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Caps caps caps...

F

Fred Bartoli

Jan 1, 1970
0
You've guessed, I need a cap... (or maybe several if one is impossible)

No Esr spec (ultra low power)
Low cost, as much as possible (by the 10^6 truck load)
Low voltage Vmax=4V
Cap = 220/330/470uF (may I dream 1000?)
Temp range 0-70°C

So far, so good.

Now, I want it ultra low leakage, possibly below the 1µA level over the
temp range...
No wear out mechanism and ultra low FIT: product life = 20 years, 24/24,
no possible service,...

And the customer will want dual source, yeah...

Any thought?
 
F

Fred Bartoli

Jan 1, 1970
0
Fred Bartoli a écrit :
You've guessed, I need a cap... (or maybe several if one is impossible)

No Esr spec (ultra low power)
Low cost, as much as possible (by the 10^6 truck load)
Low voltage Vmax=4V
Cap = 220/330/470uF (may I dream 1000?)
Temp range 0-70°C

So far, so good.

Now, I want it ultra low leakage, possibly below the 1µA level over the
temp range...
No wear out mechanism and ultra low FIT: product life = 20 years, 24/24,
no possible service,...

Should have said :
No wear out mechanism and _ultra low FIT_ : product life = 20 years,
24/24 operation, expected installed base = 10M, no possible service,...
 
Fred Bartoli a crit :





Should have said :
No wear out mechanism and _ultra low FIT_ : product life = 20 years,
24/24 operation, expected installed base = 10M, no possible service,...

Sounds like a ceramic cap.

That's a lot of uF for a uW supply though. 100uA = 1V/S from a 100uF
cap., which is only 1mV ripple if you switch at 1kHz.

Frequent, short pulses into a smaller filter cap might be worth
considering.

I've designed discrete microwatt boost converters. That's probably
easier cap-wise, 0.5 x CV**2 and all.
 
F

Fred Bartoli

Jan 1, 1970
0
Phil Hobbs a écrit :
Polymer aluminums, e.g. http://tinyurl.com/c2ejf5x , would get you some
of that, but not all (at least not guaranteed).

At the qty level I guess it's a no-no, but I'll have to check what the
customer say...
You can get 100 uF MLCCs, e.g. http://tinyurl.com/ctrl7zh .

A couple of those in parallel might get you there.

Thanks for the hint. I didn't look because I thought the 100uF were only
of the Y5V-Z5U ilk...

I'll have to check what they're worth though. On a previous design I've
found some 1uF/10V 0402 X7R loose their capacitance with voltage rather
quickly, almost like the Y5V :-(

A bit nervous with chip cracks too... (but the board is smallish)
 
F

Fred Bartoli

Jan 1, 1970
0
[email protected] a écrit :
Sounds like a ceramic cap.

That's a lot of uF for a uW supply though. 100uA = 1V/S from a 100uF
cap., which is only 1mV ripple if you switch at 1kHz.

Oh, I'm way higher in power, at the mW level :)
Switching at 100kHz, but it's not a bypass cap, rather a reservoir cap
here. Sorry can't say too much...
Frequent, short pulses into a smaller filter cap might be worth
considering.

I've designed discrete microwatt boost converters. That's probably
easier cap-wise, 0.5 x CV**2 and all.

Indeed, but I'm bucking it down later and efficiency is a real big
concern...
 
F

Fred Bartoli

Jan 1, 1970
0
Phil Hobbs a écrit :
Maybe you can rout out a C-shaped strain relief around it, as with
voltage references.

Excellent idea! Thanks.
 
[email protected] a crit :












Oh, I'm way higher in power, at the mW level :)

mW? Monster!
Switching at 100kHz, but it's not a bypass cap, rather a reservoir cap
here.

Naturally. Who uses 330uF bypass caps?
Sorry can't say too much...

Oh yeah, 'twas a current source, right? So that's current ripple.
Indeed, but I'm bucking it down later and efficiency is a real big
concern...

I used discrete components expressly for high efficiency. (All the
commercial controller chips would've drawn several times the intended
load power--no one made efficient controllers for a 20uW supply.)

I'd think a good CMOS totempole would be an awfully good head-start on
a synchronous mW buck, but I haven't actually tried.
 
The loss of C with V goes with volume--bigger caps used at a fraction
of rated voltage are far less affected. Still, I'm surprised to hear
that of X7R--I've not seen that. But then I've not personally seen a
1uF/10V 0402 either.
Maybe you can rout out a C-shaped strain relief around it, as with
voltage references.

Sweet.
 
J

Joerg

Jan 1, 1970
0
Phil said:
Maybe you can rout out a C-shaped strain relief around it, as with
voltage references.

But be careful. This can also cause a cantilever vibration at the end of
a fall, and hair-crack the ceramic.
 
If you need a lot of reservoir cap, and you need to step down, maybe you could
consider an all-capacitor charge-pump type converter, with some CMOS analog
switches and a bunch of ceramic caps. They can be very efficient at low power
levels. It would be interesting to design one that put all the caps in parallel
after they were pumped up, or rather pumped down.

Lots of switches, lots of switches to drive. But that might work,
since he's really making a current source.

As an alternate, he might be able to dispense current 'packets' via a
cap[*], and smooth the doses with an inductor. That would be very
efficient.

[*] like V-to-F's and A/D's.
 
L

legg

Jan 1, 1970
0
[email protected] a écrit :

Oh, I'm way higher in power, at the mW level :)
Switching at 100kHz, but it's not a bypass cap, rather a reservoir cap
here. Sorry can't say too much...

If it's a reservoir you're looking for, you might try storing at a
higher voltage, and only use the part and energy stored, when needed.
The storage could be performed over the long term, not drawing
significantly on power consumption, and not effecting efficiency, once
charged.

Switch into buck reg when needed.....

RL
 
You've guessed, I need a cap... (or maybe several if one is impossible)

No Esr spec (ultra low power)
Low cost, as much as possible (by the 10^6 truck load)
Low voltage Vmax=4V
Cap = 220/330/470uF (may I dream 1000?)
Temp range 0-70°C

So far, so good.

Now, I want it ultra low leakage, possibly below the 1µA level over the
temp range...
No wear out mechanism and ultra low FIT: product life = 20 years, 24/24,
no possible service,...

And the customer will want dual source, yeah...

Any thought?

Not to answer your question, but I do have some thoughts.......
(at least on the days when I'm not in senile mode).

My thought today is to change all circuit boards. In the old days,
tubes had sockets because they failed often. These says the caps are so
lousy, that they need to be replaced often. Therefore, all caps should
have sockets, rather than being soldered in. Then the corner drug store
should have a cap tester where you take your caps to be tested, and buy
new replacements for those that check out bad.
 
F

Fred Bartoli

Jan 1, 1970
0
Jan Panteltje a écrit :
Yes I did read that one,
the modern NSA brain control transmitters are in underground spaces,
those beam upward, and then the tinfoil cap focusses the beam IN the brain.
Have you felt pro US govermnment lately?
Make sure there is no tin foil in your cap!
Some Shampoos also reflect..

Bollocks...

(roasted bollocks, of course)
 
S

Spehro Pefhany

Jan 1, 1970
0
I recall octal-based, plugin electrolytic caps.

Don't remember those. I do remember octal-base mercury relays that
looked like tubes.
 
F

Fred Bartoli

Jan 1, 1970
0
[email protected] a écrit :
The loss of C with V goes with volume--bigger caps used at a fraction
of rated voltage are far less affected. Still, I'm surprised to hear
that of X7R--I've not seen that. But then I've not personally seen a
1uF/10V 0402 either.

Just did the measurement again as I couldn't find it back...

That one:

http://www.digikey.com/product-detail/en/C1005X5R1C105M/445-4979-1-ND/2093593

I misremembered and it was rather one 1uF/16V-X5R-0402 that I measured

Measurements done @10kHz
DC bias Value
0V 808nF
2V 705nF
4V 475nF
6V 320nF
8V 230nF
10V 180nF
15V 110nF
20V 80nF

It also show a pretty high dependency on frequency:

Freq @0V DC bias @6V DC bias
10K 803n 310n
20K 765n 295n
40K 735n 284n
100K 700n 275n
200K 680n 270n
400K 670n 268n

I can't measure at the 1kHz specified frequency right now, but IIRC the
value was spot on at that frequency...

Also, at 3 to 7ohm depending on conditions, ESR surely is not something
to brag about.

I finally resorted to use 470nF caps which behaved better at the wanted
working voltage...


Time to order some and see how the 100uF ones behave...
Maybe not so bright a solution as it first seemed :-(
 
I recall octal-based, plugin electrolytic caps.

I have some very old tube power amplifiers that have them. Back in the
70's I needed replacements and found an old electronics store that still
had some on the shelf. I bought all of them he had. I have not fired
up those amps in years, but still got them.
 
No, I thought it was actually quite funny! Ohhh, a return to the vacuum
tube days, wouldn't that be WONDERFUL!!!

Jon

I have fond memories of going to the corner drug store with my dad and
testing tubes. I was very young, and dad would ahve them all in a bag,
and it was my job to read the numbers to him so he could look them up on
the chart. (usually a wheel turned to expose the rolled up list).

That's sort of what got me started in electronics as a hobby and an old
tube tester was one of the first instruments I bought. I still have
thatr old tester too.

These days that closeness of family doing things together is lost.
Everything involves calling in some specialist or dropping the tv off as
some place where you never see the repair guy, just a salesman with a
repair book and later a bill.
 
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