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What is a Vericap Diode ?

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Ravi

Member
Dear All,

Whilst I was going through some ckts, I came across a Vericap diode. I do not understand this. Is it similar to any other diode or is the mecanisum is different? Why a vericap is necessary. Appreciate your help.

Ravi :?
 

Phasor

Member
A varicap diode, is a diode which has a characteristic of decreasing its capacitance, as the reverse voltage increases. Often used in AM radios.
 

Dean Huster

Well-Known Member
Varicaps

Most low-leakage silicon diodes can be used as variable capacitance diodes when used in the reverse direction ("Varicap" is actually a tradename similar to "HexFET"), although your run-of-the-mill silicon swithing diode has a smaller capacitance and small capacitance change. "Varicaps" are bred for larger capacitances and capacitance changes and are available in a variety of different characteristics. Another popular series of "Varicaps" are the "MVxxxx" series of type numbers.

Dean
 

Ravi

Member
Thanks

Thanks everybody for valuable information.

Ravi
 

kinjalgp

Active Member
Oops sorry! :( But I have never seen a varicap in AM receiver.

Frequency in AM is constant and therefore if a varicap diode is used in AM receiver, it will just act as a constant value capacitor for a chosen carrier which means there is no point in using a varicap. A constant value capacitor can also be used in its place.
Whereas in FM, frequency is releted to modulating signal and so any change in frequncy will affect the capacitance of varicap which can be used to demodulate the FM signal.

Well, this is what I am thinking, but there may be AM circuits which uses this diode. IF anyone has one, I would like to see it.
Thanks :)
 

pebe

Member
kinjalgp said:
Oops sorry! :( But I have never seen a varicap in AM receiver.

Frequency in AM is constant and therefore if a varicap diode is used in AM receiver, it will just act as a constant value capacitor for a chosen carrier which means there is no point in using a varicap. A constant value capacitor can also be used in its place.
Whereas in FM, frequency is releted to modulating signal and so any change in frequncy will affect the capacitance of varicap which can be used to demodulate the FM signal.

Well, this is what I am thinking, but there may be AM circuits which uses this diode. IF anyone has one, I would like to see it.
Thanks :)
Yes, the carrier frequency of any ONE AM station is constant - as distinct from FM where it varies.

But you need to tune to more than one station and that means varying the local osc frequency. Either by using a variable capacitor altered by a knob, or by varying the volts on a varicap if it is a digital tuner
 

kinjalgp

Active Member
I see. So you were talking about voltage controlled digital tuning. :)
 

mechie

New Member
Audio Varicaps?

I'm sure I remember a circuit for an analogue synthesiser's voltage controlled filter using a "real" varicap, I know I have diagrams using signal diodes in a ladder network as "cheapo" varicaps - same theory (as Dean said way back in this thread).
 
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