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Author Topic: note about tantalum capacitors (I'm a moron)  (Read 1521 times)

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Offline AdminTopic starter

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note about tantalum capacitors (I'm a moron)
« on: July 12, 2010, 09:03:53 AM »
The minus sign on tantalum capacitors connects to the positive part of your circuit, *not* ground. Took me all weekend to figure out why my circuit wasn't working :'(

The clue is that when you have it reversed, it'll short your circuit. The short will typically cause your voltage regulator to dramatically drop in voltage. You will not however be able to detect the short using a multi-meter - it'll look fine until you apply power to your circuit.

I've used tantalums many times in the past, including on the Axon II, but this is the first time I've used one with a marking on it . . .

Offline Invicta

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Re: note about tantalum capacitors (I'm a moron)
« Reply #1 on: July 12, 2010, 11:23:46 AM »

Yep, those Tantalum capacitors can be fussy customers. I reversed, by mistake, the 5v regulated power from my Axon2 to my BlueSMiRF RP-SMA transceiver for only a few seconds and the Tantalum SMD capacitor on the BlueSMiRF was fried  >:( . Luckily I was able to replace it with a Tantalum bead capacitor and all was well  :) .

Yes, any such markings on electrolytic/tantalum caps refer to the positive side.

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Re: note about tantalum capacitors (I'm a moron)
« Reply #2 on: July 12, 2010, 12:48:26 PM »
Fortunately none of my tantalums fried . . . simply reversed them and wallah! Although they could possibly have been damaged, they didn't appear to be . . .


Quote
Yes, any such markings on electrolytic/tantalum caps refer to the positive side.
For electrolytics, the minus sign is for ground :P

Offline Soeren

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Re: note about tantalum capacitors (I'm a moron)
« Reply #3 on: July 12, 2010, 02:57:17 PM »
Hi,

It's not a minus sign and it's generally made a bit too wide to look like a minus sign, but why they didn't change it, one can only wonder. Probably a symbolic fragment supposed to replace the text that used to be on tear drop tantalums - always placed toward the positive pin (the right pin when looking at the text with the pins pointing down).
Regards,
Søren

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Re: note about tantalum capacitors (I'm a moron)
« Reply #4 on: July 12, 2010, 04:05:06 PM »
forgot to mention it was a surface mount . . . but yea, definitely counter-intuitive and a bad symbol choice to mark positive!

Offline waltr

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Re: note about tantalum capacitors (I'm a moron)
« Reply #5 on: July 12, 2010, 04:11:48 PM »
That's another good reason to always read the manufacturers data sheets. Not like I've never gotten caught by something like that.  ::)

Offline Gertlex

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Re: note about tantalum capacitors (I'm a moron)
« Reply #6 on: July 12, 2010, 10:29:59 PM »
But most importantly, do the smd ones make big bangs when they explode, too?

That's the only kind worth using....  ;D
I

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Re: note about tantalum capacitors (I'm a moron)
« Reply #7 on: July 13, 2010, 07:03:37 AM »
But most importantly, do the smd ones make big bangs when they explode, too?

That's the only kind worth using....  ;D
https://www.reliabilityanalysislab.com/tl_hd_0303_tantalumCaps.asp


On my first Axon II prototype I accidentally shorted both tantalum ends with a blob of solder and then powered it up. I think the heat from the short - which was external to the device but still in direct contact - caused the explosion . . .

 


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