Basics, Component specification / Selection

• Basics, Component specification / Selection
  Posted by jgbena on 27 Jan, 2012 22:08
• When designing your own circuits and you need a capacitor, just how do you go about selecting the right one.  Obviously you can calculate what value you need and all but what tells you which tyle to use in your project?  there are many different kinds.  When do you use a ceramic vs. a an electrolytic, or a tantalum, or mica etc..  are there some general guidelines?
• #1 Reply
  Posted by Rerouter on 27 Jan, 2012 23:00
• Generally it comes down to the charichteristics of each type, and dave has done a full video on this,
  
  http://www.eevblog.com/2009/09/26/eevblog-33-1of2-capacitor-tutorial-electrolytic-tantalum-and-plastic-film/
  http://www.eevblog.com/2009/09/26/eevblog-33-2of2-capacitor-tutorial-ceramics-and-impedance/
  
  in short, ceramics have a very low ESR, but also have lower capacity,
  tantalums have moderatly low ESR, but have capacities upto a few hundred uF
  and electros, they have sometimes adhorrent ESR and will dry out in about 20 years, but can have capacities upto Farads,
• #2 Reply
  Posted by IanB on 27 Jan, 2012 23:19
• Yup. Some capacitors are used in circuits as reservoirs for storing and releasing energy, some capacitors are for blocking DC while passing AC, some capacitors are for bypassing AC to ground, some capacitors are used as timing devices, and some are for two or more of these at the same time. Once you identify what your capacitor is being used for, it helps to narrow the selection of which type to use.
• #3 Reply
  Posted by Psi on 28 Jan, 2012 00:13
• It's not so bad now that there's polymer electrolytics with decent ESR.
  The computer motherboard manufactures are responsible for bringing them to market at a good price.
  
  Now ya can get a 6-16V 1500uF electrolytic caps with 6A ripple current which make awesome DC/DC powersupplies without needing to spend mega $ on a large array of ceramic or tantalum caps.
• #4 Reply
  Posted by vk6zgo on 28 Jan, 2012 01:34
• Cheat!! Look at what other people have used.
  There are always projects in Electronics mags & on websites.Some articles actually spend time explaining why they chose particular components.
  If you can,look at real,commercially made Electronic equipment.
  After a while,you will get a "feel" for the standard  component types used in particular sorts of circuits.
  Your design may not be like any of them,but you will recognise similar situations,& be guided by them.
  
  It seems many people feel this is "copying" & would rather rely on their own ,sometimes immature design skills,with the result being a good idea,but spoilt by poor choice of components.
  
  VK6ZGO
• #5 Reply
  Posted by olsenn on 28 Jan, 2012 03:42
• Absolutely; this is something that you won't really be able to nail down until you get lots of experience with it. In practice it is largely trial and error until you get used to the shortcommings of each capacitor type (the hard way).
  
  Here's a quick, non-exhaustive guide coutesy of "The Art of Electronics - 2e"
  
  
  
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• #6 Reply
  Posted by jgbena on 29 Jan, 2012 01:18
• WoW!  Thanks for the great replies.
  
  And I though I have crawled through all of Dave's videos.. I must have missed those, Ill go look them up as soon as I can.  and @olsenn, I just ordered that book from amazon and am axiously awaiting its arrival. 
  
  Thanks again all.
  
  Jon