Variable capacitor circuits - Page 4 - Electronic Circuits Projects Diagrams Free

walters · 19th January 2006, 04:16 AM

Are Varactors a reversed bias Zenor diode or a regular diode?

walters · 19th January 2006, 04:55 AM

varactor diodes the capacitances are in the picofarads

Can i use Varactors in "series" to increase the capacitances?

Or i would need a "Custom" Varactor diode to have the capacitance in the microfarads?

What would the Varactors doping process do different and how? the PN junction needs to be Bigger?

I need a Varactor is the Mircofarads? which ones is there please?

akg · 19th January 2006, 05:49 AM

Quote:

Originally Posted by walters

varactor diodes the capacitances are in the picofarads

Can i use Varactors in "series" to increase the capacitances?

Or i would need a "Custom" Varactor diode to have the capacitance in the microfarads?

What would the Varactors doping process do different and how? the PN junction needs to be Bigger?

I need a Varactor is the Mircofarads? which ones is there please?

varactors a reverse biased diodes with specific dopping to act it as 'varactor' .
and u cannot (practicaly)get a uF varactor.
hava a look at
http://en.wikipedia.org/wiki/Varactor
http://www.vias.org/simulations/simusoft_varactor.html
http://www.play-hookey.com/semicondu...ed_diodes.html

walters · 19th January 2006, 05:54 AM

thanks for the help

How can i get a a uF varactor?

I need uf Varactors?

How can i make one or put them in series or so to make a uf varactor?

akg · 19th January 2006, 06:26 AM

Quote:

Originally Posted by walters

thanks for the help

How can i get a a uF varactor?

I need uf Varactors?

How can i make one or put them in series or so to make a uf varactor?

u cannot (practicaly)get a uF varactor. afaik

walters · 19th January 2006, 06:28 AM

why not?

akg · 19th January 2006, 06:31 AM

Quote:

Originally Posted by walters

why not?

it requires a large depletion layer region (large area).
Also varacters are used in HF/UHF ckts for tuning , that reqs only pf variation
i hope u have visted the links i suggested.

walters · 19th January 2006, 06:37 AM

So i have to get this Custom made to have a large depletion layer region (large area)?

akg · 19th January 2006, 06:40 AM

Quote:

Originally Posted by walters

So i have to get this Custom made to have a large depletion layer region (large area)?

AFAIK

walters · 19th January 2006, 06:42 AM

A large depletion layer region large area would give me more capacitance to be mircofarads?

Most Varactors are used:
tunable filters and oscillators , frequency multiplication and frequency mixing

akg · 19th January 2006, 07:12 AM

Quote:

Originally Posted by walters

A large depletion layer region large area would give me more capacitance to be mircofarads?

Most Varactors are used:
tunable filters and oscillators , frequency multiplication and frequency mixing

walters
u have a 1000 1PF capacitors , how would u make a 1uF capacitor out of it?

walters · 19th January 2006, 07:16 AM

put another one in series? or 3 or 5 in series? to ADD them?

akg · 19th January 2006, 07:22 AM

Quote:

Originally Posted by walters

put another one in series? or 3 or 5 in series? to ADD them?

if u have got some capacitor and a measurement eqp: , try it out and check what happens.

walters · 19th January 2006, 07:24 AM

Yea but i still can't Vary the Varactors in Mircofarads i need to have a variable .01uf or .47 or 220uf Varactors i wish they made these

I need to use the .01uf Varactors in a phase shift network filter for audio not radio

akg · 19th January 2006, 07:40 AM

Quote:

Originally Posted by walters

Yea but i still can't Vary the Varactors in Mircofarads i need to have a variable .01uf or .47 or 220uf Varactors i wish they made these

I need to use the .01uf Varactors in a phase shift network filter for audio not radio

audioguru wrote :

Quote:

A 0.22uF capacitor's effective value in a filter circuit can be changed with PWM. With 100% duty-cycle it is 0.22uF. With 10% duty-cycle it is 0.022uF. With 1% duty-cycle it is ..., you figure it out. Of course, the frequency of the PWM is very high so can't be heard.

Repeat

Quote:

You also didn't hear me describe how PWM can vary the capacitance over a wide range of any capacitor. I've used switched-capacitor lowpass filter ICs for years. They switch internal capacitors similar to PWM and work perfectly.

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

19th January 2006, 04:16 AM	(permalink)
walters	Are Varactors a reversed bias Zenor diode or a regular diode?

19th January 2006, 04:55 AM	(permalink)
walters	varactor diodes the capacitances are in the picofarads Can i use Varactors in "series" to increase the capacitances? Or i would need a "Custom" Varactor diode to have the capacitance in the microfarads? What would the Varactors doping process do different and how? the PN junction needs to be Bigger? I need a Varactor is the Mircofarads? which ones is there please?

19th January 2006, 05:54 AM	(permalink)
walters	thanks for the help How can i get a a uF varactor? I need uf Varactors? How can i make one or put them in series or so to make a uf varactor?

19th January 2006, 06:37 AM	(permalink)
walters	So i have to get this Custom made to have a large depletion layer region (large area)?

19th January 2006, 06:42 AM	(permalink)
walters	A large depletion layer region large area would give me more capacitance to be mircofarads? Most Varactors are used: tunable filters and oscillators , frequency multiplication and frequency mixing

19th January 2006, 07:16 AM	(permalink)
walters	put another one in series? or 3 or 5 in series? to ADD them?

19th January 2006, 07:24 AM	(permalink)
walters	Yea but i still can't Vary the Varactors in Mircofarads i need to have a variable .01uf or .47 or 220uf Varactors i wish they made these I need to use the .01uf Varactors in a phase shift network filter for audio not radio