Hi piclisters.

Take a look at LEM products.

www.lem.com


Regards.

Luis


> -----Mensaje original-----
> De: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]En nombre de Sanjay Punjab
> Enviado el: domingo 29 de julio de 2001 12:08
> Para: PICLIST@MITVMA.MIT.EDU
> Asunto: [EE]: Having difficulty interfacing a current sense resistor to
> create a proportional voltage
>
>
> 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
>
>
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