Copyright: 1996 - 2024
BSEE - KB3UON
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling
2 MB. Its primary purpose was to provide me with ready access to commonly needed
formulas and reference material while performing my work as an RF system and circuit
design engineer. The World Wide Web (Internet) was largely an unknown entity at
the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps
while tying up your telephone line, and a nice lady's voice announced "You've Got
Mail" when a new message arrived...
All trademarks, copyrights, patents, and other rights of ownership to images
and text used on the RF Cafe website are hereby acknowledged.
My Hobby Website:
OP amp design - RF Cafe Forums
RF Cafe Forums closed its virtual doors in 2012 mainly due to other social media
platforms dominating public commenting venues. RF Cafe Forums began sometime around
August of 2003 and was quite well-attended for many years. By 2010, Facebook and
Twitter were overwhelmingly dominating online personal interaction, and RF Cafe
Forums activity dropped off precipitously. If the folks at
phpBB would release a version with integrated
sign-in from the major social media platforms, I would resurrect the RF Cafe Forums,
but until then it is probably not worth the effort. Regardless, there are still
lots of great posts in the archive that ware worth looking at.
Below are the old forum threads, including responses to the original posts.
|-- Amateur Radio
Gripes & Humor
-- CAE, CAD, &
Test & Measurement
Post subject: OP amp design Posted: Sun Sep 18, 2005 10:59
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 ?
you in advance.
Post subject: Posted:
Sun Sep 18, 2005 11:10 am
Sorry for the small image.
Here I make
it bigger. Thanks.
OpAmp QuestionPosted: Mon Sep 19, 2005 11:53 am
It's a matter of
Resistors convert power=current*voltage into heat, capacitors
Why waste power?
Post subject: Re: OpAmp QuestionPosted: Mon Sep 26, 2005
It's a matter of numbers.
convert power=current*voltage into heat, capacitors don't.
removes any DC offsets from the generator and the 500k provides the
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