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Use of Aluminum Capacitors

  1. Jun 24, 2012 #1
    Hi guys,

    I am doing a research on the capacitor industry and would like to ask some question.

    I did some basic research online that find out that aluminum capacitors are mainly used in the following areas.

    Power supply output filter
    Blocking and dc-bypass circuits
    Motor start and other non-polarized capacitors
    Audio applications
    Energy discharge capacitors
    Photoflash
    Strobe Applications

    However, I have no clue that products are included in which area. For instance, that products need aluminum capacitors for "power supply output filter"?

    Can someone please give me a few examples in each of the seven areas mentioned above?

    Many thanks in advance!!!
     
  2. jcsd
  3. Jun 24, 2012 #2

    davenn

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    Hi wzheg1837
    welcome to PF :)

    not really sure what other examples you are looking for ?

    you will find aluminium ( electrolytic) capacitors on just about any board of electronics
    Radio, TV, virtually any other domestic and commercial electronics

    The use of Aluminium can capacitors has reduced a bit in recent years as Tantalum caps have become much more popular, specially for low value <100uF and low voltage < ~ 35V applications

    Dave
     
  4. Jun 24, 2012 #3
    Hi Dave,

    Thanks very much for your reply.

    I may not have asked my question clearly...sorry for that.

    For instance, I know that aluminum capacitors are used to "Block dc and bypass circuits". But I don't know which electronic device would need that? Does a computer need to "block dc and bypass circuits" for instance?

    Thanks for your help again. :)
     
  5. Jun 24, 2012 #4

    davenn

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    MOST electrolytic caps, lets say polarised caps, to include both electrolytic and tantalum ones in computers would be for smoothing on DC power supply rails

    You need to realise that aluminium can caps are just a variety of capacitor .. of which there are many .... electrolytic, tantalum, polyester, polystyrene, silver mica, disc ceramic ... just to name a few.
    They ALL can be used for smoothing, blocking and bypassing.
    What you find is different types extend over various value ranges eg electrolytics from ~ 0.1uF to 10's of 1000's of uF (eg 10,000, 47,000uF etc)
    You wont find tantalums with values that high. you also wont find disc ceramics with values that high, tho you will find disc creamics with voltage ratings up to many 1000's of volts.
    Of all those type I listed above, each has its own good and bad points....
    some are very temperature stable, others very low leakage of charge across the dielectric etc

    hope that helps :)

    Dave
     
  6. Jun 24, 2012 #5
    Hi Dave,

    That's been very helpful! Thanks a lot.

    I think I've got a better idea on where I should try to find more info.

    Many thanks again!
     
  7. Jun 24, 2012 #6
    A quick question here if I may.

    I understand that aluminum and tantalum caps are different in many ways, such as size and capacitance.

    What electronic devices use mostly aluminum and what use mostly tantalum caps?
     
  8. Jun 24, 2012 #7

    davenn

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    anywhere that you need large values....
    as I said in an earlier post ... you normally wont find tantalums over ~ 220uF-330uF
    rather electrolytics would be used. this would mainly be in say... power supply smoothing or output stages of audio amplifiers ... the rest of the system may well use mainly tantalums

    Dave
     
  9. Jun 24, 2012 #8
    Yup got it.

    A follow-up, what does "power supply smoothing" mean exatly? Is that the blocking DC and allowing AC thing?
     
  10. Jun 24, 2012 #9
    Hello wzheng, what you are asking seems to be basically the difference between tantalum and aluminium capacitors.

    Firstly tantalums are more expensive than aluminiums for a given capacitance value.
    So other factors being equal aluminium will be used in preference.

    However tantalums have some advantages.
    Tantalums pack a given capacitance into a smaller volume so in these days of miniaturisation the cost penalty is often accepted.
    Tantalums can be placed in a circuit with no DC bias. Aluminium capacitors cannot. This means that for correct operation there has to be a Direct Voltage applied across the (aluminium) capacitor. Aluminium capacitors fail ( and sometimes explode) rather quickly if this voltage is of the wrong polarity.

    There is, however a limit of a few tens of volts that can be applied across a tantalum capacitor so for high Direct Voltage we have to use aluminium.

    Other factors of difference are leakage and distortion.
    Leakage occurs when an undersired current is allowed through the capacitor.
    Distortion occurs when the signal that comes out is not a faithful copy of the signal that went in.
    Tantalum capacitors are superior in both respects so are used in critical situations where one or both are important.
     
  11. Jun 24, 2012 #10
    Hi Studiot:

    Thanks for your reply.

    I start to get a general idea on the differences between aluminum and tantalum caps.

    One question I have (which is actually partially answered by another generous contributor) is the application of both aluminum and tantalum caps.

    I understand that they are both used in almost all electronic devices, but that seems like a pretty big range.

    Could you please help me identify the areas where aluminum caps are mostly used? (e.g. TV? computer? washing machine?) and the areas where tantalum caps are mostly used?

    See, I understand tanta caps have smaller range...but that's a bit difficult for me to grasp as I don't really know what the range of most electronic devices are...

    thanks for help =)
     
  12. Jun 24, 2012 #11

    davenn

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  13. Jun 24, 2012 #12

    davenn

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    there's no fixed rules .... the answers have already really been covered.... size, cost, values, voltage ratings etc etc
    all types of caps can be used in all types of electronics

    Dave
     
    Last edited: Jun 24, 2012
  14. Jun 24, 2012 #13
    Thanks a lot for the explanations!
     
  15. Jun 24, 2012 #14
    You will find aluminium capacitors in parts of a circuit that have a Direct Voltage such as power supply filters and decoupling circuits.
    The job of both power supply capacitors and decoupling capacitors is not to pass a signal but to maintain the DC level of particular point in a circuit.
    Most electronic circuits that have a mains supply have plenty of these. There might be fifty or more decoupling capacitors on a typical computer motherboard plus a few power supply filter capacitors in the computer power supply unit.
    Other equipment with electronic controls will also have these.

    Coupling capacitors on the other hand are there to provide a signal path between two circuit points that are at different voltages. Because they are smaller and and offer less distortion of the signal tantalum capacitors are often used in these positions.
    A typical placement would be in an audio amplifier.
    They might also be found in critical decoupling positions where the leakage loss from an electrolytic would be unacceptable. Again typical of audio amplifier circuitry.

    Aluminium and tantalum capacitors are 'polarised'.
    Other types of capacitor (paper, plastic film, mica etc) are non polarised but only come in lower values of capacitance, but can have a very high voltage rating.

    There are two situations where aluminium and tantalums capacitors cannot be used.

    Firstly the frequency range of use is restricted to audio frequencies and below for polarised capacitors.
    Radio and higher frequencies require low values of capacitance so non polarised types may be used.

    A loudspeaker crossover network (an electronic network that divides the signal in a loudspeaker between tweeter and woofer) is an example of a situation where polarised capacitors will not work. There is no polarising Direct Voltage in the signal amplifier output.
     
  16. Jun 25, 2012 #15

    CWatters

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    Perhaps worth mentioning potential problems with the use of Electrolytic capacitors...

    Their life expectancy is quite temperature sensitive. Standard electrolytic capacitors have a 2,000 hour life at 85C. Now 2,000 hours is only 83 days if used 24 hours a day at that temperature. Fortunately the life expectancy doubles for every 10C reduction in temperature. Even so if you are designing a power supply for a computer or set top box that might get a bit warm you would be wise to use special capacitors rated at 105C and keep them significantly cooler, possibly with a fan. If operated at 65C (105-65=40) they can be expected to last 16 times longer. That way they might even out live the warranty on your product :-)

    This is a very real problem that catches out even well known brands. Not so long ago I had to replace all the capacitors in the power supply of my Sat TV recorder. They had failed in less than two years.

    One place where this is a big potential issue is solar power. Electrolytic capacitors are used in the box of tricks (called an inverter) that turns DC from the solar panels into 230 or 120V AC. Ideally you would like the inverter to last long enough for the system to pay back your investment (eg 10-25 years)! One potential solution being explored is the use of a large number of "micro inverters" instead of one big one. That way each one handles less power and can potentially use a different more reliable type of capacitor.

    http://en.wikipedia.org/wiki/Solar_micro-inverter
     
  17. Jun 25, 2012 #16
    It should perhaps be noted that both aluminium and tantalum capacitors are electrolytic.
     
  18. Jun 26, 2012 #17

    CWatters

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    Oops, yes I tend to forget that. I was referring mainly to aluminium electrolytic caps. Most Tantalum types have much better life expectancy.
     
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