Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Op-Amp with ref voltage

Status
Not open for further replies.

drkidd22

Member
So I have this op-amp circuit I can't get my head around.
It has a reference of 10V on the non-inverting input and an input voltage of 9.98V.
Wouldn't my output then be (Vin-Vref) * R2/R1. Which would be an output of 6.06V? But I get 16.06V.
Capture.PNG
 

Attachments

  • opAmpTest.asc
    1.4 KB · Views: 108
16.06 is correct. Just think about - you have a lower voltage at negative output - so therefore the output voltage HAS TO BE higher than Vref.
 
Perform the next two simulations;
1 make both supplies exactly 10 volts

2 make both supplies exactly 9.5 volts.

In both instances measure Vout
 
So my equation turns into [(Vin-Vref) * R2/R1] + Vref?
Because Vin is an inverting input it's actually [-(Vin-Vref) * R2/R1] + Vref
 
So I've built 2 circuit similar to the original. The only difference is that one is built with an OP279 and the second circuit is built with a OPA2340.
Now with the same imput voltage the output is significantly different. Could this be due to the input offset voltage?
I get a wider swing with the Op279 than the OPA2340.
 
Have you compared, on their individual datasheets, what is the Voh for each device with a load of well over 10 mA?
 
Have you compared, on their individual datasheets, what is the Voh for each device with a load of well over 10 mA?
The OP279 has Voh of +4.8V and Vol of 75mV. I can't find the Voh or Vol on the datasheet of the OPA2340.
The OP279 does have a supply range of 4.5V to 12V while the OPA2340 is 2.5V to 5.5V.
 
Its there, but shown in not explicit way, on the chart: Figure 15. Output Voltage Swing vs Output Current

Do something: significantly reduce the load current, at least by a factor of 10X, and measure/simulate again.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top