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High-side current sensing at 120V

Question asked by Bernd60 on Jun 20, 2011
Latest reply on Jul 7, 2011 by Bernd60

Hello,

I am searching for a good idea to sense the current of 0 to 100 mA at a voltage level of  0V to 135V. The result should be a current to ground or a voltage respecive to ground. The first problem is the high voltage of 135V, the second, that this voltage can be nearly zero as well. I investigated several possibilities already:

 

  1. Use a shunt and OP or special circuits like the AD8210. Problem: not built for so high voltages. If I try to reduce the voltage by resistors, I bring in a source of error and the impendance of such a divider is so high that I change the amplification of the shunt amplifier too much.
  2. Use a hall-IC. Problem: The current is too small. Noise is too big.
  3. Use an opto-coupler. Problem: Current is too high for an LED. Bypassing some current produces non-linearities. Eventually a double coupler is needed with a second LED for compensation. This makes it too complicated.

 

As an additional point i have to concider that only little space is left on the pcb.

 

Does anyone have a (good) idea how to solve the problem?

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