Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
That doesn't sound right.I'm aware of uA741 slew rate issues and limited GBW, but I can't even
get above gain of 2x with Vcc of +/- 12v and input sine wave of 5mV
peak at only 100Hz (yup, one hundred Hz). What?
Are you applying any feedback? It sounds like you are trying to operate itI'm aware of uA741 slew rate issues and limited GBW, but I can't even
get above gain of 2x with Vcc of +/- 12v and input sine wave of 5mV
peak at only 100Hz (yup, one hundred Hz). What?
At 100 Hz the open loop gain should be about 100 times and, 5mV should
give
about 500mV out, open loop.
Connect the amp as a gain of 10 with a 1k input resistor and a 10k
feedback
resistor to the neg input, ground the pos input and be sure there is a DC
path to ground through your source and try again.
Your right....I had a brain-fart and figured it wrong. For some reason I"Bob is too Eld"
At 100 Hz the open loop gain should be about 100 times and, 5mV should
give
about 500mV out, open loop.
** Err - the open loop gain of a 741 is 10,000 times at 100Hz.
Connect the amp as a gain of 10 with a 1k input resistor and a 10k
feedback
resistor to the neg input, ground the pos input and be sure there is a
DC
path to ground through your source and try again.
** No need for a DC path exists when the pos input is grounded cos the
feedback loop will make sure the neg input is within 1 mV of the pos one.
... Phil
"Phil Allison"
"Bob is too Eld"
At 100 Hz the open loop gain should be about 100 times and, 5mV should
give about 500mV out, open loop.
** Err - the open loop gain of a 741 is 10,000 times at 100Hz.
Connect the amp as a gain of 10 with a 1k input resistor and a 10k
feedback resistor to the neg input, ground the pos input and be sure
there is a DC path to ground through your source and try again.
** No need for a DC path exists when the pos input is grounded cos the
feedback loop will make sure the neg input is within 1 mV of the pos one.
Your right....I had a brain-fart and figured it wrong. For some reason I
can't seem to divide a million by 100. Oh well, the fact remains that the
OP must be trying to run the amp open loop.
I'm aware of uA741 slew rate issues and limited GBW, but I can't even
get above gain of 2x with Vcc of +/- 12v and input sine wave of 5mV
peak at only 100Hz (yup, one hundred Hz). What?
It would be nice if you can show us your attempted circuit?
Open loop gain of a 741 would give you a rail to rail square wave onI'm aware of uA741 slew rate issues and limited GBW, but I can't even
get above gain of 2x with Vcc of +/- 12v and input sine wave of 5mV
peak at only 100Hz (yup, one hundred Hz). What?
in an open loop is what you're trying to convey in this situation.On Fri, 16 Oct 2009 18:02:16 -0700 (PDT), cc <pccmd@comcast.net
wrote:
I'm aware of uA741 slew rate issues and limited GBW, but I can't even
get above gain of 2x with Vcc of +/- 12v and input sine wave of 5mV
peak at only 100Hz (yup, one hundred Hz). What?
Open loop gain of a 741 would give you a rail to rail square wave on
the output. You have to be limiting the gain external to the op amp
or your measuring method or instrument is wrong.
A 741 won't do Rail TO Rail. I think the fact it does square wave
"cc" <pc...@comcast.net> wrote in message
news:37514530-3118-4123-bc52-ff93af7461f1@i12g2000prg.googlegroups.com...
I'm aware of uA741 slew rate issues and limited GBW, but I can't even
get above gain of 2x with Vcc of +/- 12v and input sine wave of 5mV
peak at only 100Hz (yup, one hundred Hz). What?
Are you applying any feedback? It sounds like you are trying to operate it
open loop.
At 100 Hz the open loop gain should be about 100 times and, 5mV should give
about 500mV out, open loop.
However, the DC input offset voltage and offset current could easily drive
the open loop amp output into one of its rails causing virtually no AC out.
Connect the amp as a gain of 10 with a 1k input resistor and a 10k feedback
resistor to the neg input, ground the pos input and be sure there is a DC
path to ground through your source and try again.
On Oct 16, 7:57 pm, "Bob Eld" <nsmontas...@yahoo.com> wrote:
"cc" <pc...@comcast.net> wrote in message
news:37514530-3118-4123-bc52-ff93af7461f1@i12g2000prg.googlegroups.com....
I'm aware of uA741 slew rate issues and limited GBW, but I can't even
get above gain of 2x with Vcc of +/- 12v and input sine wave of 5mV
peak at only 100Hz (yup, one hundred Hz). What?
Are you applying any feedback? It sounds like you are trying to operate it
open loop.
At 100 Hz the open loop gain should be about 100 times and, 5mV should give
about 500mV out, open loop.
However, the DC input offset voltage and offset current could easily drive
the open loop amp output into one of its rails causing virtually no AC out.
Connect the amp as a gain of 10 with a 1k input resistor and a 10k feedback
resistor to the neg input, ground the pos input and be sure there is a DC
path to ground through your source and try again.
Thank you all.
It's set up as simple inverter, with (+) pin to ground via same R as
the input R and only 100Hz.
Still working on it, but I replaced the F/B circuit with only 10ohms
(R) between signal and (-) pin, and 1000k between (-) pin and output,
for closed loop gain 100x and it worked. So it seems that I need low
R at (-) input terminal. You see, I had been using R=1k and the
feedback R=100k.
Now, my fcn generator has about 700 o/p impedance. Does that matter?
I had similar problem with AD8620 and CA3140...still working on them.
On Oct 16, 6:02 pm, cc <pc...@comcast.net> wrote:
I'm aware of uA741 slew rate issues and limited GBW, but I can't even
get above gain of 2x with Vcc of +/- 12v and input sine wave of 5mV
peak at only 100Hz (yup, one hundred Hz). What?
OK, guys.....my bad.............
I thought I had checked this first when I began using my (cheapo) fcn.
generator, but I was getting about 2.5v dc bias on which I was riding
2-5mv signal, so of course i couldn't get much gain with the +/- 12v
supply(or 9 depending on my mood that day). All I got was flatline
or noise when trying for even 10x gain.
Sorry for the fuss, but I'm learning at home.....I'm lucky I found a
deal on an old Tek 7633 and I can even see the waveforms at all. This
is how we learn.......sometimes with help from others.
Lesson, check all the supposedly obvious solutions first.
CC
Have you seen that magical smoke yet?
OK, guys.....my bad.............I'm aware of uA741 slew rate issues and limited GBW, but I can't even
get above gain of 2x with Vcc of +/- 12v and input sine wave of 5mV
peak at only 100Hz (yup, one hundred Hz). What?
specifications at the rail extremes.default wrote:
On Fri, 16 Oct 2009 18:02:16 -0700 (PDT), cc <pccmd@comcast.net
wrote:
I'm aware of uA741 slew rate issues and limited GBW, but I can't even
get above gain of 2x with Vcc of +/- 12v and input sine wave of 5mV
peak at only 100Hz (yup, one hundred Hz). What?
Open loop gain of a 741 would give you a rail to rail square wave on
the output. You have to be limiting the gain external to the op amp
or your measuring method or instrument is wrong.
A 741 won't do Rail TO Rail. I think the fact it does square wave
in an open loop is what you're trying to convey in this situation.
To be honest, I haven't really found a spec anywhere that signifies
what Rail to Rail is. Every chip i've spec'ed as being rail to
rail, never reached it's actual rail voltages in the data sheet.
So some where, some one has decided what constitutes a rail level
output and what does not. Compared to what RR types do that are
currently out there, the 741 does not fall into that category.
Ditto that. "rail to rail," if specified, doesn't meet full