I don't like tants across power rails... they tend to explode. I do use them across linear reg outputs, because the ESR is often just right, but I derate 3:1 on voltage.
Aluminum polymers are nice, very low ESR, no dry-out, no detonation mechanism. Prices are getting more reasonable.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
an smsp draws ~constant power, lower input voltage draws higher input current, with a bit of bad luck the increased current lowers the voltage increasing the current etc. etc.
-Lasee
Methinks you do not know how to read. Thew note clearly reads "47p".
The post-it doesn't "clearly" read anything. The value is obviously 47 uF; the jpeg file name clearly says so. The waveform clearly says so. I say so.
If people were in doubt as to the value, they could have asked. They'd rather bunch up their panties and debate nonsense forever.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Ordinarily I'd love to, but I have no spare time for such frivolities this week I'm afraid. :(
It's characteristic of all type 2 dielectrics. The denser ones (Y5V, Z5U..) just do it worse, which is to say, you're really just cheaping yourself out of more energy storage.
(The higher k means lower energy density: e = D^2 / (2*e_0 * e_r) D is the electric analog of B, and E that of H. Thus, where B = mu*H for magnetics, D = epsilon*E for electrics, and where e = B^2 / (2*mu), the same is true with D and epsilon.)
The sad part is, modern X7Rs (historically a preferred choice, because of the only *moderately* high e_r) exhibit about as much voltage dependence as any other type, because they're better at making thinner, more reliable layers.
The solution is not simply to get a higher voltage rating, because the voltage rating is for breakdown. (Just as a ferrite bead's rating is thermal, not magnetic. Seeing the similarities?) The only solution is to buy physically larger parts (still with a relatively high voltage rating), so that there's more dielectric.
Or buy tantalum, which is just as expensive but catches fire, or aluminum, which expires after a while (polymers have ESR as low as ceramics, so are an excellent substitute, while electrolytics kind of just suck, but both are subject to aging).
C0G has the highest energy density (because guess what, low k!), but only becomes useful in high voltage ratings (>250V), and is impossible to get in massive values. You're kind of stuck if you need fast energy storage in a smaller package than electrolytics.
Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
OK, the 47uF 6.3 volt cap seems fine after several hours at 120 volts. The leakage is very slowly creeping down, now about 50 uA after a few hours.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Typical behavior is that energy storage increases linearly, in the saturation region. So, it still stores more energy with increasing voltage, but not nearly as much as, say, a C0G (which remains parabolic until it physically explodes).
The behavior transitions from parabolic, at the saturation knee. Which you can find in the datasheet (well... when provided). This should be enough direction to estimate the behavior of a given cap.
1uF at 20V is a physical impossibility* in 0402. You'll incur serious inrush or startup speed problems doing that.(*For a much less impossible, linearity-motivated definition of 'impossible'...)
Interestingly(?), electret caps are beginning to be introduced. These were featured in the Google Little Box design:
Notice the C peak at high voltage:
And the price...
Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
Do it all the time. The big thing is to make sure there is enough input capacitance on the supply. Of course, this isn't unique to cascaded supplies. Insufficient input capacitance can cause all sorts of EMI issues, even if it works.
The input of a switching power supply is negative impedance. Lower the voltage and the current goes up - negative resistance.
Hmmm..
Try nudging it with a hot soldering iron, while it's under bias.
Do it carefully while monitoring leakage, so it doesn't run away or anything...
If you can get it up to soldering temp, it should take a 'set' that 'freezes in' at low temperatures.
Then try the square wave again! :)
Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
Um, John's capacitor isn't a capacitor. His scope is indeed a scope. Your analog scope would look as bad, or worse.
That depends on the caps. That's what the datasheets are for.
No, just ripple current, ESR, ESL...
Amazing, really.
Apart from highlighting Cursitor Doom's, Julian Barnes' and John Larkin's frequent idiocies.
-- Bill Sloman, Sydney
As happens remarkably frequently. It would be nice if he paid some attention to the corrections, but he - like Trump - is sublimely self-confident.
-- Bill Sloman, Sydney
John Larkin doesn't think so. Looking at it very carefully, the top of the "p" isn't quite closed, so the hypothesis that it was intended to be a Greek mu (which tends to have a shorter tail) isn't entirely implausible.
-- Bill Sloman, Sydney
On Wednesday, October 19, 2016 at 5:35:35 PM UTC-7, Tim Williams wrote: ...
That doesn't stop manufacturers advertising such components:
eg TDK 1uF 25V 0402
This was at the output of a power limited booster so inrush was fairly gentle and startup conditions were not an issue.
As I mentioned we did find a solution with newly available small form factor tantalums with a small COG in parallel. This also avoided piezo-electric effects that were being troublesome. This was in a VERY space constrained product.
kevin ...
Heisenberg warned everyone that any attempt to measure an attribute will diddle the pre-measured attribute. A 1V delta is worse that a 5V delta; maybe even more than 5 times worse. Use 5 milivolts to minimize the alteration of the actual tc.
Make the measurement in the actual application circuit, disturbing that circuit as little as possible, to get a reasonable idea of the tc in that application. Maybe that value will be close to data sheet spec and maybe not; there is bias dependency, time-from-startup dependency, and other possible traps to fiddle you up.
Even if we allow that strange interpretation, it clearly is NOT 47micro.
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