2- questions about reglation and transformer

Thread Starter

braddy

Joined Dec 29, 2004
83
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
 

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recca02

Joined Apr 2, 2007
1,214
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.
 

bloguetronica

Joined Apr 27, 2007
1,372
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
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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