Latch up with 7800 type regulator SOLUTION FOUND

[Gachet]

After lots of searching I've finally found a solution to latch up problems with 7800 type reg, and since I didn't found this answer on the forum, I thought I would share. I've tried it and it works flawlessly.

From the ST PDF datasheet:

 

[Majestic12]

The same solution can be found in an old Elektor book (303 circuits).

 

[Gachet]

It's nice to have confirmation
I've struggled so many times with that problem...

 

[JohnRoberts]

Another remedy is to put diodes in series with the ground leg. While that gives you .5V more output.

JR

 

[Gachet]

Another remedy is to put diodes in series with the ground leg. While that gives you .5V more output.

JR

I assume you're talking about the ground leg of the reg.
That's good to know, thank you.

 

[JohnRoberts]

Another remedy is to put diodes in series with the ground leg. While that gives you .5V more output.

JR

I assume you're talking about the ground leg of the reg.
That's good to know, thank you.

Yes in series with ground leg...  This is a very old problem and I believe it may have been fixed in later generation 3 terminal regulators.

JR

 

[Gachet]

Maybe I'm not lucky because I had this problem several times, or perhaps "banzaimusic" has a ton of old 7800 type and i'm still buying these. :-\

 

[Cardinen]

Sometimes 1N4001/7 are not fast enough for this application.

i had problems in past with 3 gssl, solved with schokkty 1N5819 instead of 1N4007.

I found some brands of 78xx to be more prone to latchup, the one with S (first from right in photo) in my experience are the worst; Never had a problem with ST brand.

 

[Gachet]

the one with S (first from right in photo) in my experience are the worst;

Yep it's the one I use to get when I order from Banzaimusic 

 

[JohnRoberts]

The 78/79_xx VR are probably popular enough, that some manufacturers have chosen to put the old part number on a newer part, even if it is different and better, to get the easy sales from people buying the common part. Kind of like modern 2N3055 are not the same as legacy parts.

JR