simpliest isolated DC/DC converter ??

[settra]

hello forum. i want to create a simple isolated DC/DC power supply. the propouse will be to take Vin 10 - 16v (car battery), and make it fixed 12v . max ampere could be something around 3A. the thing, is, that all the schemantics i have found, are a bit complicated, or do not explain themselves....

so, could someone, give me a simple schematic, or help me understand, how the optical feedback works, and how it controls the oscillators freq?? thanks!!

 

[settra]

i could aslo Buy one, if some one , knew a place that ships to greece...

 

[ronv]

Since it is a dc to dc converter is there some reason you need the isolation?

 

[settra]

yiap/ in my car i have a carpc. my lcd has a ground loop with the computer, wich i cannot find in any way 2 years now... the only way to break the ground loop would be to change the LCD power supply with an isolated one...

 

[Maged]

the problem with dc-dc converter will be the transformer and its winding, if you have access to ferrite cores or transformers, I can help, but if you can not and have to use classic iron transformer, it will be bulky but yet possible. In any case you will have to wind your transformer.
I searched but for no apparent reason they do not provide 12vdc in and out, only 24 to 12, but you can find converter or inverter for up and another for down..
the optical feedback is simple, the output voltage is applied to a resistor in series with an IR emitting diode, its light will increase with output increase, this light falls of a photo transistor so its conductivity increases with IR from the diode, this change in conductivity causes the control IC to vary the output pulse width.
Also most of the SMPS vary pulse width rather than frequency.

 

[settra]

can you recomend any chip, for controller?? and why cant i use a transformer, of the shelf??

 

[settra]

BY THE WAY, i have found those:

https://gr.mouser.com/ProductDetail...=sGAEpiMZZMtwaiKVUtQsNTnembC/VxYWnqz2rXBmxoY=

https://gr.mouser.com/ProductDetail...=sGAEpiMZZMtwaiKVUtQsNU4R2kSbYqvX9mjKzUqTYtA=

how do they seem to you??

 

[Maged]

SG3525 = LM3525 = UC3525, the data sheet has some schematics too, I did not say you cant use off the shelf transformer, but you have to find it first!!
The transformer you need will be something like 8-0-8 for input and 12-0-12 for output or close to it

The two "mouser" units look to me great

 

[dr pepper]

You can do this with a high freq ferrite transformer and the usual, or you could use a standard mains transformer with 2 12v o/p's, that is 0-12 and 0-12, not 12-0-12, if you drive one of the 12v o/p's from 12v at around 100 - 200hz you'll get a 120/230v and 12v ac isolated supply, rectifying the 12v gets you a dc supply slightly higher than 12v depeding on the load.