LM3478 design gets insanely hot

[Joerg]

Dear Joerg,

Thank you very much for your replies. I will with a 50mR or so Rsense
tomorrow, Also I will try to get the scales and such nice info into the
shots.

BTW it makes it easier for others to follow and contribute ideas if you
write below the quoted text.

Also I will try exchanging the sepic capacitor to a large 1uF ceramic
capacitor that I have in stock.

Stack a few of those for the test. 1uF may be a tad too small for a 1A
switcher (tho it'll work). Nowadays you can get pretty good 10uF or at
least 4.7uF caps but even there you may have to parallel in order to
ease and share the current load. They have become quite cheap.

With switchers it is really important to carefully study the datasheets
of even the most mundane parts. We take those caps for granted in bypass
situations but here they'll have to slosh around a lot of energy. I
leaned that the hard way. Everything was fine for an hour or so. Then a
very loud bang, pieces flying around, and what was left from the
ceramic material of a capacitor had turned into green bubbly glass.
Quite pretty actually but it could have been a bad situation if I hadn't
worn eye protection glasses. Best to wear those when you work on
switchers and similar gear that can go "exotherm".

Thank you so very much for your help. I will sleep much better now that I
see a possible solution to my problems ;-)

Since you are in Denmark this would be the perfect time for an ice-cold
shotglass of Aquavit. Good stuff

[...]

Mmmm. Aquavit. Once in a while i get some Aalborg Jubilamus variety
aperitif, sugary but very tasty.

Aquavit isn't sweet. But it has to be served ice cold and ideally the
glassed should be chilled to where ice crystals form when you take them
out. Just make sure you don't have to drive anymore that day.

 

[JosephKK]

Henrik [7182] wrote:
Dear Joerg,

Thank you very much for your replies. I will with a 50mR or so Rsense
tomorrow, Also I will try to get the scales and such nice info into the
shots.

BTW it makes it easier for others to follow and contribute ideas if you
write below the quoted text.


Also I will try exchanging the sepic capacitor to a large 1uF ceramic
capacitor that I have in stock.

Stack a few of those for the test. 1uF may be a tad too small for a 1A
switcher (tho it'll work). Nowadays you can get pretty good 10uF or at
least 4.7uF caps but even there you may have to parallel in order to
ease and share the current load. They have become quite cheap.

With switchers it is really important to carefully study the datasheets
of even the most mundane parts. We take those caps for granted in bypass
situations but here they'll have to slosh around a lot of energy. I
leaned that the hard way. Everything was fine for an hour or so. Then a
very loud bang, pieces flying around, and what was left from the
ceramic material of a capacitor had turned into green bubbly glass.
Quite pretty actually but it could have been a bad situation if I hadn't
worn eye protection glasses. Best to wear those when you work on
switchers and similar gear that can go "exotherm".


Thank you so very much for your help. I will sleep much better now that I
see a possible solution to my problems ;-)

Since you are in Denmark this would be the perfect time for an ice-cold
shotglass of Aquavit. Good stuff

[...]

Mmmm. Aquavit. Once in a while i get some Aalborg Jubilamus variety
aperitif, sugary but very tasty.

Aquavit isn't sweet. But it has to be served ice cold and ideally the
glassed should be chilled to where ice crystals form when you take them
out. Just make sure you don't have to drive anymore that day.

Most are not. The Juibilamus aperitif variety is. It is kind of like
the difference between Scotch and Drambuie.

 

[neon]

You still don't get it 15v to 32v @1A =17w use a pre-regultor of 18v if you must run from a wild input range 15v 32v. the same applies to 120vac I used a 90v regulator to compensate for line drop typical on airplanes power sources. eficiency goes to hell but it works.