LM3478 design gets insanely hot
in [Design]
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From: Joerg on 2 Aug 2008 11:20 JosephKK wrote: > On Thu, 31 Jul 2008 13:43:21 -0700, Joerg > <notthisjoergsch(a)removethispacbell.net> wrote: > >> 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. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: langwadt on 2 Aug 2008 11:49 On 2 Aug., 17:20, Joerg <notthisjoerg...(a)removethispacbell.net> wrote: > JosephKK wrote: > > On Thu, 31 Jul 2008 13:43:21 -0700, Joerg > > <notthisjoerg...(a)removethispacbell.net> wrote: > > >> 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. > there numerous different kinds from the neutral almost like vodka, to those with a strong taste of caraway or dill Many will keep it in the freezer, so theres ice on the bottle and it is thick as cream, but thats only if you don't like it :p red Aalborg, pickled herring on rye bread with curry dressing and onions is the start of any real lunch in Denmark, one glass for each leg and a few for the third just to make sure the fish has something to swim in :) -Lasse
From: Joerg on 2 Aug 2008 13:10 langwadt(a)fonz.dk wrote: > On 2 Aug., 17:20, Joerg <notthisjoerg...(a)removethispacbell.net> wrote: >> JosephKK wrote: >>> On Thu, 31 Jul 2008 13:43:21 -0700, Joerg >>> <notthisjoerg...(a)removethispacbell.net> wrote: >>>> 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. >> > > there numerous different kinds from the neutral almost like vodka, to > those with a strong taste of caraway or dill > > Many will keep it in the freezer, so theres ice on the bottle and it > is > thick as cream, but thats only if you don't like it :p > > red Aalborg, pickled herring on rye bread with curry dressing and > onions > is the start of any real lunch in Denmark, > one glass for each leg and a few for the third just to make sure the > fish > has something to swim in :) > I'd prefer saltrulle with it. Of course you need to know someone from Sweden who goes elk hunting every year. Oh, and people with high blood pressure should probably avoid that since it is extremely salty. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: JosephKK on 3 Aug 2008 14:19 On Sat, 02 Aug 2008 08:20:47 -0700, Joerg <notthisjoergsch(a)removethispacbell.net> wrote: >JosephKK wrote: >> On Thu, 31 Jul 2008 13:43:21 -0700, Joerg >> <notthisjoergsch(a)removethispacbell.net> wrote: >> >>> 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.
From: JosephKK on 3 Aug 2008 14:23
On Fri, 1 Aug 2008 14:05:06 +0200, "Henrik [7182]" <not.valid(a)nowhere.dk> wrote: ><langwadt(a)fonz.dk> skrev i en meddelelse >news:cae888a6-c839-4051-9f70-6ad28b0bfaf1(a)k30g2000hse.googlegroups.com... >> The datasheet I just checked had an example with 5V/1A it uses a >> 50mOhm Rsense >> With a typical Vsense at 165mV thats 3.3A and it that must be lower >> than the >> maximum current rating for the inductor. >> >> So why did you choose 7mOhm ? >> >> -Lasse > >Actually I been trying to experiment a little with Rsense today, and what >happes does not make me happy at all :-( > >Everything above 20mR will not yield the 24V output when the load is a 24R >resistor and the input fall below 24V. With 7mR i can obtain my 24V output, >but at the cost of the insanely hot construction :-) > >With no lad, the output is fine, but when I load the output, the voltage >drops. > >Something else is wrong with my setup I think, but I cannot figure it out. I >have some ugly spikes at the FB pin and suspect that these might have >something to do with my problems, but I don't really know how to move on >from here. > >Best regards >Henrik > One thing that has bothered me is the high frequency ringing on the source trace. Is it a measurement issue or is something else going on? |