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# Questions tagged [operational-amplifier]

Questions relating to the construction and applications of operational amplifiers,

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70 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 ...
179 views

### How build a practical AC over voltage protection circuit for the input of an arduino board

The input signal to my board is an AC signal. My board will process this signal. My board can handle 3.1Vpk-pk maximum without any damage occurring. In the event that my input signal exceeds that I ...
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 ...
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. ...
530 views

### High current from an op amp with or without transistors?

I have a 30Vppk signal (under 1MHz) which terminated to a 50 Ohm resistor. This is the output of the system. It can be optionally terminated by a 50 Ohm load or ** higher ** Z loads. With 50 Ohm load ...
214 views

### I don’t get this op amp exercise

Hi, in this exercise I need to find the values of Ra and Rb so that Vo is equal to Vx and Vy times an x value. I know how to find a equation with Rb, but I don’t know how to get an equation that ...
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 ...
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 ...
111 views

### Need help to analysis & overcome an issue with LM358 OP-AMP

I want to measure the resistance of a coil which its resistance vary in accordance with its temperature coefficient of resistance, the resistance range of the coil vary between 0.12 Ω to 5.00 Ω, at ...
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.
669 views

### Op Amp as a simple switch

I want to build a little voltage switch that switches on a buzzer and a relay when a certain voltage is reached. Please have a look at the schematic. I use a trim potentiometer to set up the switch ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
8k views

### Opamp: current flow in supply legs

Can somebody enlighten me on when and how much current flows in/out of the supply and/or ground leg of an opamp? What happens if there are resistors in those legs? Update 1: Here is the circuit that ...
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 ...
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 ...
283 views

### Common audio signal voltage range on Line out connector

What is typical audio signal voltage range on Line out connector of consumer electronic devices? (Vmin/Vmax) I need specify Input voltage range to calculate op-amp. ...
119 views

### Phase margin is 90 degrees but transient step response shows overshoot

The bode plot of the loop is as shown here The transient step response looks like this The block diagram looks something like this - Basically a single stage opamp(OPAMP in fig) with high gain(...
190 views

### op amp rails and its inputs

I am trying to feed this voltage measured by the oscilloscope to a voltage comparator. By design the voltage should swing between +0.7 and -0.7. BUT since the voltage is not referenced to ground I am ...
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,...
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 ...
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 ...
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 ...
83 views

I am using 3 similar op-amps (AD848JN) from Analog devices, tha name of the op-amps for clarification are Op-Amp #A,#B and #C. The configuration used to check the output offset is that one shown in ...
2k views

### Differential to Single-ended conversion clipping issue

I am attempting to convert the differential output of a DAC to a single-ended signal using the following circuit from a TI datasheet: The signals going into this amplifier look like this: And the ...
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 ...
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 ...
4k views

### What is the purpose of this op amp?

I am trying to build a pH meter using the below circuit. I am trying to understand the function of Op Amp U1. As I understand it, the LM4140A-1.0 is a voltage reference outputting 1.024V, which is ...
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 ...
1k views

### op amp level shift circuit diagram? [closed]

Can someone please help me with explaining the op amp level shift functioning with circuit diagram? Thank you
6k views

### Op Amp based Hartley oscillator

I would like to build an oscillator that will satisfy a few requirements. The main requirement is to have exactly one capacitor. Another one is to have high Q and sine wave output. I am considering ...
146 views

### Simple current regulator transfer function

I did simple op amp MOSFET current source. It was not working correctly, it had oscillations as per picture, so RC circuit was was added and problem was resolved. What I am wondering is transfer ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
49 views

### Laser diode feeding DIY driver

I am interested in feeding a laser diode (LD) with 2.5V and 210 mA. I am using basically a Darlington configuration as shown in the schematics. In order to prevent any damage to the LD I am using a ...
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 ...
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 ...
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 ...
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 ...