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OP Amp Design - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement

Post subject: OP amp design Posted: Sun Sep 18, 2005 10:59 am
Hi everyone,

I am going to design a zero crossing detector with using an op amp.
Then, I found a basic circuit from internet that the circuit uses voltage divider from the main source (230 V) as as input voltage (V+) for the op amp.

One thing that I am not sure is, why it uses coupling capacitor instead of resistor in the voltage divider ? What is the advantage of it ?

Ok. Thank you in advance.


Post subject: Posted: Sun Sep 18, 2005 11:10 am
Sorry for the small image.
Here I make it bigger. Thanks.


Post subject: OpAmp QuestionPosted: Mon Sep 19, 2005 11:53 am
It's a matter of numbers.

Resistors convert power=current*voltage into heat, capacitors don't.

Why waste power?

Good Luck!


Post subject: Re: OpAmp QuestionPosted: Mon Sep 26, 2005 11:25 am
Guest wrote:
It's a matter of numbers.

Resistors convert power=current*voltage into heat, capacitors don't.

Why waste power?

Good Luck!

Good Try..

The capacitor removes any DC offsets from the generator and the 500k provides the ground reference.


Post subject: Coupling capacitorPosted: Wed Sep 28, 2005 5:44 pm
In most areas, the 230 V mains voltage comes from a transformer. Since transformers do not pass DC, there should be *NO* DC offsets on the incoming voltage.

A resistor would, in fact, work in the circuit where the capacitor is shown.

Good Luck!

Posted  11/12/2012

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