lm317t power supply, need feedback

[little_carlos]

hi, im about to do this design for a power supply that im about to do, the lm317t that i bought was faulty so il get another one

I want it to power my little electronics projects, but im making it 30v- 3 amps so if someday i need it, i could use it
ive already bought the components so please tell me how accurate will it work, i understand that the lm317t is for controlling the 2n3055, im using this power transistor so the lm317 dont melt down and burn up all the chasis

[mariush]

You already asked here, stick to one thread: https://www.eevblog.com/forum/beginners/lm317t-power-supply-question/msg425831/#msg425831

Did you even check the datasheets I linked to, to see the example circuits shown inside the datasheets?  Did you read the advices other people told you, or you're just stuck on that picture?

[digsys]

I'd seriously consider it's larger brother - the LM338K, which is the 5A version !! The BIG problem with pass transistors is that
you lose thermal shutdown in case of a short !! (It's built into the Regulator only). That circuit does work though with limitations

[little_carlos]

i dont find the lm338 anywhere 

[mariush]

You can also look for LD1084 , LM1084 , or anything with 1084 in the name .. these can do 5A with good heatsink.   LD1085, LM1085 , *1085 can do 3A.

No matter what you pick - and I already explained it to you - linear regulators dissipate the difference between input voltage and output voltage as heat ... number of watts wasted is (Vin- Vout)  x Current ...

Stop trying to use use a simple transformer that will give you 30v dc at the input and use a transformer with two secondary windings - use just one winding when you need lower voltages, connect both windings when you want higher voltage. 

For example get a 24v AC transformer with center tap or two separate secondary windings .. when you connect just one winding to bridge rectifier, you get 15v DC, when you connect both windings in series, you get 30v DC. So when you want to have 1.25v - 12v you use just the first winding, when you want more you connect both windings in series.