> I archive all data sheets I run across and I found this information > on both TI and Fairchild data sheets for the 78H05, LM340 and LM78XX > devices - it is usually under a heading called Application Hints and > for some reason Fairchild have removed these Hints from the sheets > you quote.
> In ALL cases the manufacturers caution that putting voltage to the > output when the input is not powered CAN DAMAGE THE CHIP. I have the datasheet PDF for the On Semiconductor version, and I have been unable to find anything of the sort in it. Whether On was sloppy when writing their documetnation or whether some manufacturer's devices are safe or whether I just missed something, I don't know. But, when dealing with a device of unknown provenance, it does seem clear you're better off not powering the output side if the input side has a low-impedance path to ground. (Powering the output with the input disconnected appears to be a completely different thing; I have trouble imagining a design that would be damaged by that.) /~\ The ASCII Mouse \ / Ribbon Campaign X Against HTML mo...@rodents-montreal.org / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B
