I've used the Toroid Corporation of Maryland transformer I mentioned in
the previous post driving a bridge rectifier and a burden resistor with
success. As before, I like to put the resistor after the rectifier as that
minimizes the effects of diode forward drops (the secondary current source
forces the desired current through the burden resistor, somewhat
indpendent of how much voltage it takes). Another approach I've thought of
but have not tried would be to put the burden resistor right across the
transformer, then run it into a PIC analog input through a current limit
resistor. The PIC would half wave rectify the incoming AC. The clamp diode
would remove the negative side while the A/D would read the positive.
However, I've had trouble relying on clamp diodes with F series chips (I
had no trouble with C chips), so I'd probably still stick with the bridge
driving the resistor. The full wave rectification also gives you more
samples to compute RMS from.

Good luck!

Harold



> Resent with TAG.
>
> Rgs
> Ian
>
> -----Original Message-----
> From: Ian McLean [mailto:ianmm@optusnet.com.au]
> Sent: Friday, 20 February 2004 4:20 am
> To: 'pic microcontroller discussion list'
> Subject: RE: ] Current Transformers
>
>
> Hi all,
>
> Before anyone picks me up on this, I have been doing some more research on
> current transformers.  I don't need to rectify the secondary of the CT.
> Just put a 'burden resistor' (high watts, low resistance) straight across
> the secondary winding - then read the voltage across this resistor,
> op-amp,
> A/D input etc.
>
> Have I got this right ?
>
> Anyone know where I can get a suitable 50:5 CT from ?
>
> Or is there a "better way" ?
>
> Rgs
> Ian

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