How do you choose electronic components.

Thread Starter

camerart

Joined Feb 25, 2013
2,600
Hi,
I'm looking for electrolytic SM Capacitors, and finding it's not so easy.

How do you choose components?

I am finding that each time I choose one, then check the data sheet, I find something that makes this component incorrect. e,g, I've been using a particular capacitor on my 3.3v PCBs, only to find today, that their lowest voltage range is 1v too high.

Cheers, Camerart.
 

BobTPH

Joined Jun 5, 2013
3,484
The voltage rating of a capacitor is the maximum voltage it can handle without damage. You can use any capacitor with a rating higher than needed, leaving a small margin of error. For 3V iI would use one rated at 5V or higher. A 100V rated one would be okay, but would be larger and cost more than necessary.

Bob
 
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Audioguru again

Joined Oct 21, 2019
3,305
I think that Camerart does not know what is the voltage rating of a capacitor. Maybe he thinks::
1) It generates its rated voltage?
2) It limits its rated voltage?
3) it regulates its rated voltage?
Actually, a capacitor does none of these things.
 

Thread Starter

camerart

Joined Feb 25, 2013
2,600
Hi A and B,
When I check capacitors in 'say' Farnell, they only show maximum voltage, say '16v'.
I mainly use 12v, 5, and 3.3v.
When I looked at my chosen capacitor data sheet, is showed min 4v to maximum 16v.
I usually leave a margine above any likely voltage I may use, and understand it needs to be higher, but I have never seen a mimimum voltage.

What I was asking is how do you choose components? Do you always check each component data sheet, before buying, if so it can be time consuming.
Thanks, C
 

MrChips

Joined Oct 2, 2009
23,892
What I was asking is how do you choose components? Do you always check each component data sheet, before buying, if so it can be time consuming.
Thanks, C
I know what you mean. If you go to Digi-Key website and search for a 1kΩ through-hole resistor, there are 2,993 from which to choose. For any component, there are current, voltage, power, temperature coefficient, material, tolerance, size, lead size, orientation, brand, price break, manufacturer, and finally stock and delivery time. In the majority of cases, your experience and circuit application will allow you to narrow the options down to a few hundreds. Price and and stock are usually the clincher. Using filtered search is your ally.

I usually wait until I have a larger number of items to purchase in order to avoid paying shipping charges. Then I can easily spend three or more hours making the right selection.
 

MrChips

Joined Oct 2, 2009
23,892
Min and max values in datasheets can be inconsistent and confusing.
You need to consider what are the limitations of the parameter and whether a low or high value is a good or bad attribute.

Sometimes you might find a min spec being higher that the nominal spec.
As an example, a component rated for 16V may have min 20V meaning that all devices are capable of handling 20V.
 

Thread Starter

camerart

Joined Feb 25, 2013
2,600
Would you mind posting that data sheet, or at least the relevant part.
Hi ES and A and MC,
Here is a data sheet, and now re-reading it, shows the MIN MAX voltage of their range of capacitors, so if I'm correct, it was the way I read it. The one I read earlier, must have said their range was 4 to 16V, so not one cap, but their range.
C
 

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Thread Starter

camerart

Joined Feb 25, 2013
2,600
I know what you mean. If you go to Digi-Key website and search for a 1kΩ through-hole resistor, there are 2,993 from which to choose. For any component, there are current, voltage, power, temperature coefficient, material, tolerance, size, lead size, orientation, brand, price break, manufacturer, and finally stock and delivery time. In the majority of cases, your experience and circuit application will allow you to narrow the options down to a few hundreds. Price and and stock are usually the clincher. Using filtered search is your ally.

I usually wait until I have a larger number of items to purchase in order to avoid paying shipping charges. Then I can easily spend three or more hours making the right selection.
Hi MC,
I do the same as you suggest including the postage part, so it's just how it's done!
C
 

dl324

Joined Mar 30, 2015
12,917
When I looked at my chosen capacitor data sheet, is showed min 4v to maximum 16v.
Can you post a datasheet? I've never seen a minimum required voltage for a capacitor.
I usually leave a margine above any likely voltage I may use, and understand it needs to be higher, but I have never seen a mimimum voltage.
Electrolytic capacitors are rated to withstand their stated operating voltage continuously. They won't tolerate surges above the rated voltage for very long. Cornell Dubilier states the surge rating will be tolerated for 30 seconds at infrequent intervals (at least 5 minutes).

However, I haven't seen surge voltage ratings in any datasheets.
 

BobaMosfet

Joined Jul 1, 2009
1,821
Hi A and B,
When I check capacitors in 'say' Farnell, they only show maximum voltage, say '16v'.
I mainly use 12v, 5, and 3.3v.
When I looked at my chosen capacitor data sheet, is showed min 4v to maximum 16v.
I usually leave a margine above any likely voltage I may use, and understand it needs to be higher, but I have never seen a mimimum voltage.

What I was asking is how do you choose components? Do you always check each component data sheet, before buying, if so it can be time consuming.
Thanks, C
Yes- I always check datasheets- particularly the test values the manufacturer uses- because THOSE are usually the ideal values the manufacturer intends you to use the component at- they don't really guarantee them working close to their maximums.

Usually the most important things are Voltage, Current, and Junction - simultaneously. that means that whatever the maximum junction value is (Watts, or Amps, or Temp), you must keep the other 2 values within the Junction's safe range. Beyond that other things- frequency (if it's a logic gate, does it respond as fast as I need it to?) etc.

You can do thermal calculations to determine how close you can get to the devices 'edge', as well as load-line, q-point, curves, etc.

Tedious? Yes- but that _is_ what engineers do :)
 

Lo_volt

Joined Apr 3, 2014
194
camerart per your datasheet the lowest maximum voltage rated capacitor is 6.3 volts. There is no minimum voltage. If you were using them on a 3.3 volt circuit, you could use capacitors from any of the listed maximum voltage ratings. For your 12 volt circuit, the 16 volt rated part or higher would work. The 6.3 volt and 10 volt rated parts won't work.

Note that for any particular application, you must take into account the ripple that will be present at the capacitor. In one instance, I failed to do so and used a 16 volt part on a 12 volt rail. After a few months the parts started to burn up. It's one of my worst learning experiences as we had to bring in several hundred boards for rework. The 16 volt parts had to be replaced with 25 volt parts.

Package size and cost are generally the reasons to go with the lowest possible voltage rated part. As voltage ratings go up both package size and cost go up as well.
 

Thread Starter

camerart

Joined Feb 25, 2013
2,600
Yes- I always check datasheets- particularly the test values the manufacturer uses- because THOSE are usually the ideal values the manufacturer intends you to use the component at- they don't really guarantee them working close to their maximums.

Usually the most important things are Voltage, Current, and Junction - simultaneously. that means that whatever the maximum junction value is (Watts, or Amps, or Temp), you must keep the other 2 values within the Junction's safe range. Beyond that other things- frequency (if it's a logic gate, does it respond as fast as I need it to?) etc.

You can do thermal calculations to determine how close you can get to the devices 'edge', as well as load-line, q-point, curves, etc.

Tedious? Yes- but that _is_ what engineers do :)
Hi B and LV,
I normally do my amateur best, then if the PCB shows errors, I post them, and hope for advice. Sometimes in my case it's programming, components or poor PCB making.

I 'work' in the morning (mostly) then 'play' in the afternoon. An interesting time for being retired :)
C.
 

Thread Starter

camerart

Joined Feb 25, 2013
2,600
Hi,
It seems to me, that there is a case for a better 'component search engine' to be produced.

EDIT: After the above conversation, I found the caps required, (In my basket) and using the DS above figured out the Footprint on my PCB and changed it. Now they are covering a few tracks, that I'll move to fit them.
Thanks all.
C
 
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