DC current sensing continued

Now that the DC current sensing board has been finished - here are a few of the specs:

Vcc - 12V (15 on actual board)
Vbs - 12V (15 on actual board)

Here is the schematic and the PCB layout for variboard.







Initial problems occured when I did not reference Vin or Vout to GND. Once I fixed that up the results were a little better.



there are still a few problems:

1. the most obvious: why are all the signals going negative?
2. there is no current flowing through this setup, why is the square wave not 50%?
3. Why is the /OC pin going low if there is no current flowing?

Maybe I should connect both Vin and Vout to GND to make sure that no current is being sensed.



This scope plot is amost identical. Why? Why? Why?

Intersting to note that the of time is: 73.15ns and the off time: 6.749us

therfore the % on time is (73.15 * 10-3)/(73.15 * 10-3 + 6.749) = 1.1%. Something must be wrong with the measure function as I can see that that is not the case.


Okay... the negative problem was because I had the ground lead for the scope connected to the wrong track - see below. Still have other problems.



As I still have other problems, I thought that the problem may be the chip, however I get the same result if I change the chip.

My main problem is that there is no change in pulse width for a change in voltage across the V+ and Vs.

I am a tool. The "R" resistor that is meant to be 10 - 20R, I have used a 1K and it is open circuit anyway. Better change that to a 10R

Still a crap signal - home time now.