No input voltage to the LM317 regulator?

[khouly]

about LM317

i saw a circuit using the regulator LM317
but the strange thing about it
i saw that when there is NO input voltage to the regulator , and i inserted a voltage on the output node , i found that the input of the regulator have a voltage and not isolated is this normal issue or not

and is this condition will defect the LM317

khouly

 

[IanP]

Re: about LM317

You will not damage the LM317 by connecting a voltage to its output, and this voltage will penetrate to the input pin (normal behaviour) ..
In some circumstances it is wise to connect a protective diode between output (anode) and input (cathode), and this diode will protect LM317 from rapid discharge from output to input pin in case input pin is shorten to 0V ( for example, big cap connected between input pin and 0V) ..

Regards,
IanP