hello I'm from the HF (High Freq.) and microwave community. My rough estimate for coupling capacitors is: impedance of the coupling cap should be about 1/10 of the characteristic impedance (more acurately spoken: reactance) at the lowest frequency to have neglectible losses.
Your case: what capacitor has a reactance of 50 Ohms (1/10 of 500) at 40 kHz? X_c = 1/(2*pi*f*C) ==> C = 1/(2*pi*f*X_c) (units Hz, Ohms, Farads) C = 1/(6.283*40000*50) F = 79.6e-9 F = 79.6 nF = 0.0796 uF rounded to next practical value: ==> 0.1 uF (or 0.22 uF) attention: such large cap. values as SMDs are ceramic caps made of material with high dieelectric constant. X7R ceramics is in most cases ok (0.1uF 50V available in size 0805); Z5U or Y5V change their capacitance value over temperature and with applied (DC) voltage, in worst case more than 50% of the value at 25 deg C. Best (highest stability, highest Q, lowest resistive losses) is NP0 or C0G ceramics (maybe max 10nF available in size 1206 with 50V), and at low frequs (Audio Freq) some foil caps. hope this helps regards Alois > First engineers aproach is calculate (go and study electronics), if that fails > ask yourself what could go wrong using the try and error method, if there > isn't much what could go wrong, get yourself some parts and try. > > Paul, on need more information to be able to answer this, > whats the frecuency, is it continous or pulsed operation, what are the > impedances, > etc. we can't really discuss this by e-mail. > > Or I am wrong ? > > Friedel > > > On 6 Dec 2004 at 3:15, Paulo Castro wrote: > > > > > Hello ListMembers, > > I have a very off-topic subject, maybe the correct destination is [EE]. I > > hope You > could bring some > > light on this. > > The question is: How can I determine the value of a capacitor between > > amplifier > stages, or > > between a transdutor and an operational amplifier? Of course, the capacitor > > would > permit only the > > AC component of the output of the transducer to be amplified, but what > > should be > the best value? > > In the case of the transdutor, its resistance is about 500 ohms, and the > > center > frequency is 40 > > KHz. > > > > Best regards, > > > > Paul > > > > > > Yahoo! Mail - Agora com 250MB de espa�o gratuito. Abra uma conta agora! > > > Friedel Bruening > Bolivian Instruments > Casilla 4856 > Santa Cruz > Bolivia > Mobile : ++591-773-92119 > Tel/Fax : ++591-3-3580572 > e-mail : [EMAIL PROTECTED] > -- > Author: Friedel Bruening > INET: [EMAIL PROTECTED] > > Fat City Hosting, San Diego, California -- http://www.fatcity.com > --------------------------------------------------------------------- > To REMOVE yourself from this mailing list, send an E-Mail message > to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in > the message BODY, include a line containing: UNSUB CHIPDIR-L > (or the name of mailing list you want to be removed from). You may > also send the HELP command for other information (like subscribing). - - - - - - - - - - - - - - - - - - - - - - - - - - Alois Bauer WORK Microwave GmbH Raiffeisenstr. 12, D-83607 Holzkirchen, Germany Tel. {+49} (0)8024-6408-0 / FAX (0)8024-640840 -- Author: Alois Bauer INET: [EMAIL PROTECTED] Fat City Hosting, San Diego, California -- http://www.fatcity.com --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB CHIPDIR-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
