how to choose transformer for power supply design

[kupper]

Hello,
I have a question on transformer selection for liner voltage regulator type powersupply circuit.

What is VA rating for a transformer? Is it true that if the VA is too big the transformer will heat up and waste alot of energy?

I setting up a ps circuit using 7805, 5V output about 200mA~300mA load.
Transformer input is 230V pri, around 13 or 18V on the secondary without load.

Appreciate any help and comments.

Regards,
Nev

 

[IanP]

Choose a transformer with secondary rating as follow: voltage ≈8-10V ac @ 500mA.
Bigger transformer, if physical size is not an issue, wouldn't heart, and it will not overheat because you don't draw rated current; it is opposite way around - if you select transformer with to small VA rating it will overheat.
Also to help you to select transformer-rectifier configuration, attached you will find "rectifier relationships" ..
Regards,
IanP

 

[kupper]

Thanks for the pointer IanP, Will look into it