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:
- 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.
- Use a hall-IC. Problem: The current is too small. Noise is too big.
- 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?