OP07 Op Amp Output Unexpectedly High Voltage

In summary: For frequencies above 6 kHz, the gain will be lower. You need to write out and solve the circuit equations.Use opamp equation V(out) = G[(Vin+)-V(in-)] where G is 400,000 (for OP07).So V(in-) = V(out)*1k/(100k + 1k) = V(out)/101V(in+) = V(sig)So V(out) = G*V(sig) - G*V(out)/101Re-arranging;V(out) = 101*V(sig) / (1 + 101/G
  • #1
m718
88
0
When I connect 3V negative and 3V postive power supply to an OP07 op amp and I Connect a voltmeter to OUT of op amp and GROUND the voltmeter shows -1.8 volts
why? I have connected anything to input I even tried shoring the input and this voltage is too high to be offset voltage. I Tried two OP07s, a tl071cp and a 741 they all show voltage between 1.5 and 1.8, why is it showing this high voltage?
 
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  • #2
Connect the op amp output to the neg input, and the pos input to ground. This is a voltage follower circuit, and the output ideally should be zero volts (same as ground). because of the input offset voltage, You should read about 100 microvolts on the output to ground.
 
Last edited:
  • #3
Bob S said:
Connect the op amp output to the neg input, and the pos input to ground. This is a voltage follower circuit, and the output ideally should be zero volts (same as ground). because of the input offset voltage, You should read about 100 microvolts on the output to ground.

Ok I will do that but then where do I connect the input signal it will be an antenna or dynamic mic.
 
  • #4
m718 said:
Ok I will do that but then where do I connect the input signal it will be an antenna or dynamic mic.

Bob was answering your question about how to measure the input offset voltage. To connect a microphone or other sensor, un-ground the + input, and connect one lead of the mic to it, and the other end of the mic to ground. The opamp will serve as a follower for the mic voltage (a current and power amplifier, but not a voltage amplifier).

Quiz Question -- how do you turn the opamp stage into a voltage amplifier, either inverting or non-inverting in configuration?
 
  • #5
berkeman said:
Bob was answering your question about how to measure the input offset voltage. To connect a microphone or other sensor, un-ground the + input, and connect one lead of the mic to it, and the other end of the mic to ground. The opamp will serve as a follower for the mic voltage (a current and power amplifier, but not a voltage amplifier).

Quiz Question -- how do you turn the opamp stage into a voltage amplifier, either inverting or non-inverting in configuration?

ok thank you, I don't know how to make it a voltage amp. Using a resistor somewhere but I don't know where
 
  • #6
m718 said:
ok thank you, I don't know how to make it a voltage amp. Using a resistor somewhere but I don't know where

Then it appears that you have some fun learning about how to use opamps ahead of you. What learning resources do you have available? What course are you working on, or is this self-study?
 
  • #7
berkeman said:
Then it appears that you have some fun learning about how to use opamps ahead of you. What learning resources do you have available? What course are you working on, or is this self-study?

I'm just reading online about op amps.
How do I make it a voltage amplifier??
 
  • #8
m718 said:
I'm just reading online about op amps.
How do I make it a voltage amplifier??
Now that you have connected the mic signal to the positive input, disconnect the wire from the output to the negative input and in its place put a 100k resistor. Connect a 1k resistor from the negative input to the common (power supply) ground. Now connect a 1k resistor from the positive input (where the mic signal is already connected) to the same common ground. Now connect the mic ground to the common ground.

You need to write out and solve the circuit equations

Use V(out) = output
V(in+) = positive input
V(in-) = negative input
V(sig) = signal

Use opamp equation V(out) = G[(Vin+)-V(in-)] where G is 400,000 (for OP07)

So V(in-) = V(out)*1k/(100k + 1k) = V(out)/101

V(in+) = V(sig)

So V(out) = G*V(sig) - G*V(out)/101

re-arranging;

V(out) = 101*V(sig) / (1 + 101/G) =approx 101*V(sig) for G>>101 voila!

Note that the circuit gain depends on the two feedback resistors and not on G.

Now if the opamp has a unity gain-bandwidth of 600 kHz, then the circuit gain should be close to 101 for frequencies below 6 kHz.
 

1. What is an OP07 op amp and how does it work?

The OP07 op amp is a type of operational amplifier, or op amp, which is a highly versatile and widely used electronic component in the field of analog signal processing. It works by taking an input voltage and amplifying it to produce a larger output voltage. This amplification is achieved through the use of internal circuitry and feedback loops.

2. Why is the output voltage of my OP07 op amp unexpectedly high?

There could be a few reasons for this. One possibility is that the op amp is being operated outside of its recommended supply voltage range, causing it to produce a higher output voltage than expected. Another possibility is that there is an error in the circuit design, such as incorrect resistor values or incorrect connections.

3. How can I troubleshoot and fix the issue of high output voltage in my OP07 op amp?

To troubleshoot this issue, you can start by checking the supply voltage and ensuring that it is within the recommended range. If that is not the issue, then you can carefully review your circuit design and check for any errors. You can also try replacing the op amp with a new one to see if that resolves the issue. If the problem persists, it may be necessary to consult a professional or refer to the op amp's datasheet for further guidance.

4. Can the high output voltage of an OP07 op amp damage other components in my circuit?

Yes, it is possible for the high output voltage of an op amp to damage other components in the circuit if it exceeds their voltage rating. This is why it is important to ensure that the op amp is operating within its recommended supply voltage range and that the circuit is designed correctly.

5. Is it possible to reduce the high output voltage of my OP07 op amp without affecting its performance?

Yes, it is possible to reduce the output voltage of an op amp by adjusting the feedback resistors in the circuit. This will not significantly affect the performance of the op amp as long as the feedback loop is stable. However, it is important to note that reducing the output voltage may also affect the overall gain and accuracy of the op amp.

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