Hi all,

I don't know what I'm doing wrong here but I cannot get this voltage follower circuit to work correctly. Maybe I am misunderstanding a core concept here. I made the most basic voltage follower possible using the OPA376 op amp. I am using a breadboard to make all the connections but here is a circuit drawing. I have test point A and B in the drawing. My multimeter reads ~10mV from GND to point B (just as you would expect). But for point A my meter reads 4.93V. Isn't this circuit supposed to output 10mV?

I actually tried the same circuit on another closely related op amp the 2 channel OPA2376 (same datasheet) and I am getting the same result.

 

Do you have the correct pinout for the package you have?

 

Hello,

As @crutschow said, wich package do you use?



Bertus

 

Straight from my mouser order: part number: 595-OPA376AIDBVR.

I actually got some incorrectly labeled resistors from mouser before (package said 30ohm and I tested them at 300ohm). Maybe I should test the DCK pinout at least the supply voltages are the exact same pins.

 

We're still in suspense.
Which pinout did you use?

 

I have the DBV pinout so I am still confused.

Strange, I am apparently doing something repeatedly wrong. I just tried the follower circuit on a different DIP op amp (LM358) and I am measuring 3.75V on the op amp output. Repeatedly verified that the resistor divider (10kohm and 20ohm) give ~10mV at the op amp non-inverting input.

 

Are you counting the pin numbers from the top of the package, as shown?

 

Are you using cheap fake Chinese opamps from ebay?

 

No on the cheap Chinese op amps. Again I tried the voltage following on another op amp the LM358. Here's some photos to prove it, this is very frustrating. I've been stuck for days trying to make this simple voltage follower.

5V Power rails:


Resistor bias showing 10mV (5V power rail using 100k ohm + 200ohm resistors at the non inverting input of the op amp):


Now here is the wrench in my spokes, reading from the op amp output (1.417V):


And to make things even more confusing instead of using a jumper cable to reach my multimeter I pressed the multimeter lead directly to the op amp output pin and I get this reading (2.4mV):


Wtf is going on here? Why am I getting a different reading depending on which cable I connect to the multimeter? The inverting input of the op amp is shorted directly (with 2 jumpers in the breadboard just to make sure) to the op amp output..

Here's the pin out to the LM358 if anyone doubts my connections:

 

Please only measure directly on the IC pins. Be aware that those plastic plug-in breadboards sometimes develop intermittent connections.

 

Ah yes thanks. These breadboard connections are certainly a constant issue for me.

Update, I tried the 4th op amp in my collection and this one is finally working! Fourth time's the charm..

 

I stopped using a solderless breadboard about 50 years ago because most of my circuits built on them did not work even when I replaced the breadboards many times.
MANY threads on these electronics chat forums have people asking why their circuits do not work and the fault is that they were built on a solderless breadboard.

All my projects had the prototype soldered together on a layout-planned stripboard with all the strips cut as short as was possible so that each copper strip was used for many parts of the circuit resulting in a compact layout and low capacitance between different parts of the circuit. Many of my projects were a custom single circuit and the stripboard prototypes worked perfectly, were reliably soldered together and looked good enough to be sold as the finished products.

 

Have to agree with that. I stopped using them at about the same time for the same reason. Now everything is soldered, usually on phenolic boards with copper pads on 0.254 mm (1/10th inch) centers.

 

For 40 years, I have done almost all of my prototyping on solderless breadboards. A large number were just experiments and very few of them make it to a PCB.

 

Sounds like you have a bad chip, wiring, or breadboard.

 

I encounter the same problem. Created a simple voltage follower circuit using LM358, +/-12V power supply, 1 V on pin 3, and the reading on pin 1 and 2 is 10.5V. Have this problem been solved?

 

I encounter the same problem. Created a simple voltage follower circuit using LM358, +/-12V power supply, 1 V on pin 3, and the reading on pin 1 and 2 is 10.5V. Have this problem been solved?

Check the voltage on pin #4, you should have -12 volts.
SG