Mosaic
Well-Known Member
Hi all...I am using a precision, grounded, 0.1ohm resistor feeding the source of an NFET whose gate is driven by an lm358 OPA.
The OPA -ve is fed by the junction of the resistor & the Nfet source, thus the OPA causes the FET to limit current based on the voltage fed to its +ve input.
(Single supply, common 0V ground)
Are these following statements valid:?
Ok...since the input offset of the OPA is about 2mV. I assume that would imply that the opamp will cause an error of about .02Amp (.002/.1) selected by the +ve input voltage?
Eg. 1 v at OPA +ve in would require 10Amps dropping 1V across the .1 ohm sense resistor.
This can be perhaps 10.02 or 9.98 Amps based on the OPA offset error?
Now, since the OPA is supposed to output 0V once the differential between it's inputs are <=2mV then once the +ve input drops under 2mV the OPA should require 0 current flow in the sense resistor?
thx!
The OPA -ve is fed by the junction of the resistor & the Nfet source, thus the OPA causes the FET to limit current based on the voltage fed to its +ve input.
(Single supply, common 0V ground)
Are these following statements valid:?
Ok...since the input offset of the OPA is about 2mV. I assume that would imply that the opamp will cause an error of about .02Amp (.002/.1) selected by the +ve input voltage?
Eg. 1 v at OPA +ve in would require 10Amps dropping 1V across the .1 ohm sense resistor.
This can be perhaps 10.02 or 9.98 Amps based on the OPA offset error?
Now, since the OPA is supposed to output 0V once the differential between it's inputs are <=2mV then once the +ve input drops under 2mV the OPA should require 0 current flow in the sense resistor?
thx!
