Welcome, Guest. Please login or register. Did you miss your activation email? This topic This board Entire forum Google Bing. Ensuring 0V output? Print Search. Author Topic: Help with comparator in LTspice? Read times. Trying to build a simple comparator based on the LT in LTspice that will output an arbitrary voltage in this case, 0.
The comparator seems to pull up the voltage fine, but when the input is above the threshold it appears to output about mv in the simulation. Is there a simple way of pulling this down as close to 0V as possible? M Super Contributor Posts: What do you expect from a comparator with a BJT open collector output?
The following users thanked this post: bluebreak. What are you actually doing? For example, if this is a reference voltage for another circuit, consider using analog switches don't forget to include their resistance! Bringing a project to life? Send me a message! So analog switch mosfet driven from the comparator is a better way to go? Quote from: floobydust on October 10,am.
Zero Super Contributor Posts: Country: Quote from: bluebreak on October 10,am. Quote from: Hero on October 10,am. So that's fine. I think you will need to add hysteresis to the circuit. Any slow moving waveform can make the comparator output chatter. Simulations don't show this, so when you build the circuit you may find it oscillates near the 5.
Take a look at this circuit Very nice Hugo Are those transient peaks I see from lack of a hysterisis loop in the circuit or could those just be smoothed out with a filter cap? Otherwise it looks excellent for my usage.Tight offset voltage specifications and high gain allow the LT to be used in precision applications. Matched complementary outputs further extend the versatility of this comparator.
Quiescent negative power supply current is only 3mA. This allows the negative supply pin to be driven from virtually any supply voltage with a simple resistive divider. Device performance is not affected by variations in negative supply voltage.
Analog Devices offers a wide range of comparators in addition to the LT that address different applications. At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist. ADI has always placed the highest emphasis on delivering products that meet the maximum levels of quality and reliability.
We achieve this by incorporating quality and reliability checks in every scope of product and process design, and in the manufacturing process as well.
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If you haven't already been through the Getting Started with LTSpice guide, you should definitely wait as an update to the audio quality is desperately needed.
For those of you who watched it and finished it - bless you. I'd thought I'd kill two birds with one stone here and continue the LTSpice tutorial with an introduction to operational amplifiers -- or op amp for short. We will be covering just the basics here - what are op amps, some common configurations, and a couple examples - and we'll end with a nice, simple project to hopefully get you inspired to work with analog circuits a bit more.
An op amp is a voltage amplifying device. With the help of some external components, an op amp, which is an active circuit element, can perform mathematical operations such as addition, subtraction, multiplication, division, differentiation and integration. If we look at a general op amp package innards to come in a later tutorial such as the ubiquitouswe'll notice a standard 8-pin DIP dual in-line package :.How to protect circuits from reversed voltage polarity!
Photo courtesy of Learning About Electronics. We are mainly concerned with five of the pins. The circuit symbol for an op amp is a triangle with five pins shown below. An op amp has a wide range of uses and, depending how each pin is connected, the resulting circuit can be some of the following this is by no means a comprehensive list :.Simple moving average method of forecasting
Throughout this tutorial I will show you how to measure typical op amp characteristics such as gain, bandwidth, error, slew-rate, current draw, output swing and other characteristics found on device data sheets. The op amp is designed to detect the difference in voltage applied at the input the plus v2 and the minus v1 terminals, or pins 2 and 3 of the op amp package.
The difference is also known as the differential input voltage. The output, then, is the difference sensed at the input multiplied by some value A - the open-loop gain. An op amp behaves as a voltage-controlled voltage source, which we will model now.
We will simulate both an open-loop and a closed-loop amplifier configuration. Since the output resistance Rout is zero, there is no voltage loss at the output. The diamond-shaped voltage source in the image above is known as voltage-dependent voltage source, and in this case the voltage is the gain G multiplied by the difference between the input terminals Vin.
The gain is normally referred to as A in texts, so the equation for the output is given by:. Let's model a voltage-controlled voltage source and see if we can't get its behavior to mimic an ideal op amp. Op amps are not meant to be used as stand-alone devices. We simply verified the Vout equation in the ideal op amp video to show why it is commonly referred to as a voltage-controlled voltage source. We are going to talk about feedback and closed-loop gain and application.
What is feedback? Feedback occurs when the output of a system is fed back into as input s.
LTSpice model for LM393
There are two types of feedback: positive regenerative and negative degenerative. Feedback is applied to the system to affect one or more of the following properties:. When were talking about gain, we are taking the ratio of the output to the input. In the.
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LTspice quad comparator
Viewed times. I think I haven't wired the LT right.Telegramfxcopier io
Do I have to do anything with the "B" and "S" pins? I am open to using another part for the comparator as long as it is available in LTSpice. Neil Dey Neil Dey 2 2 silver badges 7 7 bronze badges. Active Oldest Votes. Spehro Pefhany Spehro Pefhany k 9 9 gold badges silver badges bronze badges. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. Podcast Programming tutorials can be a real drag.Latest Projects Education.
First I tried to use a general opamp2 and insert the subcircuit model but I got error about missing nodes. I assume that was because the model is for 4 comparators together. Then I tried to automatically generate the model Right clik- 'Create Symbol' but the program shows an error regarding permission.
I changed the restrictions at the C file for LTspice without any result. Is there a way to use a single comparator with the same performance of LM For instance, can I modify the model to account for a single comparator?
Thanks for any idea. Scroll to continue with content. I copied the subckt def from your post and placed it in a text file. Usually there is just one opamp definition in the subcircuit file. If you want four, just insert or copy the first instance three more times.
Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. It only takes a minute to sign up. For fast simulations I sometimes need an ideal comparator.
I guess it is not a built-in component. How can it be implemented by ideal sources or VCVS ect.? While not disregarding user's answer it is a valid oneI have to warn you that behavioural sources, while versatile in terms of mathematical expressions, tend to suffer from limited dynamic range and slower simulation speed when higher numbers are involved.Maxiflash jvci
If your application does not involve great dynamic ranges on both y and x axesor high values to be processed say hundreds, or kV, upwardsthen behavioural sources are just fine. Else, you should know there is an A-device in [Digital] : the Schmitt trigger. If your reference is a fixed voltage, that doesn't change during the simulation, you can use the single input with the internal parameter vt set to the reference voltage.
If not, use whichever input you want, or need, for the variable reference voltage. Another way is to use the table function with a VCVS or a VCCS, thought the latter is preferable due to it being recommended by the manual as being convergent-friendly, compared to its voltage cousin. This component looks like an open switch OFF when the differential input voltage is greater than the threshold Vt and like a closed switch ON when the input is less than the threshold.
So if Vt is set to 0 volts and the negative terminal of the output is tied to ground the SW component will act as an ideal comparator with an open drain output. The SW component also allows you to specify a hysteresis value for the input.
Another way would be to use an ideal op-amp as shown below, but flip the terminals around and ditch the gain :. Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. How can I make an ideal comparator in LTspice? Ask Question. Asked 2 years, 6 months ago.
Active 10 months ago. Viewed 9k times. LTspice is usually for real world circuits. I use a digital buffer or schmitt trigger for simulating a comparator.How to disable auto adjust on dell monitor
Can you write that schmitt ot digital buffer way as answer with a small example? There are examples. There are probably better ways around it, but I use e to scale down signals to the V level the ideal digital support, and then e on the output to scale up in voltage again to your Vcc.
Active Oldest Votes.The challenge sounds simple enough - take a 60 Hz or 50 Hz sinewave from the AC power line and convert it to a square wave. This signal will serve as a clock to drive counters for a 24 hour time clock. So you hook up an op amp as a comparator to do the job. But your surprised to see the clock running too fast!
With oscilloscope in hand you discover the AC line is noisy! And to your horror, you see glitches additional edges at the comparator's output, causing the counters to advance too quickly. What you need is a better comparator, immune to the noise swinging above and below the comparator's threshold. What happens at the output? Plot the input V 2 and output V 6. It appears the comparator performs well as a zero-crossing detector and all is right with the world.
However, the real world throws in a few "goodies" for free - mostly noise where you need it the least. Rerun the simulation and let's look at our output now. Unfortunately, our fine square wave is rife chatter - it no longer provides one rising edge per 60 Hz cycle! How do we overcome the problems of the basic comparator?
Introduction to Operational Amplifiers with LTSpice
Just add some positive feedback to the circuit. What are these two thresholds? Some simple math uncovers the answer. The only tricky part lies in the fact that one of the variables, Vo, can be in one of two states:. We get two thresholds for VIN:. Having two thresholds based on both the input VIN and the current output state is called hysteresis.
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