[SOLVED] A simple current question

[thebadtall]

Hello I have a question.

If i have a 12v transformer 500mA , and use a lm317 regulator, is it possible to provide 1A to the load at 5V ?

thank you

 

[DIGITRONIC]

Yes it is possible

Input watt=12*0.5=6
Output watt=5*1=5

Output watt < Input

So, it is possible.

Thanks

 

[rfredel]

Hello thebadtall and DIGITRONIC,

NO, it's not possible.

DIGITRONIC, your calculation is correct, but the transformer will be going hot, because the wire resistance of the 12V winding is too high. The diameter of the wire is too small.

The 12V winding must deliver 1A because you take it at the output. You have a lost of P = (12V - 5V) * 1A = 7W at the IC.

Regards

Rainer

 

[BradtheRad]

You can just barely get 5V at 1A, by using a twin interleaved buck converter, with a supply input of 12V at 0.5A average.

However a resistive drop method (LM317), cannot give you greater current than is available from the supply.

 

[thebadtall]

thank you i got my answer!

 

[DIGITRONIC]

Sorry, I have not mentioned the current losses.

Thanks