Rectifiers in parallel

[Mike Watterson]

I have had similar problems with load sharing using 78xx voltage regulators in parallel. There is always one that runs hotter and eventually fails first.

That doesn't work. But there is a way to add external transistor(s) to an LM317. It is very sensitive to layout and like the higher power LM317 it can "sing" from audio to RF, depending on layout. Getting 20A on an LM317 + transistor circuit was challenging.

You can also add an external transistor to an 78xx, but the regulation is poor compared to the LM317 which has a feedback pin from a divider on the output instead of the 78xx earth/common.