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Hello, varactor(varicap) formula help

michael1978

Mar 17, 2012
388
Joined
Mar 17, 2012
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388
It is common practice for some end-users (or re-sellers) of large quantities of the same part number to test and "bin" all received parts according to the results of the test. With automated test equipment, it is not necessary to just sample a lot of parts to make an accept/reject decision of the whole lot, which was a common procedure in the previous century. While statistically any device from a given production run will have characteristics that fall between the published or "guaranteed" minimum and maximum values, with "most" of the parts having characteristics close to the typical value, the actual range of values depends on how well the production process is understood and controlled.

Unless there are specific quality control documents and specifications that all parts must adhere to, the only remedy an end-user has is to return to the manufacturer or the re-seller any parts that do not fall within the limits of the guaranteed values. Some purchase orders may specify that an entire lot will be returned if any of the parts fails to meet specifications. Obviously such practices will inflate the cost of the part. If the end-user has a very large volume commitment, they may bin the parts after testing and sell the outliers at a discount, reserving for themselves those bins closest to the "nominal" value. These practices clearly put the hobbyist buying in onesie-twosie quantities at a disadvantage, but there is little that can be done about it. The Golden Rule applies: He who has the Gold, Rules.


Somewhat disgusted, not mad, that you have failed to understand. Where did you find the value of 6.8 pF? What do you mean to "divide 6.8 pf with 2V and 20V? If you are going to divide anything, pick any number between the minimum capacitance ratio of 5.0 and the maximum capacitance ratio of 6.5 and divide that capacitance ratio number into any value between the minimum and maximum capacitance values that occur with 2 V reverse bias. This range of values represents the maximum varactor capacitance. The result after dividing by the capacitance ratio will be the minimum varactor capacitance.

The minimum varactor capacitance occurs with 20 V DC reverse bias. The maximum varactor capacitance occurs with 2 V DC reverse bias. The varactor will have more capacitance for reverse bias voltages less than 2 V, but the capacitance is not specified nor is it guaranteed. The varactor will have less capacitance for reverse bias voltage more than 20 V, but the capacitance in not specified nor is it guaranteed. Exceeding 25 V reverse bias may irrevocably damage the varactor. It is inadvisable to forward-bias the varactor diode without providing a means to limit the forward current, but it is your part, you own it: do what whatever you feel is necessary to advance your learning process.
THANK YOU A LOTTTTTTTTTTTT...........for helping ;-)
 

hevans1944

Hop - AC8NS
Jun 21, 2012
4,891
Joined
Jun 21, 2012
Messages
4,891
Why do you want to try measuring such a tiny amount of capacitance? It is 0.00000000001 micro-farads.
I think you might want to check your decimal points. We are discussing capacitance on the order of ten picofarads. 0.00000000001 micro-farads is 10 pico-micro-farads (pmfd), a million times smaller than ten micro-microfarad (mmfd), which is a very small capacitance indeed.

OTOH, 10 picofarads is 0.00000000001 farads or 10 micro-micro-farads (mmfd), which is still pretty damned small.

It is for this reason (probably) that God invented microwaves and requires us to use waveguides and Smith charts and microwave strip-line techniques for tuning purposes instead of discrete inductors and capacitors. James Clerk Maxwell worked all this out ages ago during a direct communication from God. Sort of like Moses and the Ten Commandments, Maxwell and the Four Equations explains everything. Some study required.

Here on EP there are just too many damn zeroes to keep things straight and in perspective, unless you can figure out how to express numbers in this forum using scientific notation: 0.00000000001 = 1 x 10^(-11) = 10 x 10^(-12) = 10 pico-somethings. OK, I suppose you could import exponential or super-scripted characters as images placed in-line with text, but that seems to be an awful lot of trouble. Maybe we should just compose text using a real text editor and upload or attach it as a PDF file. Nah, bad idea. That would really mess up the continuity of the threads. I have to open a separate app to read it, every time someone posts a PDF, which can be a real PITA.

@Ian: hows come we can't insert sub-script and super-script characters using the on-line rich text editor?
 
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