Linear stabilizer

Thread Starter

Ron Potashnik

Joined Dec 27, 2015
16
hello. i have questions about this linear stabilizer circuit.

1)what is the need of a capacitor and why dose he so important in this circuit?
2)why cant i charge the circuit more than 13v in a load test?
3)why R1 have to be big resistor(4.7k)? what is the purpose of the resistor R5?
tnx
1.png
 

Papabravo

Joined Feb 24, 2006
12,775
3) R1(4.7K) limits the current through the zener diode.

You don't specify the input voltage range or the output voltage range so the other questions are hard to answer.

IMHO, the 741 does not really like single supply operation and there should be a bypass cap on the supply pins.
 

anhnha

Joined Apr 19, 2012
880
1)what is the need of a capacitor and why dose he so important in this circuit?
The big output capacitor along with output resistance of LDO will be the dominant pole of the system. This makes it easier to compensate compared with one without output capacitor.
 

anhnha

Joined Apr 19, 2012
880
But this circuit is not a LDO type.
From this page, it is an enhancement of transistor regulator. I think it can be called a type of LDO. The only different I notice is that in LDO the BJT transistor is not a voltage buffer as above. So maybe no compensation is necessary for this.
 

Jony130

Joined Feb 17, 2009
5,127
This circuit with NPN transistor (series pass regulator) is "very far away" from low dropout regulator (with PNP ) and usually needs no output capacitor for stability.
 

WBahn

Joined Mar 31, 2012
25,122
Since this IS Homework Help -- how about hearing YOUR thoughts on what might be the answers to the rest of your questions?
 
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