Measure Operation amplifier problem.

[boki]

Dear All,

We often simulation op-amp plus a load capacitor, but in theory, the
AC signal will pass capacitor, if we connect load capacitor at op-amp
output, will the AC output signal pass to ground? or how to explain it
?

Thanks!


Boki.

 

[Winfield Hill]

boki wrote...

We often simulation op-amp plus a load capacitor, but in theory, the
AC signal will pass capacitor, if we connect load capacitor at op-amp
output, will the AC output signal pass to ground? or how to explain it?

Boki, are you happier thinking of an ac current passing to ground,
proportional to the signal voltage and frequency? i = 2 pi f C v
This current, if you like, is what the opamp must struggle with.

Thanks,
- Win

whill_at_picovolt-dot-com

 

[MikeM]

boki wrote:

Dear All,

We often simulation op-amp plus a load capacitor, but in theory, the
AC signal will pass capacitor, if we connect load capacitor at op-amp
output, will the AC output signal pass to ground? or how to explain it

When you "close the loop" on an opamp, the output impedance is lowered,
making the output appear to be a voltage source, possibly making you
think that it could drive anything...

However, the amplifier has a "how much current can it deliver" spec which you
have to look up on its spec sheet. If you connect a capacitive load to
an opamp, the load impedance that the amplifer sees decreases at higher
frequencies. The ac signal current at these higher frequencies can
overwhelm the amplifier's ability to deliver it, causing severe distortion,
phase shift and possibly oscillation. Usually, a resistor is added
between the amplifier's output pin and the capacitive load to limit the
peak current to something the amplifier can handle.

Mike M

 

[boki]

Soga, thank you very mcuh!

Regards,

Boki.

Winfield Hill <Winfield_member@newsguy.com> wrote in message news:<c4rhe102u8j@drn.newsguy.com>...

boki wrote...

We often simulation op-amp plus a load capacitor, but in theory, the
AC signal will pass capacitor, if we connect load capacitor at op-amp
output, will the AC output signal pass to ground? or how to explain it?

Boki, are you happier thinking of an ac current passing to ground,
proportional to the signal voltage and frequency? i = 2 pi f C v
This current, if you like, is what the opamp must struggle with.

Thanks,
- Win

whill_at_picovolt-dot-com

 

[Boki]

Thank you very much,

Best regards,
Boki.

"MikeM" <trashcan@yahoo.com> ??? news:c4rs6r$rru$1@coward.ks.cc.utah.edu
???...

boki wrote:
Dear All,

We often simulation op-amp plus a load capacitor, but in theory, the
AC signal will pass capacitor, if we connect load capacitor at op-amp
output, will the AC output signal pass to ground? or how to explain it

When you "close the loop" on an opamp, the output impedance is lowered,
making the output appear to be a voltage source, possibly making you
think that it could drive anything...

However, the amplifier has a "how much current can it deliver" spec which
you
have to look up on its spec sheet. If you connect a capacitive load to
an opamp, the load impedance that the amplifer sees decreases at higher
frequencies. The ac signal current at these higher frequencies can
overwhelm the amplifier's ability to deliver it, causing severe
distortion,
phase shift and possibly oscillation. Usually, a resistor is added
between the amplifier's output pin and the capacitive load to limit the
peak current to something the amplifier can handle.

Mike M