<azonenberg>
graduated in microns and accurate to +/- 2 or 3
<azonenberg>
lol
<azonenberg>
this is a nice mitutoyo
<Thetawaves>
dial indicators swing about an axis to allow you to check flatness
<azonenberg>
best measuring instrument i ever used
<azonenberg>
and i align optically
<azonenberg>
remember my exposuire system doubles as a microscope ;)
<azonenberg>
So i just turn the lamp down low and align the projected image to the features on the wafer
<azonenberg>
then turn it up high to expose
<Thetawaves>
i think it would be a valuable tool
<azonenberg>
might be, but i dont have one yet
* azonenberg
looks at clock
<azonenberg>
almost 0600 here lol
<azonenberg>
And the rest of this stack of exams isn't getting graded while i'm as sleepy as i am now :p
<Thetawaves>
hah
<Thetawaves>
good night
<azonenberg>
Good night? It's six in the morning :p
* azonenberg
AFKs
* bart416
drags azonenberg back in here
<bart416>
LTSpice is remarkably fast at simulating amplifiers :S
<bart416>
6ms/s...
berndj joined #homecmos
<bart416>
These guys designed their PCB with the assumption that there are x% of cold joints I'd say :S
Helldesk joined #homecmos
<azonenberg>
bart416: what??
<azonenberg>
redundant links or something?
<bart416>
yes
<bart416>
all the diodes in the protection circuits are in parallel
<bart416>
completely useless
<bart416>
except if you're expecting cold joints
<azonenberg>
lol
<bart416>
I traced everything and worked it out somewhat
<azonenberg>
What about for increased current?
<bart416>
And the only reason is cold joints lol
<bart416>
diodes don't work like that though
<bart416>
They'd pop one by one
<azonenberg>
You mean they dont have the exact same Vfwd?
<azonenberg>
Yeah
<azonenberg>
I've seen that happen
<azonenberg>
But maybe the designer doesnt know that :p
<bart416>
On IC level you can put them in parallel actually
<berndj>
i've seen people claim that diodes do share current nicely
<berndj>
not that i'm convinced...
<azonenberg>
Maybe at IC level
<azonenberg>
because then you can guarantee consistency to a higher level
<berndj>
yeah, much closer thermal coupling
<azonenberg>
just like parallel transistors are baiscally just a longer channel
<azonenberg>
Well its also consistency in doping etc
<berndj>
*wider, but yeah
<azonenberg>
but not from die to die
<azonenberg>
whcih might have been even on different wafers
<berndj>
i always thought it's primarily about the loose thermal coupling that BJTs and diodes don't share current nicely - because of the negative tempco of Vf
<azonenberg>
I think its mostly related to Vf being different at time=0
<azonenberg>
one of them heats up a little more
<azonenberg>
then you get runaway
<berndj>
otoh, when i measure Vf of random 1N4007s with my multimeter, invariably they're the same to within a few mV
<berndj>
there's probably a critical current above which they stop sharing nicely
<azonenberg>
a few mV though?
<azonenberg>
Thats enouhg
<bart416>
Current takes the path of least resistance as well
<azonenberg>
you heat up by a tenth of a degree
<azonenberg>
Vf changes
<azonenberg>
it heats up even faster
<azonenberg>
you get a positive feedback loop in which this die dissipates more and more power as a function of the total
<azonenberg>
before long, bang
<azonenberg>
i've seen it happen with paralleled LEDs
<azonenberg>
all in parallel with the same series resistor
<azonenberg>
one blew, others were fine
<berndj>
it does, but it also dissipates faster - below a certain current the dissipation actually dominates (IIRC & YMMV - i did this sort of calc for hotspot along the length of a copper wire once, critical current density was maybe a few dozen A/mm^2)
<bart416>
What actually does work to some extent is putting a fast shottky diode in parallel with a regular PN diode
<bart416>
in certain situations that is
<bart416>
you have the fast response from the shottky
<bart416>
and the current capability of the PN diode
<berndj>
how does the current capability of the PN diode even come into play though?
<bart416>
it depends on the circuit berndj
<berndj>
i thought the schottky would destroy itself protecting the PN diode
<bart416>
the thing is, the shottky (aaaaargh c key doesn't work if I type fast and I have to hit it with a sledge hammer) has a higher Vf than the PN in those particular situations
<bart416>
Resulting in the PN diode taking all the current through it
<berndj>
oh - you mean Vf rises faster than a regular diode's does?
<bart416>
A schottky is simply faster at switching
<berndj>
but also lower Vf
<bart416>
As I said, specific situations
<bart416>
I've seen it done in some high power pulsed laser circuits
<berndj>
hah. throw out the rulebook then
<bart416>
not really
<bart416>
it still sticks to the rules
<bart416>
the schottky is activated faster (the voltage is high enough to activate it anyway), but the PN requires a lower voltage in that case resulting in the PN taking the punishment off the schottky within a few microseconds
<berndj>
regular schottkys or those fancy new SiC ones?
<bart416>
Dunno
<bart416>
Sorry, but I don't study the naming of components in detail
<berndj>
i mean the new schottkys where the one half is SiC (wider bandgap) and not plain silicon
<berndj>
let's you have fast switching at 1000V+
<bart416>
Heh, playing with high current GaAs diodes is also fun
<berndj>
ugh. i now realize what "looked wrong" in that "let's"
<bart416>
azonenberg, I think I actually found PCB design software for simple things that doesn't make me want to kill myself :|
<azonenberg>
bart416: Simple things? Yeah
<azonenberg>
It's when you start doing >=4 layer designs with fat parallel buses and differential pairs
<azonenberg>
that it gets tricky :p
<bart416>
Then you just start using OrCAD, ADS or Altium...
<azonenberg>
unfortunately i cant afford any of them lol
<bart416>
Those are the only three that seem to be capable of handling more than 2 layers well
<azonenberg>
expresspcb *can* as long as the two inner layers are just power/ground planes
<bart416>
actually, design spark seems to be capable of more than 10 layers lol
<bart416>
(and not just power or ground planes either it seems :S )
<azonenberg>
But express can't do differential pairs
<azonenberg>
or autoroute
<azonenberg>
I'm looking at kicad and geda
<azonenberg>
havnet made a choice yet
<bart416>
oh but design spark can auto route
<bart416>
Hence, it's awesome
<azonenberg>
i want to do a small 4-layer design in both
<bart416>
And it also seems to be capable of handling eagle libraries at first glance
<bart416>
try design spark, seriously
<azonenberg>
winblows?
<azonenberg>
if so thats a game-over
<bart416>
yeah, it's windows
<azonenberg>
yeah, i am not going to be happy with that :p
<azonenberg>
express at least sort of runs in wine
<azonenberg>
but none of the nice ones do
<bart416>
Try to run it in wine
<bart416>
+ also seems to have some links to spice at first sight
<azonenberg>
and can it export gerber?
<bart416>
looks like it
<azonenberg>
very nice, i'll take a look
<azonenberg>
a FOSS tool would be best of course
<bart416>
Well, I'm not really sure how RS managed to do this :S
<bart416>
This is a direct shot at eagle lol
<bart416>
And at first sight it's head on
<azonenberg>
very nice
<azonenberg>
limited?
<bart416>
Doesn't look like it
<bart416>
well, unless you mean 14 layers is a limit
<azonenberg>
I mean artificially limtid
<azonenberg>
and is it free or commercial?
<bart416>
free, you do need to register but that's it
<azonenberg>
so whats the catch?
<bart416>
and it can "only" do boards up to 1m squared lol
<bart416>
I'm trying to find the catch :S
<azonenberg>
expresspcb limits you to their proprietary CAD format
<azonenberg>
So you can only use their fab service
<bart416>
well, there's gerber export...
<azonenberg>
but its freeware and has no *artificial* limitations
<azonenberg>
though its design sucks and you can't do >2 signal layers plus optionally 2 power planes
<bart416>
At first sight it doesn't look limited at all :S
<azonenberg>
so designspark is free and unlimited
<bart416>
Looks like it
<azonenberg>
But then why arent they releasing source?
<azonenberg>
do they plan to go commercial eventually?