Tantalum replacement options... - Page 1
Forum section: electronics / projects

author: b9creations
author_rank: Contributor
timestamp: June 28, 2015, 07:21:34 am
content: Hello,I am wanting to build this circuit and noticed the 1uF Tantalum cap in the diagram:http://chemelec.com/Projects/Car-Coil/Car-Coil-1.pngWould a 50V ceramic disc be OK as a substitute? Was hoping to create a reliable circuit with high long-term endurance, that won't catch on fire.. : )I have read many posts here and on the web regarding the tants but was hoping for some expert advice in this specific circuit if possible.Thanks I am a newbie to building circuits, any and all advice or comments are greatly appreciated!Thanks a bunch!

author: tautech
author_rank: Super Contributor
timestamp: June 28, 2015, 07:27:21 am
content: Link requires fixing.

author: b9creations
author_rank: Contributor
timestamp: June 28, 2015, 07:31:24 am
content: Thanks, should be working now....1uF tant is on the far left.

author: tautech
author_rank: Super Contributor
timestamp: June 28, 2015, 07:57:08 am
content: Think about why a Tantalum was specified.......Speed.Also there is a need for some decoupling and bulk capacitance.2 options:Use a 50V Tantalum, always use 50V Tantalums but resist exceeding 2/3 their rated voltage.ORAn electrolytic plus 0.1 uF ceramic in parallel.Fast capacitance is required to catch the nasties created by the switching entering the circuits supply.Personally I'd install it close to the 12V source after the 56 Ohm resister and select a larger capacitance value.

author: Siwastaja
author_rank: Super Contributor
timestamp: June 28, 2015, 08:02:39 am
content: Ceramic or plastic film will work fine; it's most important to put it as close to the IC pins as possible.A parallel combination of a smaller (but at least 0.1 uF) ceramic/plastic and a larger electrolytic (like 10 uF or even more) is most universal if you are unsure about the nature of transients.

author: Karel
author_rank: Super Contributor
timestamp: June 28, 2015, 08:11:37 am
content: I avoid as much as possible electrolytic and tantaliums in my designs.Up to and including 1 uF I use always ceramic caps.As a rule of thumb, the smaller the cap, the better the high frequency properties (less inductance).There are even 10 uF ceramic caps in smd available (Y5V), make sure the voltage rating is much higher thanthe real working voltage because the capacity decreases with higher working voltage.Only exception is for low-freq. / audio applications. There you want to use polyprops.

author: SeanB
author_rank: Super Contributor
timestamp: June 28, 2015, 08:18:05 am
content: Use a 100uF 25V electrolytic, in this application a larger capacitor is better, especially with a 555 timer. Value is not really critical, but here you must use a CMOS version of the 555, like the 7555, as the bipolar version will not operate correctly with the 56R resistor in the supply.fixed the image for you.....

author: Siwastaja
author_rank: Super Contributor
timestamp: June 28, 2015, 08:32:29 am
content: Karel,You may want to look at my recent topic about MLCC failure if you think that a big, high-capacitance SMD ceramic is a robust alternative for electrolytic. The PCB and soldering both need to be spot-on.I understand avoiding tantalums; they do have the problem with current transients, people are not 100% sure if today's tantalums are better than those that blew up back in the day with no reason. They are expensive, use politically problematic material, and do not offer anything special which couldn't be replaced with other types (except some special cases).But also avoiding aluminium electrolytics is just crazy; proper parts from good manufacturers, rated correctly, are very robust in providing bulk capacitance. They do have bad reputation, but it is because of failures at the design, sometimes even intentional - the elcaps have failure modes known so well that they can be used as timers to trigger a product failure after the warranty period.But if you are not designing a switch mode PSU or a DC/DC converter, this won't be a problem. Just use a proper Japanese/Korean brand, preferably one specified to 105C operation, with lifetime of 5000 hours or more at 105C and specified ripple current -- and in most of the applications like this, the actual ripple current will be almost nothing, and the cap won't heat up internally at all. You can get 40-50 years of operation out of it. You don't need to fear about small voltage transients, or irregular current transients. The only thing that really kills these is continuous overcurrent at tens or hundreds of kHz for months or years, or a very hot environment (next to a heatsink at 100C).

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 28, 2015, 08:54:43 am
content: Quote from: Karel on June 28, 2015, 08:11:37 amAnd X5R , which is much more sensible.For higher values, aluminium polymer caps are good, available in similar packages to larger SMD tants, and have insanely low ESR, but quite expensive.

author: acbern
author_rank: Frequent Contributor
timestamp: June 28, 2015, 12:26:44 pm
content: I usually replace Tantalums by Oscons

author: nctnico
author_rank: Super Contributor
timestamp: June 28, 2015, 12:44:04 pm
content: There is one caveat when replacing tantalums with MLCC. Some regulators (the LM1117 for example) don't work very well with a ceramic capacitor. In those cases I put a 0.47 Ohm resistor in series with a 10uf MLCC or place the 10uf MLCC far away.

author: b9creations
author_rank: Contributor
timestamp: June 28, 2015, 03:21:56 pm
content: Wow, thanks everyone for your contributions. I had no idea there were so many folks willing to help! I think I may be even more confused than when I started, but the big revelation being the fact that powering the 555 with less than 12Volts is not ideal, so perhaps this entire circuit was created by an amateur like myself and it's not going to be long term reliable for the application like I was hoping. Don't know enough about electronics to do this myself so perhaps in the end it's going to take hiring a professional to get the job done properly. But I haven't given up yet! : )The saving grace is that I do have a working similar schematic of a professionally done proven reliable circuit which is exactly what I need, however it runs on AC and was would rather go with external DC power supply. With some trail and experimentation, I should be able to figure out the conversion for that one, based on comparing it to this, I guess that's going to be my best bet, given that any potential failures are unacceptable as was hoping to produce lifetime reliable product or as close to that as possible.The only drawback on that one is the transistor is now obsolete, but perhaps the IRF640 in this circuit would work as a replacement? But feels like I should be able to find something that will that's modern and also available in SMD. I have looked at the data sheets for both but the only values that I can comprehend are voltage and amps so maybe when I get to that point I can ask for more help. : ) I also greatly appreciate finding out about the 7555, will look into that as well!You electronic wizards are all my heroes, extremely thankful for sharing your expertise advice and opinions!Kind regards, Jeff

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: June 28, 2015, 05:49:08 pm
content: Just head to digikey and see all the new types.http://www.digikey.ca/product-detail/en/EEH-ZA1H100R/P15441TR-ND/3088124There's a nice app note in that link.

author: schwarzrmsu
author_rank: Contributor
timestamp: June 28, 2015, 09:46:38 pm
content: If this is for an automotive application I would make sure you use X7R rated caps. They will maintain their capacitance over large temperature ranges which is needed in automotive applications. This adds a little bit of cost, but its not a game changer in most cases.

author: G0HZU
author_rank: Super Contributor
timestamp: June 28, 2015, 09:58:32 pm
content: As I've mentioned in previous threads, I've been designing complex defence related (usually comms) products using tants for over 25 years. In acceptance testing and also in the field these get used across a huge temperature range and it isn't uncommon for me to use dozens of tants on a PCB design. These various designs get produced in the thousands and if I thought there was a problem with using tants I'd stop using them.Providing you stick within the recommendations for designing with tants they are very reliable and give good performance. However, it's easy to make tants look bad if you use them inappropriately.

author: EEMarc
author_rank: Regular Contributor
timestamp: June 29, 2015, 06:03:15 am
content: Quote from: Karel on June 28, 2015, 08:11:37 amFriends don't let friends use Y5V. If the temperature is much different than 25C, it is hardly a capacitor at all.As far as replacing Tantulum with Ceramics, the only problem that I have run into is Linear regulators. Ceramics have low ESR. Some linear regulators require higher ESR in order to remain stable. In this case, I've seen resistors in series with a ceramic capacitor to add in some additional resistance.

author: b9creations
author_rank: Contributor
timestamp: June 29, 2015, 07:44:26 am
content: Thanks guys, all helpful info! Greatly appreciated!

author: tszaboo
author_rank: Super Contributor
timestamp: June 29, 2015, 07:59:58 am
content: Quote from: acbern on June 28, 2015, 12:26:44 pmDitto. Also Panasonic and others started making molded Elcos with the same shape size footprint and elecrical characteristic as tantalum, so you can change it without touching a layout.

author: coppice
author_rank: Super Contributor
timestamp: June 29, 2015, 08:02:08 am
content: Quote from: G0HZU on June 28, 2015, 09:58:32 pmMil spec tantalums have very little in common with the tantalums used in most consumer applications.

author: Zero999
author_rank: Super Contributor
timestamp: June 29, 2015, 08:05:06 am
content: Quote from: G0HZU on June 28, 2015, 09:58:32 pmI agree.I also find tantalum capacitors are much more reliable than electrolytic capacitors, providing they're used properly.

author: G0HZU
author_rank: Super Contributor
timestamp: June 29, 2015, 04:00:11 pm
content: Quote from: coppice on June 29, 2015, 08:02:08 amFWIW I nearly always use commonly available SMD solid tants that can be purchased from the likes of Farnell. These are cheap parts usually costing under £0.20 each and they have a very wide temperature range and very good performance. They aren't described as MIL spec parts.

author: coppice
author_rank: Super Contributor
timestamp: June 29, 2015, 04:41:53 pm
content: Quote from: G0HZU on June 29, 2015, 04:00:11 pmDo you mean for prototyping or for production? If its production, how do you get away with that in defence products?

author: b9creations
author_rank: Contributor
timestamp: June 29, 2015, 05:23:51 pm
content: Great discussion guys! Am learning tons from all input! Small quantities to start with so probably start this project out with through hole. Machinist for a living so have access to CNC mill for DIY circuit boards.I found these and couldn't resist trying them out, seems like a descent price for mil spec tants that likely don't go boom.http://www.ebay.com/itm/231183290442They are obsolete though, but if all goes well can switch to solid state type SMD later...Maybe this circuit still has a chance after all.Best regards, Jeff

author: G0HZU
author_rank: Super Contributor
timestamp: June 29, 2015, 05:37:11 pm
content: Quote from: coppice on June 29, 2015, 04:41:53 pmFor production.It isn't really a case of getting away with anything. Defence related products are very diverse and have varying requirements specs.

author: SeanB
author_rank: Super Contributor
timestamp: June 29, 2015, 06:38:31 pm
content: Not every thing in military and aerospace requires you to have paperwork tracing things back to when the shovel first hit the ore, and who was holding it, the model and serial number of the shovel and which hand he was using at the time. some are more relaxed, you just have to be able to say which factory made it, when and with certainty which machine made it. Sometimes you just have to know who made it.