Hi,

I am using a hall-effect current sensor which outputs 60mV/A. At 0A the sensor outputs 600mV. Since the maximum current in my application is 5A, I am planning to amplify the output analog voltage using a non-inverting op-amp.
My problem is to set the virtual ground to 600mV, so that at 0A the output voltage is equal 0V and not 600mV. How can I archive this please?

 

hi dri,

This is an example of a Hall effect OPA with Offset.

The values could be modified to suit 600mV rather than the 1.5V on the original Hall device.

E

EDIT:
Added a modified circuit for 600mV offset.

The 11K on U3 could be a 25K pot to set the gain to suit your App.

 

hi dri,

This is an example of a Hall effect OPA with Offset.

The values could be modified to suit 600mV rather than the 1.5V on the original Hall device.

E

EDIT:
Added a modified circuit for 600mV offset.

The 11K on U3 could be a 25K pot to set the gain to suit your App.

Hi,

Can you please explain to me how the first part of the circuit operates?
Also, is R3 necessary?

Thanks.

 

Hi,

Can you please explain to me how the first part of the circuit operates?
Also, is R3 necessary?

Thanks.

hi,
I have added R3 in case you inadvertently connect the +inp pin to a higher voltage than the OPA supply, it will limit the input current. As the input impedance of the +inp is very high the 1K will not affect the performance of the OPA.

The left side OPA is a low impedance output DC Voffset source, used in the right side OPA to cancel out the +600mV base output voltage of the Hall device.

The right side OPA is an amplifier used to raise the low level signal from the Hall device to a suitable voltage level for an ADC etc..
E

 

Can I eliminate R5 and set the pot output to 600mV? Or can a pot set to output 600mV be connected directly to point "Vr" ?

Thanks.

 

Can I eliminate R5 and set the pot output to 600mV? Or can a pot set to output 600mV be connected directly to point "Vr" ?

Thanks.

If you eliminate R5 and just use a pot to set Voffset, you will have a problem setting it precisely. The measured value of vr will not be 600mV, it will be more due to the Gain of U3. [+1.17v]

If you connect a pot directly to Vr, every time you adjust the pot you will change the gain of U3, then you will have adjust the Gain of U3 and this will change the offset.!!

If you are prepared to adjust the Vr pot and the gain pot until you get the result you want, its possible to do it that way.

 

If you eliminate R5 and just use a pot to set Voffset, you will have a problem setting it precisely. The measured value of vr will not be 600mV, it will be more due to the Gain of U3. [+1.17v]

If you connect a pot directly to Vr, every time you adjust the pot you will change the gain of U3, then you will have adjust the Gain of U3 and this will change the offset.!!

If you are prepared to adjust the Vr pot and the gain pot until you get the result you want, its possible to do it that way.

Thanks for the reply. I want a gain of 4 so I set Rf as 300K and Rin as 100K. I removed the first op-amp and replaced it with a 1K multi-turn pot. This way, the 1K pot will not have a big effect of the gain since Rin is 100K.