2- questions about reglation and transformer

Discussion in 'Homework Help' started by braddy, Oct 30, 2007.

  1. braddy

    Thread Starter Well-Known Member

    Dec 29, 2004
    83
    0
    Hi,
    I have two question about transformer and regulator:

    1- When one refers to “isolation” with respect to a transformer, what does it mean?

    It related to the fact that the transformer blocks DC component of the signal?

    2-
    this question is related to the electronic regulator 7812.
    If the input line voltage decreases beyond a certain point the series regulator will stop regulating. Why?
    I have attached the circuit related to it.

    Thank you
     
  2. recca02

    Senior Member

    Apr 2, 2007
    1,211
    0
    about the transformer:
    isolation means electrically separating the primary side and secondary side so that there is no direct connection between the two circuits. the primary and secondary are electrically isolated and magnetically linked.
     
  3. cumesoftware

    Senior Member

    Apr 27, 2007
    1,330
    10
    Regulators need the input voltage to be at least 2.5V above the output voltage. Once the voltage is below that threshold, the series pass transistor built in won't be properly driven by the operational amplifier (called error amplifier in the context of a regulator). The amplifier compares the divided output voltage (divided by a voltage divider) with a voltage reference. Below a certain voltage the voltage reference won't have enough current to be stabilized (typically, it is a zener fed by a current mirror). So the amplifier won't drive the series pass transistor properly and the regulator will stop regulating.
     
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