

    Thread Starter Member

    Aug 6, 2010
    it is a dc motor used in reverse, the spindal rotates and generates a voltage
  4. SgtWookie


    Jul 17, 2007
    If you use an NPN as an emitter follower, you won't see an output until your motor's output exceeds ~0.6v. If you use a PNP as an emitter follower, your output will also be offset by ~0.6v.

    If you use a rail-to rail (or at least one that can sense down to the negative rail, or a bipolar supply with a standard opamp) you will have a minimal offset voltage; ~1mV-5mV for older opamps, and very low offset for newer opamps - and you can easily "program" the gain desired by using a couple of resistors.