Re: Terry's Differential Probe Circuit

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>

Hi Dan,

At 02:01 PM 2/26/2004, Terry Fritz wrote:
>Terry,
>
>In regards to your differential amp probe design you were working on,
>you said you were having some problems with it.
>Were those problems simply related to compensation or do you think it
>was more a function of the device you were
>using (THS4151).

Compensation was very hard.  I soldered and un-soldered dozens of little 5, 
10, 50... pF NPO caps...

Offset was also a problem.  The dividers were like 1000:1  Any little 
offset had to be adjusted out.  The chips were very nice. but not that nice.


>I'm looking to use a differential type amplifier to sample the output of
>my new SSTC controller, which will then be
>connected a BNC output at the front panel to be used with an
>oscilloscope.  Basic requirements are at least 1MHz bandwidth, and able
>to sense at least +2000V/-2000V.  Since I'm only interested in a general
>waveform view, i'm not worried about
>any small amounts of distortion or droop or other problems which might
>be associated with a poorly compensated amplifier.

If you want the parts I have, I would be happy to send them to you.  Maybe 
you can figure it out.


>If you could provide some details and any lessons learned, it would be
>appreciated.

I learned that the $1000 TEK diff probes are a great deal!! ;-))


>Another approach is using a simple voltage-sampling transformer.   I'm
>still looking into both.

Let me know if you want the parts here.  I finally had to give up.  I 
"could" get it to work, but I needed fare more equipment to do it than was 
practical.  If you are not trying to do super high frequency and all, 
things would be much easier.

Cheers,

         Terry



>Dan