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Results tagged with operational-amplifier
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user 6127
Questions relating to the construction and applications of operational amplifiers, which are DC-coupled, high-gain electronic voltage amplifiers with a differential input and, usually, a single-ended output.
0
votes
Replacement for 747 opamp (dual 741)
I can only assume that you're using a 741 or similar because you need the offset null. If you need zero input offset voltage you can use a chopper op-amp like the OPA2180. Chopper opamps have an input …
- 4,309
0
votes
Op amp voltage follower saturates (high-rail) at 0V
Called phase reversal. It happens when you use the opamp outside its specified common mode input range.
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5
votes
Non-inverting op-amp amplifier gain as open-loop gain goes to infinity (limit calculation)
\$\infty/\infty\$ is an indeterminate form, so use L'Hôpital's rule
$$\lim_{A\rightarrow\infty}\frac{A}{1+A\frac{R_1}{R_1+R_F}} = \frac{\frac{d}{dA}(A)}{\frac{d}{dA}(1+A\frac{R_1}{R_1+R_F})} = \frac{ …
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1
vote
Is this a true corollary about Ideal Operational Amplifiers?
The voltage gain of an ideal opamp is infinity, so if there was any voltage difference between the inputs there would be infinite voltage at the output.
Ok, so this was probably a mistake right? T …
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2
votes
Op Amps: how do they know whether the supply is split?
Consider a graph of \$V_+-V_-\$ vs \$V_{out}\$ (referenced to \$V_{SY}^-\$) for the two equations given. The opamp can't produce more than \$V_{SY}^+\$ or less than \$V_{SY}^-\$, of course.
Here yo …
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15
votes
Are the offset voltages in a dual/quad op amp correlated?
No.
The offset voltage comes from the difference between the two input transistors in the same opamp.
The input transistors in this TL072 are interleaved so that they have the same center, so that if …
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1
vote
Overcoming vbe in a low voltage application
Use a PNP instead of an NPN and swap the inputs, but don't forget to compensate for the extra gain. Here C1 sends any high frequency directly to the input, slowing the opamp's response, and miller-mul …
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2
votes
Accepted
0.5V virtual ground with single rail op amp
If VGND is 0.5V and is sinking current, what would the voltage at the base of Q21 need to be?
If VREG is 3.88V and is sourcing current, what would the voltage at the base of Q23 need to be?
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1
vote
Unusual opamp topology: driving a dummy load and using supply currents to drive common-source
Sometimes called bootstrapping.
See also this (recent) question: Increasing Speed of Bootstrapped Amplifier
Advantages:
Disadvantages:
1
vote
Accepted
Why do designers use op-amps with fractional gains?
Why not use just a voltage divider? It decouples the input and output circuits.
The output impedance is low
The input impedance is R1
The load has no effect on the input impedance
The last one is …
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6
votes
Accepted
Transistors on op-amp power rails
Your second schematic allows Vcc-Vee to be higher than the opamp can handle. The two small transistors keep its vcc/vee dc biased at +-19V which is as high as it can handle. The darlingtons use the +- …
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1
vote
Extend linearity range of this opamp circuit
Swap the load and MOSFET.
simulate this circuit – Schematic created using CircuitLab
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0
votes
Is transistor in cutoff?
When the voltage at the non-inverting input increases, the output voltage increases and so the voltage at the inverting input decreases. This is positive feedback. The virtual ground concept only appl …
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4
votes
Accepted
My non-inverting amplifing circuit is always giving constant output values
Read the datasheet before choosing an op-amp.
You are violating the recommended supply voltage range
and the input common-mode voltage range
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1
vote
How to keep decompensated op amp in linear region?
The second one probably would have worked if Q1 was instead a MOSFET. Both introduce substantial nonlinearity near the threshold. Here's an alternative.
Something like this:
simulate this circ …
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