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Questions tagged [operational-amplifier]

Questions relating to the construction and applications of operational amplifiers,

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0answers
27 views

Why can not get maximum gain that can be achieved by LM358 op amps (Gain < 3.6 !!!)?

I need to amplify the PT100 (Temps Sensor) for giving it to Arduino, so I used this circuit with LM358 (V1 and V2 Value are not correct): And the V2 AND V1 are come from this circuit (based of ...
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1answer
32 views

Does MAX3665 amplifier have a minimum operating frequency?

I am using the MAX3665 in a design. The amplifier has an IR Photodiode at the input and is failing to detect any signals. My signal generator outputs a maximum of MHz square waves and MHz sine waves. ...
1
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0answers
39 views

RGB to YPbPr (YCbCr) conversion and bright picture issues

I'm working on a specific RGB to YPbPr (component) converter. It is supposed to connect old consoles to a modern flat 240p supportive TV. However I have an issue with luma Y output part. Here is the ...
1
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1answer
86 views

Op Amp voltage output without source connection

How do I go about calculating the voltage output for an operational amplifier when the only connection to the the voltage source is through the operational amplifier itself? For example, the diagram ...
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2answers
39 views

Calculation of noise in Non inverting Op-amp circuit

I have this non inverting op-amp circuit: I would like to calculate the output with the Op-amp noise impact. I can easily find the voltage output, but only if I assume there is no noise. How to do ...
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2answers
71 views

Op - Amp: Linearity, Negative Feedback and Virtual Short

I need some explanations about Linearity, Negative Feedback and Virtual Short for an ideal Operational Amplifier. Precisely, I have been always told that an operational amplifier with negative ...
0
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1answer
67 views

Is it a Rail-To-Rail opamp?

I ordered several LMC6482IN opamp without reading the datasheet details! I want to measure high side current with mA accuracy, for that I need the opamp output to go all the way to ground 0V. in the ...
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2answers
40 views

Inverting amplifier saturation with capacitor

R1 represents a resistive sensor in the figure below. In reality, it has also a capacitor in parallel. I'm trying to understand the effect of this capacitor. When a parallel C(is labelled as C2) is ...
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47 views

Understanding this current transformer conditioning circuit

See below a circuit used for current transformer signal conditioning. I have depicted the CT using the current source I1. I have the following questions: Are the 2 Pi filters really needed at the ...
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1answer
42 views

What is the difference between the order LP filter + Op-Amp and Op-Amp + LP filter in practice?

I have issues explaining what really happens on my circuit. I'm trying to make a cardiofrequencemeter with a white LED and a phototransistor. Basically I light the phototransistor, and measure the ...
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2answers
56 views

Op-Amp variable pulse generator

I'm having trouble designing a circuit using an Op-Amp (741) to generate pulses. The task given to me is: Design a pulse generator with a duty cycle that is adjustable from 0 to 100% and whose ...
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0answers
26 views

Error amplifier in PWM controller

Using the datasheet UC3842 PWM Controller I have modelled error amplifier in it. AC analysis of error amplifier matches with the datasheet plot(Figure 3) - Since I need to clamp the output ...
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2answers
79 views

Virtual Ground in op amp

The concept of virtual ground allows us to approximate both input terminals of an op amp at the same potential. People say that both the terminals are 'shorted'. Do this mean that the current can flow ...
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2answers
82 views

How to protect an op-amp against high inrush current following a high input voltage pulse?

I have a circuit where I'm amplifying the output of a piezo transducer with an op-amp. By taking some readings, i've found that the piezo can output fairly high voltages when struck hard (~20V), and ...
0
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1answer
75 views

ADC with small input range

All of the ADCs I found online have an input range on the order of few volts, e.g. 0 to 5 or -4 to +4. But my signal is in the mV range. Are there any ADCs with such a small input range? I know I can ...
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1answer
30 views

Low power rectification of AC component of modulated current signal

I have a current source consisting of a 100Hz sine plus a DC offset: \$I=I_{DC}+I_{AC}\cdot\sin(2\cdot\pi\cdot 100Hz\cdot t)\$ with \$ I_{DC}\approx100uA\$ and \$I_{AC}\approx 1uA\$. I would like to ...
4
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1answer
1k views

How does it work when multiple companies sell the same IC? [on hold]

Very common ICs are sold by many manufacturers, for example let's say the TL07x range (which is vintage, but does demonstrate the case). Inspecting datasheets of two manufacturers, TI and Diodes Inc,...
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2answers
67 views

Non-inverting amplifier with variable gain from 1 to 15

I need to design a non-inverting amplifier with gain from 1 (unity) to 15. From what I read, in theory this can be achieved by using a pot as the feedback resistor, but in practice this will only work ...
1
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1answer
54 views

Gain bandwidth plot of an opamp

The gain and bandwidth product of an ideal op amp is always constant. This statement seems to be true in the '-20dB slope' region. But this doesn't seem to be true for the low frequency region. The ...
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1answer
40 views

A circuit with a non-inverting op-amp and comparator for amplifying the output of a piezo transducer. Am I missing anything?

I'm a total noob when it comes to electronics so was hoping some people might be able to take a look at my circuit and see if it makes sense. I'm trying to create a circuit which amplifies the puny ...
1
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1answer
29 views

Voltage follower with shift

I am trying to figure out a simple application/ circuit that would allow me to shift the voltage a little bit. Lets say we have an input voltage of range from 0 to 1 V. I need an output voltage of 0.2 ...
1
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1answer
37 views

Computer controlled potential difference across wires

I am trying to design a circuit to control the potential difference across 2 stainless steel wires. The two wires are connected together at one end (common node) and on the other end, one wire is ...
0
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1answer
69 views

Opamp output short circuit protection

I am trying to build a voltage generator 0-10V to feed the input of a PLC ADC card (for simulation purposes). The PLC card has an input impedance of 133k. I am thinking to use the circuit from the ...
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1answer
52 views

Help with Op amp Circuit Design

Given the blue transfer function graph, I want to design a circuit that can replicate the characteristics, preferably using an op amp. This is what I have done: where the red circuit is the red curve ...
2
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1answer
38 views

Requirements for low voltage, low current MOSFET used in current source

I'm trying to determine the minimum requirements for a MOSFET that will be used in a op-amp based current source. I've hit Google and this site and looked at multiple pages, but almost always, they ...
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1answer
65 views

Design of Low Pass Filter

So I have made a low pass filter and plotted the transfer function of it. However, I know I need to also use another opamp to correct the phase shifting/ gain. What design should be best to add on to ...
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0answers
26 views

how to increase the sensitivity of a home-built locked in amplifier?

I am building a locked in amplifier from scratch for an optoelectronic device using a couple of boards in conjunction with the STEM Redpitaya. The System configuration is as follows: Signal(coming ...
2
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2answers
49 views

Hand contacting op amp photodiode circuit causes interference - what ist the physic behind it?

I am new to analogue electronics and I am still learning about op-amps. I use the most common circuit for amplifying a photodiode's signal to measure it with an ADC: Amplification gain is 1M, the ...
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2answers
29 views

current limiter after a voltage divider for op amp input

I am doing a two-stages amplifier for a very small signal (-+300uV), coming from a radar sensor. The following two images are taken from application notes. I know R2 and R3 are voltage divider. 2.5V ...
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1answer
36 views

Simulating matching op-amp input impedance with offsets

I have a current source with RC filter at the input of an LM324 op-amp configured as a buffer. The Input Biasing Current is 45nA and the Offset Current is 5nA for the LM324.The input resistor is 750k ...
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1answer
46 views

SMPS feedback circuit with voltage regulation and current limiting

i’m self learning electronics for a few months now and i choose my first project to be a bench SMPS. Since it is my first circuit design ever i really need some clarification. My SMPS is 2-switch ...
2
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1answer
64 views

Can electrical noise cancel itself out?

If two independent noise sources are added together, their noise adds up like so: $$RMS_{sum} = \sqrt{RMS_1^2 + RMS_2^2}$$ Am I correct to assume that this only holds if the noise sources are ...
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0answers
35 views

op amp saturation

I have this circuit which is acting with negative resistance. However when increasing the voltage well above saturation it produces a weird distortion on the output as seen below. can anyone explain.
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2answers
40 views

Calculate closed loop gain with Oscilloscope measurements

Using these reading from Agilent MSO-X2012a oscilloscope: from this circuit: How do you calculate the close loop gain using these measurements. I already calculated by hand and got Av = 11V.
4
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4answers
361 views

Limiting sensor input voltage without biasing measurement

I need to measure precise voltage in the range from 0.375 volt to 10.1 volts from a source with 100ohm impedance. Maximum voltage however, may be well above 10.1V, so I need to be sure I do not ...
0
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1answer
74 views

What kind of Op Amp configuration is this?

I am trying to understand the circuit that is a part of a sensor module. I don't know what exactly it is doing. The Vin signal is an AC signal.
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1answer
146 views

Why do we need a 2kOhm resistor

What is the purpose of the 2k resistor in the schematic below? I am guessing the current through the diode will be infinity if it were absent?
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2answers
31 views

Question regarding Transresistance Amplifier Circuit

Something that makes me confused while reading a tutorial on the Transresistance amplifier circuit. Here is the picture of the circuit. It basically measures the current across the photo device and ...
0
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1answer
12 views

Protection for power-off case with active input

My application is roughly depicted in the attached image. I am sensing a Vin voltage, by dividing down with a resistive divider, then passing the signal through an opamp and an RC filter (not shown) ...
2
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3answers
83 views

Solving Op amp Voltage output

With the following circuit: There is a resistor (R2) in front of RL. So how would you find Vout? I already know the formula for finding Vout (Vout = -(RF/R1) X Vin), but what do you do with R2 in ...
2
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1answer
66 views

My very basic voltage-controlled amplifier gives an asymmetric waveform?

I want to build a voltage-controlled amplifier. The Wikipedia pages on voltage-controlled amplifiers and voltage-controlled resistors suggested using the following approach: first I would simply build ...
2
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3answers
775 views

How do I compute the closed-loop gain when using an op-amp with finite open-loop gain?

my future fellow Electrical engineers. I can't figure out how one gets -500(b) as the Open-loop gain. Using node analysis: \$i_1 = \frac{v_- - v_{in}}{100 Ohms}\$ \$i_2 = \frac{v_- - v_{out}}{100k ...
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4answers
4k views

Why exactly does maximum power transfer happen at 50 ohms (matched impedance)?

As the title mentioned - I am not sure why exactly the maximum power delivered to the load will be max when R_L is 50 ohms. If I guess why, it's because if the resistance was greater than 50 ohm then ...
1
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1answer
52 views

Opamp input offset voltage when saturation

I wonder, how to affect the input offset voltage of inverting amplifier when it's output in saturation? I'm changing gain with decreasing the value of R2. When the gain is greater than 5, output in ...
0
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2answers
39 views

Interpret the arrows in a circuit diagram of an OP-amp

I have the following diagram of an ideal OP and $$ y=-Ae \tag 1 $$ simulate this circuit – Schematic created using CircuitLab I'm not used of using arrows for voltages, so I don't grasp the ...
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0answers
41 views

Do I need a headphones amp for this?

I have a digital piano with a headphones jack built-in. It's a Kawai CN27 if it matters. When I play the piano with headphones on I would like to mix in the audio signal from my phone's headphones ...
1
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1answer
46 views

MCP604 op-amp output seems to jump to the positive rail

I'm hoping someone can give me some insight as to what's going wrong with this MCP604 op-amp. I'm seeing this issue on about 150 of the ICs. Below are some specs for the MCP604 and an image from my ...
3
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1answer
100 views

Inverting op amp design saturates at a fraction of power supply

I have built a simple inverting op amp. I am applying a 1 Vpp sinusoid at 10 Hz to a design with ~4.7x gain. The resistors I am using are 47kOhm and 10 kOhm. The op amp chip is the LT1222, and I am ...
4
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3answers
429 views

AD823 current sense

Refer the attached schematics. Consider the details mentioned in it. I want to build the current sensing scheme using the part AD823 . enter link description here I understand that offset correction ...
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1answer
81 views

Lt spice op amp phase margin

I created a lt spice model of my circuit which consists of an op amp in a unity gain voltage follower configuration which feeds a SAR ADC. I also included the flywheel circuit in front of the adc. ...