
Home  Forums  Rules  Articles  diyAudio Store  Gallery  Wiki  Blogs  Register  Donations  FAQ  Calendar  Search  Today's Posts  Mark Forums Read  Search 
Construction Tips Construction techniques and tips 

Please consider donating to help us continue to serve you.
Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving 

Thread Tools  Search this Thread 
10th September 2010, 12:30 PM  #1 
diyAudio Member

Resonant circuit design?
I wasn't sure which area this question belongs so I guess this one is as good as any...
When designing a capacitive resonant circuit using the formula f=1/2*pi*R*C does it matter about the relative impedances of the resistors and capacitors? I mean, as long as the combination arrives at the resonant frequency you choose, can you just put any combination of resistor and capacitor you want?
__________________
Any technology sufficiently advanced is indistinguishable from magic 
10th September 2010, 12:51 PM  #2 
diyAudio Moderator

There's a bit more to it than that... not least the practicalities and properties of real world components.
Look up "Q" with regard to resonance... it's a measure of the "goodness" of a resonant circuit and is affected by real world properties of components. To answer the question, yes, if the impedance of a cap deviates from the ideal then it affects the resonant circuit. This is particularly true of coils as well. The formula doesn't take these into consideration, it assumes ideal.
__________________
 Installing and using LTspice IV. From beginner to advanced. 
10th September 2010, 01:45 PM  #3 
diyAudio Member
Join Date: May 2007

RC is not a resonant circuit, you need LC or an active circuit for resonance. The value given by the RC formula is a corner frequency, not a resonance.
The impedances will give the stated frequency whatever their individual values  but you have to realise that the resistance/capacitance which appears in the formula is not the value of a component which you have just soldered in, but the effective value after the loading of the rest of the circuit is considered. People often forget this. 
10th September 2010, 06:05 PM  #4 
Banned


10th September 2010, 08:03 PM  #5 
diyAudio Member

Ok, I see that a picture is worth a thousand words. In the attachment, if I just change the capacitors by an order of magnitude, will I get approximately an order of magnitude change in the oscillation frequency?
This was taken from Linear Technology's app note AN67.
__________________
Any technology sufficiently advanced is indistinguishable from magic 
10th September 2010, 09:16 PM  #6 
diyAudio Member
Join Date: May 2007

Yes, because they are already significantly larger than any likely circuit stray capacitances. However, if you dropped them by a factor of 100 then the frequency might not change by quite that much as a few hundred pF is starting to get near stray values.

10th September 2010, 09:19 PM  #7  
diyAudio Member
Join Date: Sep 2006

Quote:
If it's the latest LTCxxx or ADzzz, your chances are better. 

Thread Tools  Search this Thread 


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
connex electronics A350 SMPS halfbridge resonant design  Artcore87  Swap Meet  0  8th September 2010 12:33 AM 
Resonant chambers in a TL design? MJK, or any other officiando...ANy input?  mondogenerator  MultiWay  20  25th October 2009 01:16 PM 
Help me out with a circuit design  Daddy Rocket  Tubes / Valves  10  16th December 2007 04:53 AM 
Design of Resonant Input Choke PSU  Yugo  Tubes / Valves  29  21st April 2007 12:25 AM 
need help on circuit design  bakashijinsan  Chip Amps  0  11th February 2004 10:31 AM 
New To Site?  Need Help? 