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johnyp 6th July 2006 01:57 PM

Simple 12v Smps
Hello to all.
I need to make an smps that will powered from a car's 12v battery.
The secondary must have +/- 12v & +/- 5v about 1A each output.
From what i read in this forum i assume that primary must have the same windings with the 12v secondary and almost double from 5v secondary.
But how many must be the first winding.
I want to use sg3525 because i have many of those.
My purpose is to power up a dvd player for my car since i have only an in-dash lcd with tv and scart input.

Maybe i can use the dvd player's original power supply by changing the etd type transformer.

Pls advise

Thank you in advance

luka 6th July 2006 05:55 PM

You need to make regulated one for your LCD,therefor I would wind 20% or more for 12 and 5v outputs.SG will be perfect for the job.

johnyp 7th July 2006 07:51 AM

My dvd player unit doesn't have an lcd .
It is a slim small unit with only the basics.
I want make another transformer for it's original smps.
I mean maybe i can use the original smps with another transformer set to work to 12v instead 220v.

Thank you

johnyp 7th July 2006 07:51 AM

By the way my players original smps uses TEA1523 chipset.
The transformer has 2 windings of primary coil. One for the oscillation and one for powering the TEA chip.
All i wabt to know is how to make another transformer.
I am thinking that if i make one with for example 10 turns primary it will draw too much current from my car.

The dvd players car supply secondary is only maximum 1A.

Pls suggest me something.

I am willing to make a new smps but i am afraid that i will fail in the transformer.

Thank you in advance

luka 7th July 2006 08:56 AM

you make new will draw only so much current as it needs to operate and to supply what ever you want.In your case it will draw <3A from car battery

johnyp 7th July 2006 10:03 AM

How many turns must have to primary coil and how many to secondary?

Thank you.

luka 7th July 2006 10:43 AM

10 to 20, but be careful for current rating

johnyp 7th July 2006 11:11 AM

So i will use 20 turns for primary.
Any simple circuit for push pull without chip.

johnyp 7th July 2006 01:08 PM

I attached a pcb i made using sg3525. I took it from

I plan to use small fets cause i want only 3A output.

What do you think?

Thank you

johnyp 7th July 2006 01:08 PM

2 Attachment(s)
Sorry here it is.

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