Re: [OT] Capacitor value

[Fred Townsend]

Paulo this is the type question I love to teach in an advanced circuits class because the freshman student is likely to give a very different answer than the experienced engineer. Your specifications are a minefield of problems. First: You stated your CENTER frequency is 40 KHz.  Capacitors for this type application are selected by the MINIMUM frequency therefore the lower frequency or bandwidth of the transducer is required. Second: There are many types of capacitors. Capacitors are NOT ideal components. What is the value of the DC voltage you are trying to block? This will determine the working voltage rating of your capacitor. Also what is your tolerance to leakage. Some types of capacitors have relatively high values of leakage. Third: What is the nature of the transducer? Is it a wound component? If so it will have a relatively high value of inductance.  The inductance will resonate with the coupling capacitor. Granted with 500 ohms resistance the Q, figure of merit, will be low.  This means the resonate effects will not dominate unless you have some critical flatness or ripple requirements. All things said I think you have over simplified your question. It is critical to know the nature of the application even if you can't supply all the missing parameters. Please resubmit you question. Fred Townsend 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 espaço gratuito. Abra uma conta agora!