AVR-Chat

Low-side sensing is usually a better way (cheaper, higher 
performance, etc) unless the device you're monitoring insists on 
being connected to ground.

Analog Devices also makes a couple of good parts (and has a good 
sampling program):
  AD628 - Good for 100V CM 
  AD629 - Good for 270V CM

Their datasheets explain a lot of considerations that are necessary 
for accurate measurements.  The only thing I really hate about them 
is that they really work better with a + and - supply, but...

-Thor

--- In AVR-Chat@yahoogroups.com, mago Umandam <magzky02@...> wrote:
> Thanks a lot... Actually, i saw that IC on the net when i was 
searching for a solution.. But im having difficulty to find the IC. I 
am in singapore and i buy components from farnell only. Farnell 
singapore doesnt have LT6102. I dunno any electronics store here. 
Since a lot of guys are suggesting to put the sense resistor at the 
low side, i am planning to implement this and see how good this idea.
> 
> regards,
> mago 
> 
> Ned Konz <ned@...> wrote:                                  magzky02 
wrote:
>  > Hello all,
>  > 
>  > I am going to measure the current (0-500mA) on a system. i will 
be 
>  > using a current sense resistor, and an op-amp then i use ADC to 
>  > measure the opm-amp output. But my problem is that the the line 
is 
>  > high voltage (70 V). I am thinking to isolate the ground of the 
the 
>  > line and the ground of my monitoring box. In this case, the 
monitoring 
>  > box will not sence the 70 volt line as 70 volt, but will just 
measure 
>  > the voltage drop accross the current sense resistor. A idea on 
how to 
>  > measure current on high voltage systems is highly appreciated?
>  > 
>  
>  There are a number of current-sense amplifiers that do level 
shifting 
>  from high voltages.
>  
>  For instance,
>  http://www.linear.com/pc/viewCategory.jsp?
navId=H0,C1,C1154,C1009,C1077
>  
>  shows a table of Linear Technology's "current sense amplifiers".
>  
>  They have two parts that should do the job (they'll go to 100V 
>  common-mode voltage):
>  
>  LT6102HV
>  http://www.linear.com/pc/productDetail.jsp?
navId=H0,C1,C1154,C1009,C1077,P38188
>  
>  LT6101HV
>  http://www.linear.com/pc/productDetail.jsp?
navId=H0,C1,C1154,C1009,C1077,P12995
>  
>  These differ mostly in accuracy -- the LT6102HV is a zero drift, 
>  precision unit with 3mV max of offset voltage, while the LT6101HV 
has a 
>  maximum of 85mV of offset voltage (which may be higher than the 
>  current-sense voltage you're trying to monitor!).
>  
>  They have a current-mode output, so you set the overall gain by 
the 
>  choice of an output resistor, whose other end is tied to ground.
>  
>  Linear is selling the LT6102HV for 2.93 in single-unit quantities 
on 
>  their web site (SO-8 package).
>  
>  -- 
>  Ned Konz
>  ned@...
>  http://bike-nomad.com
>  
>      
>                        
> 
>        
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