What is a Vericap Diode ? - Electronic Circuits Projects Diagrams Free

Ravi · 24th May 2003, 03:47 AM

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 · 24th May 2003, 05:27 AM

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

**kinjalgp** · 24th May 2003, 05:53 AM

Quote:

often used in AM radios

It is often used in FM radios. Not in AM

Phasor · 24th May 2003, 06:01 AM

oops

ops: I couldn't quite remember - took a stab in the dark...

Sebi · 24th May 2003, 07:20 AM

Also used in AM radiotuners e.g .:BB113 5....120pF

Dean Huster · 24th May 2003, 11:57 AM

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 · 26th May 2003, 01:52 AM

Thanks everybody for valuable information.

Ravi

pebe · 26th May 2003, 08:25 PM

Quote:

Originally Posted by kinjalgp

Quote:

often used in AM radios

It is often used in FM radios. Not in AM

It can be found in AM radios. It's only frequency aware - not modulation type.

**kinjalgp** · 27th May 2003, 05:12 AM

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 · 28th May 2003, 04:00 PM

Quote:

Originally Posted by kinjalgp

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** · 28th May 2003, 05:55 PM

I see. So you were talking about voltage controlled digital tuning.

pebe · 28th May 2003, 06:49 PM

Quote:

Originally Posted by kinjalgp

I see. So you were talking about voltage controlled digital tuning.

Yes, or it could be analogue - controlled by a pot.

**kinjalgp** · 28th May 2003, 08:07 PM

Thanks

**mechie** · 29th May 2003, 08:40 AM

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).

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

24th May 2003, 03:47 AM	(permalink)
Ravi	What is a Vericap Diode ? 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 :?

24th May 2003, 05:27 AM	(permalink)
Phasor	A varicap diode, is a diode which has a characteristic of decreasing its capacitance, as the reverse voltage increases. Often used in AM radios.

24th May 2003, 06:01 AM	(permalink)
Phasor	oops ops: I couldn't quite remember - took a stab in the dark...

24th May 2003, 07:20 AM	(permalink)
Sebi	Also used in AM radiotuners e.g .:BB113 5....120pF

24th May 2003, 11:57 AM	(permalink)
Dean Huster	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 __________________ Dean Huster, Electronics Curmudgeon Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines). R.I.P.

26th May 2003, 01:52 AM	(permalink)
Ravi	Thanks Thanks everybody for valuable information. Ravi

27th May 2003, 05:12 AM	(permalink)
kinjalgp	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 __________________ "There is no way to peace, peace is the way!"

28th May 2003, 05:55 PM	(permalink)
kinjalgp	I see. So you were talking about voltage controlled digital tuning. __________________ "There is no way to peace, peace is the way!"

28th May 2003, 08:07 PM	(permalink)
kinjalgp	Thanks __________________ "There is no way to peace, peace is the way!"

29th May 2003, 08:40 AM	(permalink)
mechie	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). __________________ I need a memory upgrade ... My head is full !