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Query on power supply using LM317

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t_malavika

New Member
Hi all,

I need some help in figuring out the function of some components in an adjustable power supply using LM317.

The previous stage in the shown circuit is a bridge rectifier

The PCB has 2 transistors 2N4401 coonected as shown and with an LED.
what is the purpose of the transistors and LED.
I understoof the circuit of the LM317 ok. But why the zener there? it is a ZN423.

Also i'm not able to recognise the component drawn as a box between the capacitors c1 and c2. It has just "5%" printed on it. It looks the size of a half watt resistor and but feels ceramic.also why c1 and c2. are they both as filters here? why is + of C2 earthed instead of the supply negative itself?

Could someone please help out.

Thanks a lot
 

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panic mode

Well-Known Member
That's must be the ugliest schematic i've seen so far. :shock:
Part that is really disturbing is lack of connection points and
the drafter doesn't even know how to draw a straight line.
Anyway, the schematic doesn't show everything. Important part
is not shown and it is before rectifier (center tap from the transformer
is probably not connected to ground but to emitters of the transistors).
The ZN423 is not a zener diode it's voltage reference.
If you want to use 12V zener, it is not connected properly (ends
are swapped around).
T2, D2 and R4 are used to shut the output down when
emiter is biased negative in reference to ground (foldback circuit).
At the same time first transistor would turn on the
LED (probably red) to indicate overcurrent condition.
 

mozikluv

New Member
regulated supply

:D hi,

my suggestion is redraw your circuit, show all the proper connection so we may give you the proper response. anyway the response of panic mode will give you a start on understanding your circuit. :D
 
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