RE: Differential voltage probes 3

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

Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>

Hi,

Ok, using bleeding edge, oh!, I mean leading edge parts...  I got it back 
down to one IC.

http://hot-streamer-dot-com/temp/DiffProbe21.gif

The fabulous Ti THS4151ID apparently does all the power supply offsets and 
CMRR fixing internally.  That chip is basically the whole enchaladia!   So 
I just added Ohmite's little 5kV resistors, some 1% 1K resistors, some big 
NPO caps and it's done.  It would almost fit on a quarter ;-)

There are some relatively expensive parts now, but the total cost is not 
that much.  The input resistors are $4 each, the IC is $9, the NPO caps are 
$2...  But I think the total cost would be about $45.  Yes, it is all that 
little surface mount stuff and you have to be careful since the high 
voltage is very near.  Probably a good candidate for HV conformal coating...

The input resistors are 5%, but hopefully they are somewhat matched as they 
come off the reel.  The PCB around those resistors would have to be routed 
out to insure voltage standoff.

I have no idea what the frequency response would be, but it "should" be 
pretty darn high!  The IC is 150MHz and I am feeding it just like it 
wants.  With the input resistors being so small, a LOT of response problems 
just vanish.  Caps across the 1k resistors could limit the frequency 
response if needed.

Unless someone has a better idea, I think I will give this one a try.

Cheers,

	Terry