Need 5V 5A SMPS modification

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bencyp

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Hi,

I have a laptop adapter that generates 18V 3.5A output. Attached is the circuit of the adapter. I want to modify the same for an output of 5V and 5A.

I have made the changes on the resistor (W1) 1K but I am able to increse the voltage, however, when I reduce it below 12V the SMPS starts ticking sound every second (approx).



Can I modify to get 5V output?

Regards,
Bency
 

Hi,
I dont believe, that you can do it if the transformer & L3 will be not changed too...
Than, the Optocoppler need instead the R18=3.9K surly other resistor too. The AZ431 needs minimum 2.5V, than in TLP521 the LED=>1.3V; you have ca. 1.2V on R18, calculate the same current value for it as yet from 18V...(I think-it cant be higher as 330 Ohm)
To end are the snubber and Z2 in (changing)play too...
K.
Check pls for 431 dimensionings Fig.5, 17 & 21.
 

I understand that AZ431 needs 2.5V which I can give by changing R16 and R17 and also by changing R18 I can get the optocoupler to triger at 5V.
The SA12A is a 500 Watts Transient Voltage suppressor which will not make much difference if I reduce the voltage to 5V.

So, all I have to do is reduce the number of Secondary turn and change the L3. Correct me if I am wrong?
 

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