I have an application where I need to monitor and
digitize the current waveform output of an audio power
amplifier into a subwoofer (speaker).
Previously, I used a hall-effect based sensor, but for
cost purposes (consumer product), it is impractical.
So instead, I have decided to use a 1 milli-ohm
current sense resistor. The problem now is creating an
electrical interface to convert the instantaneous
current (0 - 50 amps) into a proportional
instantaneous voltage (0-2.5v). Since the audio output
is not referrenced to ground, some type of
differential circuit must be used. But although the
voltage across the resistor will always be small, the
voltage at each of the 2 resistor taps, with respect
to ground can swing as high as much as +/-100 volts.
Unfortunately most instrumentation op-amps that can
handle such a high common-mode input voltage, are also
quite expensive. In addition, a textbook differential
op-amp circuit doesn't provide the needed accuracy,
even with .1% resistors, since any component
tollerance is multiplied by the gain of the circuit
(50). I though it would be easy finding an interface
circuit that would solve my problem, especially since
almost every DMM must use something similar for DC
current measurement. But I have had no luck. I would
appreciate some advice, even better a schematic.
Thanks


__________________________________________________
Do You Yahoo!?
Make international calls for as low as $.04/minute with Yahoo! Messenger
http://phonecard.yahoo.com/

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listserv@mitvma.mit.edu with SET PICList DIGEST in the body