Please submit your requests for additions or changes to Undocumented LTspice on the "discussion" page second tab above. Because of its superior performance, excellent community support and ease of file sharing, it is rapidly replacing all other SPICE programs, regardless of price, as the simulator of choice for hobbyists, students and professionals alike. The purpose of this topic is to explore and explain some of the many useful or quirky features that have never appeared in the standard documentation whether due to simple oversight, the feature being considered not important enough, not polished enough or functionally obsolete — or even due to the feature being considered proprietary to another brand of SPICE or to LTspice itself.
LTC considers some of these undocumented features as fair game for open discussion in public forums such as the LTspice Yahoo users group, whereas for others, it considers any such open discussions as a violation of its License Agreement. Such items are all considered as having been officially " documented " and are specifically allowed as discussion topics in public forums such as the LTspice Yahoo users group.
However, be advised that any items that have been dropped from the documentation, even if still functional, should generally be considered obsolete and in risk of being purged from the program code at any time fortunately, such items are quite rare. As to the classification of anything not covered above, you must make your own common sense judgment or ask the advice of the users group moderator or the program author via private email.LTSpice Tutorial - EP1 Getting started
A lot of the standard devices have undocumented parameters e. For these reasons, this last category of undocumented features will not be directly discussed here. LTspice generally represents numbers using 64 bit double precision arithmetic with the following data structure:. However, because of the 52 bit precision of the fractional part of the significand, the practical numerical dynamic range will be circuit dependent. A 53 bit binary significand gives LTspice about 16 significant figures for internal math computations.
Thus, if impedances vary by more than 16 orders of magnitude, numerical difficulties may ensue, depending on the topology of the circuit this is because matrix solving frequently involves differencing two very similar numbers — for example, the next larger number than one is 1. LTspice's proprietary alternate solver extends this precision by about another 3 orders of magnitude at a cost of a modest speed penalty. Note that all A-devices have up to 8 possible active device connections, up to 5 inputs terminals 1 through 5 usually 2 outputs terminals 6 and 7and with terminal 8 always as the device common.
A-devices are always netlisted with the full eight connections. The netlister connects any unused inputs and outputs to terminal 8. The A-device compiler recognizes this condition as a flag that that terminal is not used and removes it from the simulation matrix.
A-devices are implemented this way to allow a single device type to act as any combination of a 1 to 5 input, 1 to 2 output device, but with no simulation speed penalty for unused terminals. Not documented anywhere by LTCbut the first two of these devices were extensively documented in the users group. The behavioral a-device Sample and Hold has two modes of operation. Note that one and only one of these two inputs must be connected. The default transfer function is a hyperbolic tangent tanhwhich closely approximates the transfer function of a bipolar transistor differential amplifier this limit can be disabled by adding the flag parameter, Linear.
The transconductance current source output appears on pin 7. As usual, pin 8, if connected, becomes the device's floating "gnd" reference. For reference, a dc "rail" voltage, which represents the maximum possible output calculated from combining both voltage and current saturation limitsappears on pin 6.
This voltage reflects the negative limit only and has an output impedance identical to that of the main output.This LDR circuit diagram shows how you can make a light detector. Here is the schematic for the circuit:. They are made of high resistance semiconductor material. When light hits the device, the photons give electrons energy.
This makes them jump into the conductive band and thereby conduct electricity. Check out Wikipedia for the physics stuff. This makes the voltage at the base of the transistor too low to turn the transistor ON. Therefore, no current will go from the collector to the emitter of the transistor. All the current will instead pass through the LDR and the potentiometer.
This makes the voltage at the base of the transistor higher. High enough to turn the transistor ON. Because the transistor is turned on, current flows through the transistor. It flows from the positive battery terminal, through R1, the LED, and the transistor down to the negative battery terminal. The resistor R1 controls the amount of current going through the LED.
I have written an article on how to calculate the resistor value for an LED. What if you want to power the circuit with something other than a 9V battery? Then you need to change the resistor value to get the right amount of current flowing through the LED. The variable resistor R2 is used to change the trigger point for the LED. You can probably get away with a 10k potentiometer. It depends on the resistance of your LDR.That is what I do when simulating LDR type componets.
I just use the potentiometer as a substitute because basically that is all a LDR is. United States. Multisim and Ultiboard. Turn on suggestions. Auto-suggest helps you quickly narrow down your search results by suggesting possible matches as you type.
Showing results for. Search instead for. Did you mean:. LDR Component. So, Can someone help me finding that? Message 1 of Re: LDR Component. Active Participant. Signature: Looking for a footprint, component, model? Message 2 of When i use the component you said in your reply, i got an error: "unknown device type"!! And, How can i create my own part? Message 3 of Message 4 of Message 5 of Message 6 of Message 7 of I am going to post a circuit for you to examine.
It is your circuit with a few modifications to possibly simulate your LDR. This is not going to be exact but a close approximation of how an LDR would work. I will give an explaination below. Feel free to modify it to suit your application or need. Used an opto coupler to simulate a light source and receiver. I added a pot to the collector of the photo trasistor to simulate the varying nature of the actual LDR.Included in the download of LTspice are macromodels for a majority of Analog Devices switching regulators, amplifiers, as well as a library of devices for general circuit simulation.
Contact Technical Support for assistance.
Our enhancements to SPICE have made simulating switching regulators extremely fast compared to normal SPICE simulators, allowing the user to view waveforms for most switching regulators in just a few minutes.
This video provides an overview of the advantages of using LTspice in an analog circuit design and how easy it is to get started. Download for Mac View More. Additional support for LTspice can be found within our documentation, including keyboard shortcuts and a visual guide. Our extensive collection of technical resources tackles a wide range of LTspice topics, like keyboard shortcuts, evaluating electrical quantities, and parametric plots. Documentation Additional support for LTspice can be found within our documentation, including keyboard shortcuts and a visual guide.
LTSpice IV help with variable resistor
Latest Resources.Some of the most common waveforms needed in simulating voltage and current sources are sine, square, triangular and sawtooth shapes. PULSE fuction is often used in transient circuit simulation where we want the source to behave like a square wave. You can omit Ncycles if you need a free-running square waveform. A simple approach to creating a triangular and sawtooth waveform is using the PULSE fuction using the source component editor shown above.
Likewise, to create a sawtooth fuction you cab set the rise time equal to the period and the fall time to zero.
Adding Spice Models to LTspice
Waveforms for these two fuctions are show on the top of the page. For any arbitrary or complex waveform, you can always rely on the piece-wise linear function. The arbitrary piece-wise linear fuction is defined by a sequence of time and voltage pairs.
PWL t1 v1 t2 v2 t3 v This specifies that for time before t1, the voltage is v1. For times between t1 and t2, the voltage varies linearly between v1 and v2. There can be any number of time, voltage points given and for times after the last time, the voltage is the last voltage. To implement a triangular or sawtooth waveform you could use the following piece-wise linear functions.
These two examples use an undocumented repeat feature of PWL function. To explore these features you will need to directly edit by right-clicking on the source symbol's text in the schematic editor rather than using the source component editor.
PWL 0 0. More information on the pulse, sine, exponential, single frequency FM and an arbitrary piece-wise linear functions is available in the LTspice help file F1.
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It only takes a minute to sign up. I am very new to LTspice. I would like to ask "How can I add a photodiode in the Ltspice? If it is already includedunder with categories it is included in library? Or If it is not includedhow can I make one? Do I need to create the spice model of photodiode which will consist roughly of a current source, capacitor and resistor then refer back to the photodiode?
Or if there is another way around can you please share your knowledge? The easiest way to get a photodiode, and to control itis to use one of the built-in optocouplers. Another way is to find a photodiode model on the internet as the.
You can add such a model directly to the diagram and connect it under the diode symbol. Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. Asked 3 years, 9 months ago. Active 1 year, 5 months ago. Viewed 9k times. Sui Sui 2 2 silver badges 5 5 bronze badges. I see. So I can use a current source may be in parallel with capacitor instead of photodiode? Active Oldest Votes.
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This tutorial is going to cover adding custom Spice models into your LTspice simulations and library. While it is very easy once you know how to do it, there are a couple pitfalls that nearly caused me to go crazy and rip my hair out in the past.
Hopefully this will save you some time and stress, and possibly a hole in your monitor. It might seem obvious, but the first thing you need to do is find a suitable Spice model. This can usually be done in one of two ways. An unfortunate characteristic of the Spice world is that over time it has become fairly fragmented. Different design tools use different versions of Spice, hence, part manufacturers will often have the Spice file for their part available in a couple different formats.
The best format to use is the Spice3 model, however the PSpice model will usually work in LTspice as well. Once you have found the model you want to use, you need to make sure it is in the correct format with the correct extension. A Spice model file is nothing more than a text file with a different extension. In the case of LTspice, if the model file contains only a single model, it should be named with the.
If the file contains multiple models, then the file should be named with the. Where you type the file name in the file name text box, type the exactly desired file name in quotes, and the program will name it exactly that.
For example you could type 1N If you tried typing the file name without the quotes you would get 1N For this tutorial we will be using a Spice model for a made up diode called the 1NADAMnamed after your beloved engineer, me! MODEL statements.
Most Spice models downloaded from the internet will have. MODEL statement will not sufficiently model the complex behavior of modern parts.
I am assuming that the reader knows the difference between a. MODEL explaining those thoroughly is a topic for another tutorial. In short, however, a. MODEL statements will work for simple simulations and old parts, it will not be very accurate for newer, smaller parts. For example, transistors have become so small and non-ideal, that the equations which we all learned in textbooks do not provide sufficient accuracy for good simulation results.
This is one case where a.
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