LM317 question

[polioli]

Hi , new to circuits and I'm making a voltage regulator using an LM317 . The circuits have diodes to take any excess voltage at the output away from the LM317 . My question is why can't you just put one diode at the output to allow current to flow out but not back?

 

[BobK]

You could, but you would lose regulation since the diode will have a different voltage drop at different currents. The diode backwards from Vout to Vin is there to protect from capacitors on the output side feeding a voltage back into the output pin of the LM317 when the power is shut off. It is not necessary in most cases.

Bob

 

[OLIVE2222]

Also the diode bridge output is reversed and D6, being shorted, is useless.

Olivier

 

[polioli]

LM317

Thanks for replies , I understand.

 

[davenn]

here's a corrected and improved circuit diag

cheers
Dave