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I'm currently designing a PCB in Eagle to build my own Nixie Clock. I know kits exist but I'm trying to do this from the ground up to get the experience. Nixie Tubes require 180V and I'm trying to mimic and existing SMPS Circuit (the bottom of the page has a parts list) but this was designed years ago and a lot of the parts it used are no longer available.

For Example C1: TPSD107M035 it is 100uF with a voltage rating of 35V with a comment saying to use the lowest ESR available. I'm trying to use SMD packages and I'm having trouble finding the part in Eagle. Only a handful of parts have 100uF and 35V voltage rating but they don't list the package type so I don't know what to set it as. This capacitor seems like it would work as a replacement but I cannot find its package information and I don't know if just matching 100uF and the voltage rating is all I need to do.

Would a higher voltage rating work as well? I know there is also polarized vs non-polarized capacitors exist but does that make a difference in most application?

Appreciate the help!

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  • \$\begingroup\$ Yes higher voltage rating works as well. It's the highest voltage allowed to apply. In your application (C1) you can use a non-polarized or polarized \$\endgroup\$ – Botnic Mar 7 '16 at 10:17
  • \$\begingroup\$ So then any 100uf capacitor with a voltage rating of 35 or above would work? I know there was a comment about lowest ESR but I'm not sure how important that is or what value would be considered a low ESR? \$\endgroup\$ – user3055889 Mar 7 '16 at 10:26
  • \$\begingroup\$ ESR is the "Qualitiy" of the Capacitor. It tells you how high the internal resistance is. The lower, the more current it can provide. I don't think it will make a big difference in your application. More intressting for you is the ripple current. This should be higher than the current you expect to flow (2A i quess). This value is quite bad in your CAP (of course the ripple current and the ESR are physically connected) \$\endgroup\$ – Botnic Mar 7 '16 at 10:35
  • \$\begingroup\$ If you select only the cap with ripple current of more than 2 A you see that they all have a ESR of 20-30m Ohm \$\endgroup\$ – Botnic Mar 7 '16 at 10:36
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I'm having trouble finding the part in Eagle

You don't find parts in Eagle, you make them. By the time you carefully vet a part made by someone else, you could have made it yourself. Then it will adhere to your conventions for BOM attributes, documentation layer, assembly drawing, etc.

Would a higher voltage rating work as well?

This is a very basic electronics question, separate from your Eagle question. However, yes, capacitors must be rated at least for the specified voltage, but can exceed it.

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  • \$\begingroup\$ +1 for recommending making your own libraries. There are many advantages of doing it yourself. \$\endgroup\$ – DerStrom8 Mar 7 '16 at 13:14
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The part you have identified as a potential replacement has all the information in the datasheet.

To get the dimensions:

Get the configuration for φd CL configuration

Now get a package (Second one down in datasheet as the one above has identical dimensioning for footprint).

Package

Now find the size to use which is 8 x 10 for this case:

size table

Now get the dimension mapping: Dimensions

The A, B and so forth map to the package dimensions.

The original part has clearly been discontinued. It is an AVX TPS Series part in a size D case, but no longer shows up in the datasheet in the 35V section.

Note that I would not use a 35V tantalum part where the voltage can go up to 30V. Manufacturers suggest derating by 50% to 60% under normal operating conditions.

The ESR of a capacitor in this particular position determines the ripple current it can handle. Note that the ripple current a tantalum can deal with is frequency dependent (it increases with frequency), although a tantalum device has an unusual capacitance curve.

If you can live with the predicted failure rate, then you could, alternatively, use 2 TPSE476M035#0200 in parallel. That decodes to TPS series, Size E case, capacitance = 476 (47μF), 10% tolerance (M), 35V rated voltage, 200mΩ ESR. The allowable 100kHz ripple current is just over 900mA per device.

That would yield a 94μF. 100mΩ ESR device. If you need a lower ESR, use 3 x 33μF parts in parallel (select the lowest ESR in the tables in the datasheet).

I would more likely use a 50V rated part, using parallel parts to get the required capacitance.

Low ESR is somewhat subjective, but 200mΩ is relatively low for a tantalum device. Ceramics can be as low as a few mΩ.

A higher rated voltage is fine, and this part does not seem particularly critical for capacitance value (it is a bulk input filter).

On polarised vs. non-polarised - it depends on the application; here either type could be used provided you keep the polarity correct for a polarised part.

http://www.avx.com/docs/techinfo/Tantalum-NiobiumCapacitors/TANTALUM_MODEL.pdf

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  • \$\begingroup\$ I tried looking in the data sheet a few times but I didn't see what I was expecting to find for packaging info. In Eagle I'll have ex. C01005 package but I don't see anything in the data sheet that shows a number like that. I see where they break down the manufacture number and show GS as the packaging code but do I then need to take GS and compare it with a table the manufacture has elsewhere? \$\endgroup\$ – user3055889 Mar 7 '16 at 11:21
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    \$\begingroup\$ Don't only trust Eagle parts. The Eagle libraries are not exhaustive, and most likely will not have the part you want. You'd be better off creating your own Eagle library. \$\endgroup\$ – DerStrom8 Mar 7 '16 at 13:13

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