Questions tagged [comparator]

A comparator compares two voltages or currents and switches an output to indicate which is larger.

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1answer
2k views

Can I use differential I/O pins of FPGA as high speed comparator?

High speed comparators are rather expensive and speed is what FPGAs are very good at. On the other hand, FPGAs (in my case: XC3S400) have paired differential pins in each bank that their voltages are ...
0
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1answer
575 views

AD9850 comparator problem. How to calculate is frequency?

I want to convert a sine wave produced from AD9850 (opens *.pdf) into square wave with its inbuilt comparator. AD9850 has a fast comparator with 3ns rise/fall time and propagation delay= 5.5ns. ...
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2answers
300 views

Preset ratings for a comparator circuit

1)What are the rating for these kind of presets? I need the maximum current they can withstand without any harm, (Imax). [data need for a 100k preset] 2)I'm hoping to use this kind of voltage ...
1
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1answer
586 views

Comparator circuit to detect working alternator

I'm very new to electronics, but am trying to build a device that should be attached to a motorcycle (Arduino based sensor board) which should only draw power when the engine is running; specifically ...
2
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0answers
184 views

comparator input latches high?

I am using a a TI TLV3202 comparator (U2B) with a bridge circuit as shown in the schematic below. It is followed by a DG4157 analog switch. This is related to this question I had asked earlier. ...
3
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1answer
2k views

LM311 comparator output

In the LM311 circuit below that is used as a comparator, how does voltage at the reference (- Input), affect the output? For a sine wave, would having a higher voltage at the reference increase or ...
3
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3answers
662 views

Basic comparator strange problem

I am trying to create a super simple Low Battery alert monitor, by utilizing an open-loop comparator. LBO is active-low - it's connected to a TTL input pin of a uC, running from same Vbatt voltage. ...
5
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4answers
12k views

Detecting an open circuit by sensing current flow using a shunt and comparator

I need to detect if a load resistor is taken out of circuit. The load resistor is a photoresistor and can vary from 50k\$\Omega\$ up to 2M\$\Omega\$ and is driven by +5V to ground. The approach I ...
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3answers
1k views

Amplify .7Vpp square wave to 5Vpp square wave buffered to go over a 15-50 foot cable

I've got a sensor that outputs a .7Vpp square wave at 36kHz-60kHz. I need to take that square wave and amplify it to 5Vpp, as close to 0V to 5V rails as possible. Then I need to send that signal ...
1
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1answer
1k views

How to control squarewave oscillator with comparator output? (LM339)

I have LM339-based resistive water detector, which produces nice (almost) rail to rail output (see Schematics for device, which reacts to water?), and also LM339-based squarewave oscillator, taken ...
3
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1answer
257 views

Designing a latch with no constant power supply

I am trying to design a latch for an energy harvesting application with a very low power system. Basically I have a setup with a 3.3V regulated output driving a circuit, which is run off a capacitor ...
2
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3answers
502 views

Using an Op-amp as comparator

I have a dual op-amp that I want to use as a comparator: Vin should be compared to Vref (1/2 VCC). This is the circuit that I am using (as I have a dual op-amp, I am using a voltage follower on the ...
18
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5answers
26k views

Difference between differential op amp and comparator

What is the difference between a differential op amp and a comparator? I know a comparator can only give me two values (the supply values). The differential op amp amplifies the difference between ...
0
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1answer
2k views

Can't turn ON transistor from output of comparator?

I can't seem to turn on a 2n2222a with the output of a LM339 comparator, as soon as the base is connected to the output, directly or with a resistor, even if the output is 5 volts, 9 volts, I always ...
4
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3answers
923 views

Comparator - get the difference between inputs?

Is there any way to have a comparator (say LM339) output the difference between its +V and -V ?? For example, if +V is 6.3 volts and -V is 5 volts, how to get a 1.3 volts signal? Put another way, I ...
2
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3answers
4k views

Three Phase Input to Single Phase Output

We have three phase input and the voltages in the three input is not the same always. Sometimes, one or two or three phase will be off. I would like to connect the phase to output which lies within ...
0
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2answers
8k views

threshold problem on a Schmitt trigger op amp

I have the Schmitt trigger op amp on the below diagram. (channel A & B refers the oscilloscope probes on the following figures). The resistor values are selected to set the trigger threshold as ~...
2
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2answers
1k views

connection from an comparator to an optocoupler

I have the circuit below to decode a signal that is defined as Logic high >9.5 V and Logic low <6 V To determine the ...
0
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1answer
1k views

non-inverting schmitt trigger op amp - replacing a zener diode on the input

I wonder if it is possible to replace the second figure below with the first one? Would both Vo output be the same on the figures below? If they are different, ...
6
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1answer
4k views

Low power IR detector for microcontroller wake-up

I am working on an ultra low power infrared wake-up circuit for a microcontroller (Atmel XMEGA). I have IRDA comms working but the receiver uses too much current to keep on all the time. I need to run ...
1
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1answer
801 views

Magnitude comparator implementation

I have stuck on implementing magnitude comparator for 2-bit numbers (three functions - greater, equal, less). It is pretty easy to implement it with AND and OR gates, but the point is the task is to ...
4
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3answers
3k views

Help understanding BJT voltage comparator

I'm trying to understand how a transistor voltage comparator works. For example I've been studying this LM339: comparator circuit diagram http://lc.fie.umich.mx/~a0686696c/Materias_files/Lab.Elect....
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1answer
893 views

Problem with microphone powering up a comparator circuit

The circuit below is supposed to turn on a LED when the microphone input reaches these levels: 1V, 3V, 5V, 7V. What this circuit does in real life is when we turn on the power, all 4 LEDs light up. ...
0
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1answer
421 views

newbie: comparator adjustable level shift

I'm trying to build a simple fpga logic analyser and wondering how to best design the input circuit. I would like to support 8 channels, voltage between 0-5V, with a adjustable threshold range (lets ...
4
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4answers
13k views

Can you feed in a voltage higher than your supply to the input of an opamp?

I have a 28V digital signal. 28V being logic 1 and 0V being logic 0. Can I feed the 28V into an opamp (Vcc @5V) to level shift it ? Or will I have to create a voltage divider to bring the 28V < ...
6
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2answers
446 views

Issue with TI comparator

I'm having trouble with a comparator from TI (LMH7322). I use it in the circuit shown in the attached image "Comparator_1". Outputs go to an FPGA. The circuit is supposed to take a single ended input ...
2
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2answers
2k views

Techniques for analyzing Comparator circuits?

I'm looking for some general guidelines/equations I can use to analyze circuits which use comparators. In particular, I'm interested in hysteresis. For example, take the following open collector/...
3
votes
1answer
8k views

Generating sawtooth signal out of square/triangular signal

I want to create a sawtooth signal generator. I know, how to build op-amp comparator to create a square wave. I also know, how i can get triangular signal by integrating comparator output with op-amp ...
0
votes
1answer
770 views

USB ground on MSP430 Launchpad interfering with Comparator_A input voltage

I'm trying to read an audio signal from an Android phone as a serial input to an MSP430G2553, adapting this design to use the MSP430's onboard comparator module instead of an LM324. The Android code ...
2
votes
1answer
453 views

Op-Amp Comparator precision voltage

I need to trigger a speaker if my input voltage is higher than 0.6 V, otherwise the speaker must not be triggered. That's the reason I'm using an AMPOP Comparator: and, as far as I know, the voltage ...
3
votes
1answer
538 views

Role of current source in comparator

I have this schematic of a quarter of the internals of an LM339 from this site I want to know what the purpose of the four current sources are in this circuit, and how might they be implemented? I ...
0
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3answers
299 views

Comparators Dragging Each Other Down

I've assembled a circuit which uses RC timing compared to the voltage across a potentiometer. It is intended to run the motor in this fashion: ...
13
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5answers
8k views

Lengthening a 5 ns pulse

I have a 5 ns pulse width High coming out of a comparator that is asynchronous. I am attempting to count this pulse. My current microcontroller (dsPIC33FJ) has an asynchronous counter on board, ...
5
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1answer
3k views

Single supply op-amps in series

I have 2 op-amps in series, one is configured as an inverting AC amplifier and one as a voltage comparator. The purpose of this circuit is to detect a 4mV AC signal and trigger a transistor at the ...
2
votes
1answer
804 views

Use port for comparator and analog input?

I'm trying to use Port F on the PIC18F65J11 as both analog inputs and a comparator. For example, there are 7 pins on Port F, and I'd use 3 pins for comparator (2 comparator inputs, 1 comparator output)...
12
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2answers
5k views

comparator schematic symbol

This schematic appears in a recent question. The triangle may be an op-amp or a comparator, because they both have the same connections. (Why) isn't there a separate symbol for a comparator? The ...
2
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1answer
131 views

Does this setup create time distortion?

You have an RC element. After the RC element there is a comparator. After a given time of X minutes(X * 60 = R * C), the comparator reacts. Does voltage drop lead to time distortion, provided that ...
6
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2answers
973 views

Will this ADC circuit work as intended?

Here is revision 6 of the circuit. Hows it look? :) (This is an ohmmeter circuit. It measures resistances from 1 to 10M ohm with an accuracy of 1%. The resistor (not shown) is measured between J5 and ...
5
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2answers
10k views

What is the difference between a general comparator and a differential comparator?

I notice that the LM339 quad comparator comes in 2 different varietys: general-purpose and differential. Besides a big difference in price, what is the difference between the two? Specifically, I ...
4
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3answers
3k views

Help with a simple comparator circuit

I'm trying to build a simple temperature controller by using a thermistor and a potentiometer attached to a Schmidt trigger to control a relay. I realize that I have some serious design flaws in ...
6
votes
2answers
12k views

Comparator with hysteresis equations

I'm trying to be sure I'm computing the values for this circuit right. Here's an example of the circuit I'm trying to build (it's going in a 12 V DC system, so I filled that in already). I have ...
2
votes
1answer
1k views

Are there op amps or comparators that run on >100V?

I was using two op amps with inputs crossed as seen here: to make inverters for stepping up voltage with high efficiency. The design works well, but op amps seem to be only built for low voltages. I ...
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2answers
1k views

How to make an h bridge using only comparators

I discovered I could easily make an H-bridge (or something that effectively behaved as one) by cross coupling the inputs of two op amps. So for op amps 1 and 2, 1+ is connected to 2- and 1- is ...
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3answers
5k views

Need help driving N FET gate from LM393 comparator output

I am working on a charge controller circuit idea I had. The circuit 'works' meaning it achieved desired output voltage but the fet doesn't seem to be turning all the way on so lots of heat is ...
6
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2answers
1k views

How does this voltage comparator work?

Can somebody explain to me, how the following voltage comparator works? I believe to recognise U4A as an inverting Schmitt trigger, but how everything fits together escapes me... Should the ...
1
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5answers
1k views

Would this button trigger alarm circuit work?

This is a dead easy question for most of you! But I'm relatively new to circuit design, so I'd just like to ask whether this circuit might work (at all!) Here's a picture of the circuit Basically, ...
2
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2answers
303 views

OPAMP has voltage on its supply when it shouldn't

I was trying to design a circuit after seeing this question. I know I used too much components than I should designing a circuit with this purpose. And sorry about the messiness of the schematic. ...
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1answer
7k views

Comparator using Logic Gates only

How might a comparator with only logic gates look like? Isit like:
3
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1answer
479 views

Help breadboarding a circuit? [closed]

I've been building a light based alarm system, using an LDR, Op Amp, AND gate, some resistors, and an output of buzzers.. Here's my circuit so far... It beeps when it senses light as well as being '...
1
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1answer
332 views

A device which will detect a difference in voltage

A comparator can compare two voltages and output a signal indicating whether one is greater than the other. However, for balancing a lithium-polymer battery pack, I need to measure the difference ...