# OPA547 - High power op amp connections check

#### Nabil Miri

Joined Jul 20, 2022
44
Hello all, I am using OPA547, a high-power op amp, to get about 700 mA from it (not continuous). I have simulated it using Microcap and got good results. The circuit:

I would be grateful if someone could confirm that my connections are correct and if I should add any other component to the circuit. Especially when implementing it physically and not by simulation.
Datasheet:
https://www.ti.com/product/OPA547

#### ericgibbs

Joined Jan 29, 2010
18,657
Hi Nabil,
Have you calculated the change in Vout, at pin#6 for a 1mA change in the current through R215.?

What is the lowest level of current change, you need to measure.
also
the Full range of currents expected in R215.?
E

For a practical circuit, add the required power supply decoupling.

#### Nabil Miri

Joined Jul 20, 2022
44
A 1mA change across R215 creates a 10mV increase from Pin 6. How does this info help?

#### kaindub

Joined Oct 28, 2019
120
Dont ever think you can go from simulation to final physical circuit in one go. The simulation is a toll to get you in the ballpark. You then need to make a prototype to see whether the physical circuit performs as the simulation circuit . Tweak and test again.
Seen it so many times that people go from drawing to final (PCB) layout and then wonder why it doesnt work.

#### ericgibbs

Joined Jan 29, 2010
18,657
A 1mA change across R215 creates a 10mV increase from Pin 6. How does this info help
hi,
I am trying to determine the specification you are working towards.?
1, Resolution, Accuracy of the current measurements.
2. Minimum & Maximum current values you expect.
3. The method of displaying the results.
+ any other relevant information needed to suggest a suitable design.

E

#### Nabil Miri

Joined Jul 20, 2022
44
Don't ever think you can go from simulation to final physical circuit in one go. The simulation is a toll to get you in the ballpark. You then need to prototype to see whether the physical circuit performs as the simulation circuit. Tweak and test again.
Seen it so many times that people go from drawing to final (PCB) layout and then wonder why it doesn't work.
Yes, that's what I am fearing. Thus, before physical testing, I created this thread to see if I was missing something in the simulation or not.

#### Nabil Miri

Joined Jul 20, 2022
44
hi,
I am trying to determine the specification you are working towards.?
1, Resolution, Accuracy of the current measurements.
2. Minimum & Maximum current values you expect.
3. The method of displaying the results.
+ any other relevant information needed to suggest a suitable design.

E
1. Resolution, not yet know the exact one but it is about 10/100 mircoA.
2. Min about 10 microA and Max is 1 Amp.
3. In general there is still another similar op amp that is connected after the R215 which acts as a current follower. Throught this op amp I will measure the current in the circuit as the amount of current will be converted to voltage. The output will be connected to an Ardino. I am thinking about putting several resistors in parallel with a switch to the op amp, and for certain range of current in the circuit there is a corresponding resistor that will be used to pass through this current and measure the output voltage.

#### ericgibbs

Joined Jan 29, 2010
18,657
hi N,
I have run this LTS simulation to compare with your results.
Next step: Which are the varying elements/components in this circuit, when the actual project is operating, that you want to measure the varying current values.?

E

#### Nabil Miri

Joined Jul 20, 2022
44
Thanks for trying to simulate it.
Resistances R234 and R235 vary in the circuit as they are some electrodes in a chemical cell. Moreover, the input voltage source V129 changes between +5 and -5.

#### ericgibbs

Joined Jan 29, 2010
18,657
hi N,
It is possible to simulate the circuit using possible changes in Resistances R234 and R235.
If you have an idea what these changes maybe, it would be possible to check the circuit out using those variable.?
E