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I have read that varicaps (capacity diodes) are a "modern" alternative to variable capacitors. In several electronics books only positive properties of varicaps are mentioned.

But several major distributors (here in Germany) simply don't offer varicaps, or just have less than 5 of SOT-23 models. (For comparison: same distributor offers around 1000 different diode models.)

At three largest German distributors of electronic components I couldn't find a single DO-xxx case varicap. Only SOT-xxx.

Does it mean that varicaps are obsolete? If so, what do people use in today's circuits as "replacement"? Or, more general, is there some more common "concept" to vary capacity?

Thank you.

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Digi-Key lists 946 items under "variable capacitance diodes", including 302 parts from Infineon or NXP. If you can't get these parts from a German distributor, something is very wrong. –  The Photon Feb 27 '12 at 2:43
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5 Answers 5

They are still widely used in VCOs in phase-locked loop frequency synthesisers.

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There are many devices that exist that have niche use. PLLs are extremely common and it would blow your mind how often you have varicaps in something.! –  Kortuk Apr 10 '10 at 9:46
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Farnell show 40 lines, including a D0-35 package.

I think reports of their death are greatly exaggerated :-)

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Try exploring some ham radio DIY sites. I was looking for DIY receiver designs last month, and varactors (as we call 'em over here) are used commonly. Sorry, I took no detailed notes on this. Sites with varactor-based projects will probably have information on suppliers, or at least have a forum for asking.

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I just wanted to note that varicaps are not an "alternative" to variable capacitors:

  1. Your typical variable capacitors require the user to turn a screwdriver and are still used in trimming HF filters.

  2. Varicaps OTOH change capacitance as a function of reverse DC voltage so they are electronically adjustable.

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On a Dutch forum roughly this question was asked recently (http://www.circuitsonline.net/forum/view/102189/1/varicap). The anwsers amount to:

  • yes, through-hole varicaps are becoming hard to get
  • why don't you switch to SMD?
  • try a 1N400x! much cheaper, and guaranteed to be available in the future
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Implied, but not said: Normal diodes also exhibit this characteristic. –  gbarry Jul 16 '12 at 18:53
    
Nice link, but, uh, not in my language :) –  gbarry Jul 16 '12 at 18:54
    
That's why I included the mangament summray here. I left it for the intelligent reader to conclude, but yes: all diodes have varicap behaviour, and the 'base' capacity is more-or-less releated to the current capacity (or rather, the P/N area), so a 1N400x makes a mabe not ideal but certainly cheap and readily available alternative. –  Wouter van Ooijen Jul 16 '12 at 19:26
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