I need to sense current of a power supply. Sense resistor is before the pass transistor, where I have 45 V appr.
I've selected one differential amplifier apt for up to 100 V
Please check here:
http://www.national.com/ds/LM/LM725.pdf
After trying for days to make it work, by mistake I found that to work properly, the supply feeding the opamps must be independent of that from the power supply.
Since what I need is its Vout to help in limiting the current I am sensing, here are my questions:
a) Why in heaven is this happening?
b) How to relate the Vout of this amplifier to the rest of the power supply circuit where I need to limit the current I am sensing?
It seems that the separate supply for the opamp and the use of its Vout in the circuit under sensing is contradictory?
CAn anyone help me?
Gracias
I've selected one differential amplifier apt for up to 100 V
Please check here:
http://www.national.com/ds/LM/LM725.pdf
After trying for days to make it work, by mistake I found that to work properly, the supply feeding the opamps must be independent of that from the power supply.
Since what I need is its Vout to help in limiting the current I am sensing, here are my questions:
a) Why in heaven is this happening?
b) How to relate the Vout of this amplifier to the rest of the power supply circuit where I need to limit the current I am sensing?
It seems that the separate supply for the opamp and the use of its Vout in the circuit under sensing is contradictory?
CAn anyone help me?
Gracias