First, let me say that my background is mechanical engineering. I have SOME EE coursework, but you may need to talk stupid to me
Okay, so I'm trying to get an exponential amplifier using a LM741 op amp to work. I'm using this basic model:
http://en.wikipedia.org/wiki/Operational_amplifier_applications#Exponential_output
Attached is what I have built. The supply voltage is 9VDC (attached to the rails at the bottom) and the input voltage difference is 2VDC. The potentiometer is a 1 MΩ pot. I adjusted the pot by 50 Ω increments and measured the output voltages (measured from the positive input at A17 to the negative output at J10 as per the attached picture) as shown below:
0 Ω 1.165 VDC
50 Ω 1.138 VDC
100 Ω 1.128 VDC
150 Ω 1.122 VDC
200 Ω 1.113 VDC
250 Ω 1.102 VDC
300 Ω 1.094 VDC
350 Ω 1.086 VDC
400 Ω 1.078 VDC
450 Ω 1.069 VDC
500 Ω 1.060 VDC
550 Ω 1.051 VDC
600 Ω 1.043 VDC
650 Ω 1.035 VDC
700 Ω 1.027 VDC
Correct me if I'm wrong, but this isn't an exponential output. My eventual goal is to take a small voltage (0.02VDC or so) and increase it by a factor of about 250 (yielding 5VDC). If I can't get it to work with a very standardized setup, I'm not sure what to do. What am I doing wrong?
**EDIT: Okay, so I realized some stupidity on my part. The output isn't exponential in relationship to the resistance. However, no matter what my setup, I cannot amplify a voltage ABOVE my input voltage. It's always <2VDC. Why?
Okay, so I'm trying to get an exponential amplifier using a LM741 op amp to work. I'm using this basic model:
http://en.wikipedia.org/wiki/Operational_amplifier_applications#Exponential_output
Attached is what I have built. The supply voltage is 9VDC (attached to the rails at the bottom) and the input voltage difference is 2VDC. The potentiometer is a 1 MΩ pot. I adjusted the pot by 50 Ω increments and measured the output voltages (measured from the positive input at A17 to the negative output at J10 as per the attached picture) as shown below:
0 Ω 1.165 VDC
50 Ω 1.138 VDC
100 Ω 1.128 VDC
150 Ω 1.122 VDC
200 Ω 1.113 VDC
250 Ω 1.102 VDC
300 Ω 1.094 VDC
350 Ω 1.086 VDC
400 Ω 1.078 VDC
450 Ω 1.069 VDC
500 Ω 1.060 VDC
550 Ω 1.051 VDC
600 Ω 1.043 VDC
650 Ω 1.035 VDC
700 Ω 1.027 VDC
Correct me if I'm wrong, but this isn't an exponential output. My eventual goal is to take a small voltage (0.02VDC or so) and increase it by a factor of about 250 (yielding 5VDC). If I can't get it to work with a very standardized setup, I'm not sure what to do. What am I doing wrong?
**EDIT: Okay, so I realized some stupidity on my part. The output isn't exponential in relationship to the resistance. However, no matter what my setup, I cannot amplify a voltage ABOVE my input voltage. It's always <2VDC. Why?
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