PSN-L Email List Message
Subject: RE: line driver question
From: "Keith Payea" kpayea@...........
Date: Wed, 15 Mar 2006 21:12:12 -0800
Barry:
The circuit you describe is the classic way to deal with a large capacitive
load on an op-amp. The series resistor decouples the capacitance from the
op-amp output, and the local feedback capacitor keeps the whole thing
stable. There are also op-amps which are designed to drive highly
capacitive loads like this. It's not so critical if you don't need high
gain in addition to the line driving capability.
I use a part called the LM837 in my VBB output to drive the 70 or 80 feet of
cable back to the SDR system. See the schematic at:
http://www.bryantlabs.net/Images/SenseAmp.pdf You can see I have a small
resistor in series with the output also.
You are right to add a buffer between the internal "Analog Computer" and the
cable. I agree the issue is not so much the added capacitance as the
potential to feed noise into the process back up the cable. Opamps are
cheap...
Cheers,
Keith
_____
From: psn-l-request@.............. [mailto:psn-l-request@............... On
Behalf Of Barry Lotz
Sent: Wednesday, March 15, 2006 8:46 PM
To: psn-l@..............
Subject: Re: line driver question
John,Brett,Richard&Geoffrey
Thanks for the "feedback" :). All I am trying to do is monitor a voltage
in a feedback circuit from 40' from the circuit without affecting the
performance of the feedback circuit. The monitored voltage goes to a LCD
voltage display in my house.I think I will just try a follower with a
resistor at the output , to prevent transient voltages from entering the
feedback circuit from the shielded line.
regards
Barry
Barry:
The circuit you describe is the classic way to =
deal with a=20
large capacitive load on an op-amp. The series resistor decouples =
the=20
capacitance from the op-amp output, and the local feedback capacitor =
keeps the=20
whole thing stable. There are also op-amps which are designed to =
drive=20
highly capacitive loads like this. It's not so critical if you =
don't need=20
high gain in addition to the line driving =
capability.
I use a part called the LM837 in my VBB output =
to drive the=20
70 or 80 feet of cable back to the SDR system. See the schematic =
at: http://www.bryantl=
abs.net/Images/SenseAmp.pdf =20
You can see I have a small resistor in series with the output=20
also.
You are right to add a buffer between the =
internal "Analog=20
Computer" and the cable. I agree the issue is not so much the =
added=20
capacitance as the potential to feed noise into the process back up the=20
cable. Opamps are cheap...
Cheers,
Keith
John,Brett,Richard&Geoffrey
Thanks for the "feedback" :). All I am trying to do is =
monitor a=20
voltage in a feedback circuit from 40' from the circuit =
without=20
affecting the performance of the feedback circuit. The monitored voltage =
goes to=20
a LCD voltage display in my house.I think I will just try a follower =
with a=20
resistor at the output , to prevent transient voltages from =
entering the=20
feedback circuit from the shielded line.
regards
Barry
[ Top ]
[ Back ]
[ Home Page ]