Confirming the voltage rating of a ceramic capacitor - Page 1
Forum section: electronics / projects

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: April 01, 2025, 12:30:13 am
content: Hi group,I recently bought a reel of 0.1uF 50V 0603 ceramic capacitors from Aliexpress. It is fairly easy to confirm the value of the capacitors. I am going to share the method that I used to confirm that these are really 50V capacitors.The technique relies on the fact that the capacitance of ceramic capacitor changes with bias voltage.I am using an HP4274A this allows the capacitor to be measured with bias voltage.LabelThis is the label that is attached to the reel. I have no idea if they are really Samsung parts.Measurement 1 - No bias voltageWith zero dc bias the measured capacitance is 94nF. This is a reasonable value for 100nF capacitors.With 25V bias voltageI used a Yokogawa 7651 to supply the bias voltage to the rear connector on the HP4274A LCR meter.The reading with 25V of DC bias is 60.4nF.The value of the capacitance has dropped by 40%.Looking at Kemet data for a similar 0603 50V X7R 100nF capacitor:This shows that the value of capacitance should drop by 40%.ObservationThe capacitors that I bought from Aliexpress are 100nF 50V X7R 0603 capacitors.This is a useful technique for confirming the voltage rating of a ceramic capacitor.Regards,Jay_Diddy_B

author: Someone
author_rank: Super Contributor
timestamp: April 01, 2025, 03:21:21 am
content: This is not reliable as many lower voltage parts are simply truncations of the same capacitance vs voltage curve of a higher rated part.

author: mtwieg
author_rank: Frequent Contributor
timestamp: April 01, 2025, 11:00:01 am
content: Capacitance vs DC bias has absolutely nothing to do with the voltage rating of a capacitor. Some class II capacitors retain 80% of their nominal capacitance at their rated voltage. Others retain less than 10%.In practice there is no way to determine the rated voltage of a capacitor, as it's a number assigned by the manufacturer based on their knowledge of process parameters and failure modes.You could test a capacitor at increasing voltage until it fails, but this would be a destructive test, and would just tell you about that specific cap. Many will probably survive far beyond the rating with no problem. Maybe if you did the testing on hundreds or thousands of units (over the whole temperature range), you would be able to work out roughly what their voltage rating should be.

author: RoGeorge
author_rank: Super Contributor
timestamp: April 01, 2025, 12:21:37 pm
content: For an unknown capacitor, I would rather look at the leakage current while increasing the voltage in DC steps, and expect a accentuated increase in leakage once the nominal voltage is reached.I don't know if such behavior is to be expected for ceramic type, too, but I guess it should be. Saying that because I've measured sudden increased in leakage current at DC in electrolytic capacitors, once their nominal voltage was overridden:First posted inhttps://www.eevblog.com/forum/chat/rate-my-42-years-old-2200uf25v-electrolitic-capacitor/Sure, that measurement is for an electrolytic capacitor, and the leakage current increase might behave very differently for ceramics, but I would still expect an increase in leakage at very high E field values (again, just a guess, never tested if this would be true for ceramics).

author: TimFox
author_rank: Super Contributor
timestamp: April 01, 2025, 03:26:50 pm
content: The capacitance vs. voltage test in the original post indicates that the part will operate at 50 V, with a behavior typical of an X7R device.The actual drop in capacitance is a function of the E field (voltage gradient) within the dielectric, not the voltage across it.A manufacturer's maximum voltage specification for such a device is a guarantee that the part will not be damaged at that voltage, not necessarily a recommended operating condition.

author: Siwastaja
author_rank: Super Contributor
timestamp: April 01, 2025, 03:27:02 pm
content: Because nominal voltage does not really mean anything to manufacturers, there also is no meaningful test you can do to obtain it. You can of course invent much better and more sensible definitions for "nominal voltage" than manufacturers do, but since they won't start following your practice,Opening post describes measuring the capacitance vs. voltage curve. Highly useful, and you can of course compare itto the capacitance vs. voltage curveof theexact same capacitor part numberto get an idea if the part is what is being claimed. But the step where nominal voltage is guessed from the curve by looking at some other part from other manufacturer is incorrect and works only by luck every now and then.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: April 01, 2025, 05:05:39 pm
content: Hi,Quote from: Siwastaja on April 01, 2025, 03:27:02 pmThese are good and valid comments.I have found the Samsung data.Here is a link:https://weblib.samsungsem.com/mlcc/mlcc-ec.doFor the capacitor I have:Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: April 01, 2025, 05:12:53 pm
content: Hi,In the original measurement I used an HP4274A LCR meter. I am now going to share a simple circuit that can make the same measurement.Base circuitThis a 555 astable circuit. By operating the circuit at 5V, the voltage on the capacitor 1.6V p-p and 770Hz.Modified CircuitThe circuit is modified to place a bias source in series with the capacitor under test. D1, D2, D3 and R2 provide some protection.The bias voltage is Vbias - 2.5V.The period of the oscillation is proportional to the capacitance.ResultsThe results from the 555 circuit give a good indication of how the capacitance changes with bias voltage.I am not sure if I have genuine Samsung capacitors, but I seem to have useable components.Regards,Jay_Diddy_B

author: johansen
author_rank: Super Contributor
timestamp: April 01, 2025, 05:15:18 pm
content: for extra credit, plot the energy stored in the capacitor as a function of voltage.it is fairly constant. and this is what you would expect from the mechanism by which the capacitor stores charge.

author: RoGeorge
author_rank: Super Contributor
timestamp: April 01, 2025, 06:07:33 pm
content: Quote from: Jay_Diddy_B on April 01, 2025, 05:12:53 pmNice!Worth considering for this the CMOS version of 555 from TI:https://www.ti.com/lit/ds/symlink/lmc555.pdf, which can work powered at only 1.5V (the lower the square wave amplitude, the more precise measurement), and up to 3MHz (the faster, the better for smaller capacitances).

author: Siwastaja
author_rank: Super Contributor
timestamp: April 01, 2025, 06:10:55 pm
content: Quote from: johansen on April 01, 2025, 05:15:18 pmDecaying towards a constant the more it's driven into saturation, you mean.It being even nearly constant would imply nearly infinite capacitance near 0V.These high energy density MLCCs saturate, just like inductors with iron or ferrite core do. This means that initially, energy gained from increasing voltage (current for inductors) rises as expected from E = ½CV^2, but the further voltage rises, the less there is added energy. Additional energy would not go to 0 even at rated voltage, though, and therefore the whole curve energy vs. voltage is still far from constant.Or maybe you meant linear (first order), not constant? Like, instead of E ~ V^2, you mean E ~ V? That would be closer to truth, but still a crude approximation based on observations; I fail to see how this is obvious at all from how these capacitors are constructed.

author: johansen
author_rank: Super Contributor
timestamp: April 01, 2025, 10:02:33 pm
content: Quote from: Siwastaja on April 01, 2025, 06:10:55 pmdo you know how they store energy?

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: April 01, 2025, 11:56:03 pm
content: Quote from: RoGeorge on April 01, 2025, 06:07:33 pmI thought about this, the conditions given on the Samsung data are: 1V rms and 1kHz. 1V rms is 2.8V p-p. The test conditions in the 555 circuit are 1.6V p-p and around a 1Khz, the frequency varies with the capacitance changing.I was surprised that Samsung used a fairly large test signal.I actually used the CMOS version of the 555. I repeated the measurement with the 555 operating from 1.5V.Here is a comparison using a 5V supply voltage and 1.5V supply voltage.There isn't a big differences between the two measurements.Regards,Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: April 02, 2025, 12:49:41 am
content: Hi,Here is a photograph of the test setup. The capacitor being tested was soldered to a scrap of FR4 in the top left of the picture. The 555 is mounted on a dip adapter in the center of the picture.Regards,Jay_Diddy_B

author: Zero999
author_rank: Super Contributor
timestamp: April 02, 2025, 10:24:43 am
content: Quote from: Jay_Diddy_B on April 01, 2025, 05:12:53 pmSPICE is lying to you. That model doesn't model the saturation voltage of the output stage properly. I'll post a better model later. I don't have it on this machine.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: April 02, 2025, 08:15:41 pm
content: Quote from: Zero999 on April 02, 2025, 10:24:43 amYes, SPICE is a simplified model. In this application is doesn't really matter. I am using SPICE to document the schematic.I am not trying to measure the capacitance, I am trying to measure the percentage change in capacitance with bias voltage.Here is the actual waveform, with 45V bias voltage:I am using a CMOS version of the 555. It is pretty close to the ideal waveform.Jay_Diddy_B

author: floobydust
author_rank: Super Contributor
timestamp: April 02, 2025, 09:49:18 pm
content: Aging, even in the first 24h, is a significant factor for MLCC's value being low... and getting lower...As I have mentioned here a few times (a goodsymposiumwrite-up), aging can cause unexpected product failure (i.e. LDO starts oscillating) as capacitance drops. It's caused problems especially for noob engineers specifying the parts- who assume they'll get anything close to rated value.So I would repeat the tests after some time.It's now a spec on datasheets "Aging Rate (Maximum % Capacitance Loss/Decade Hour)". Capacitance measurements (including tolerance) are indexed to a referee time of 1,000 hours."A thermal (soldering) cycle >125C curie resets, causes a "deage" back to new value.sourceI dislike Samsung MLCC because even at 1/2 rated V they are way down. Supplier #3? lol.

author: Zero999
author_rank: Super Contributor
timestamp: April 02, 2025, 09:56:46 pm
content: Quote from: Jay_Diddy_B on April 02, 2025, 08:15:41 pmYes, a CMOS 555 will be better.For future reference here's the model.The schematic. It has a diode and transistor on the output to make it more realistic. I tried two diodes but it wasn't as good. The ideal diode bypassed the transistor, when the 555's output goes low.I then generated a net list by clicking view SPICE net list.I copied it to clipboard, pasted it into a SPICE directive on the schematic and added the .subckt definition..subckt 555 1 2 3 4 5 6 7 8X§U1 1 2 N002 4 5 6 7 8 NE555D1 N002 N001 DD2 3 N002 D_idealR1 8 3 100kR2 3 1 100kQ1 8 N001 3 0 NPN.model NPN NPN.model D D.model D_ideal D(Ron=1m Roff=1G Vfwd=0).lib NE555.sub.backanno.endsEDIT: I've just noticed R4 on the schematic, is R2 on the net list. I think it's due to my copying and pasting it from a different schematic. It doesn't affect the model of course.Here's the simulation.