G
George Herold
Guest
On Jan 31, 2:51 pm, John Larkin <jlar...@highlandtechnology.com>
wrote:
themselves.
or they screwed up. There's this very tiny (+) sign on the tant.
(through hole)
George H.
wrote:
Well some can run at ~ -12V (-33%) for several hours before cookingOn Mon, 30 Jan 2012 19:58:18 -0800 (PST), George Herold
gher...@teachspin.com> wrote:
On Jan 30, 10:32 pm, "k...@att.bizzzzzzzzzzzz"
k...@att.bizzzzzzzzzzzz> wrote:
On Mon, 30 Jan 2012 19:18:41 -0800 (PST), George Herold
gher...@teachspin.com> wrote:
On Jan 30, 10:18 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On 28 Jan 2012 20:48:21 GMT, Jasen Betts <ja...@xnet.co.nz> wrote:
On 2012-01-26, Tim Williams <tmoran...@gmail.com> wrote:
On Jan 25, 9:55 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
I don't exactly understand the situation. Got a sketch?
Does this involve tantalum caps?
A description should suffice [rum disclaimer inserted here]:
Yes -- I have eight output transformers in parallel from the same
current-limited PWM driver. Now, under normal conditions, all eight
channels are working correctly, so the current shares evenly, and all
the caps are happy (the maximum supply is 5A, so they each see a
maximum of 5A / 8 = 0.6A peak, so the RMS ripple is under 0.42A, fine
for a chip tantalum, though I have ceramic specified at the moment).
But under fault, the whole 5A could flow into just one channel, which
makes things "interesting". I may implement a "max-of-channels"
current limit for this.
Under this fault condition in the fault current passing through the
tantalum cap, or just visiting the neighbourhood?
energy density detonates tantalums, don't get them hot and
charged at the same time.
What usually detonates them is high peak current, or equivalently high
dV/dT.
--
John Larkin, President Highland Technology Incwww.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators- Hide quoted text -
- Show quoted text -
No, the worst thing about tant. caps is they get put in bakcwards*,
*MANY* moons ago, my boss was the Tantalum Cap Tzar for the corporation (how
he got that "distinction", I haven't the foggiest). We were having all sorts
of problems with fires caused by tants in backwards. Everything was tried,
three pins (-+-), four pins (-++-), big lead/little lead, fuses, everything.
No matter what, something like 1% of them got stuck in backwards (even to the
point that when all else went right 1% were in the tubes backwards).
One day the manager of the local manufacturing/stuffing department called
complaining that his "girls" were getting sore thumbs from sticking the
capacitors into the boards. Yep, they were big/little lead caps and they were
trying really hard to put the big lead in the little hole. They'd done a few
thousand that way.
I spent an hour today, trying to figure out why the current limit
kept turning on, at ~3 volts, but only under a good load???
I had a bunch go off about 2" from my ear, while I was leaning over the bench
try to figure out why the supply was limiting (I always brought systems up the
first time with the supply in constant current mode).- Hide quoted text -
- Show quoted text -
Yeah... a backwards cap finally 'dawned' on me and it took less than
30 seconds to lay my fingers on the problem. New run... they're all
in backwards, except for a few I guess.
Does under voltaging (sp) make a few last longer?
I swear I've had stuff powered up for few hours, and then get pictures
sent of a 'brown' tantalum, in backwards.
(Return costs are expensive, but ya gotta take care of your
customers!)
George H.
Conventional wisdom is that tantalums can run at -3 volts or -10% of
rated voltage, whichever is more. Or less maybe.
themselves.
It was a mistake. Either we gave the board house the wrong polarityWhy put them in backwards?
or they screwed up. There's this very tiny (+) sign on the tant.
(through hole)
George H.
**********************************
John Larkin, President
Highland Technology, Inc
jlarkin at highlandtechnology dot comhttp://www.highlandtechnology.com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation- Hide quoted text -
- Show quoted text -