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Questions tagged [ltspice]

Anything related to LTSpice. LTspice is a SPICE simulation, schematic capture and waveform viewer program from Linear Technology. LTspice is freeware with very liberal license, it is lightweight and isn't crippled in any way.

41
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5answers
51k views

How do you simulate voltage noise with LTSpice?

Is there a way to setup a voltage supply with voltage jitter/noise? I want to experiment with filtering out noise on various voltages etc. but not sure how to configure LTSpice to create a noisy ...
24
votes
5answers
36k views

LTspice: Vary a resistor's value over time

I want to simulate the load regulation of a power-supply. I'm sure I remember being able to vary the value of a resistor over the course of a simulation in LTspice, but I can't remember how. Anyone?
14
votes
3answers
3k views

Why doesn't LTSpice predict this op-amp oscillation?

I'm developing a circuit to act as an electronic load for bench testing power supplies. An earlier question about how to test this circuit received several very useful answers and can be found here: ...
13
votes
3answers
14k views

Why is my simple boost converter giving me such a high peak output voltage?

I am trying to understand switch-mode power supply fundamentals through a simulation in LTSpice. I wanted to build an excruciatingly simple boost converter circuit following a teaching model often ...
13
votes
1answer
1k views

LTspice sinusoidal voltage source with offset much larger than amplitude broken?

I've been troubleshooting an analog circuit and have just come to the realization that Sine Voltage sources at mV are broken. Here is one that is supposed to provide a 1mV 1Hz sine wave on top of a ...
12
votes
1answer
7k views

How to plot “voltage drop” across a specific component in LTSpice?

In the above circuit I can only be able to plot |Vr1+Vc1| = V1 in green plot and Vc1 in blue plot. I use the voltage probe in LTSpice and click on the lines to obtain the plots. If I click on the line ...
11
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5answers
16k views

LTSpice Automation

I have a battery-powered boost converter and I'm attempting to measure the maximum input (battery) voltage droop under various load conditions of high current draws (different duty-cycles/...
11
votes
2answers
23k views

Why does LTSpice say that my “Matrix is singular” for this ideal-transformer circuit?

I'm trying to do find the voltage over R1 in the following circuit, where L1/L2 is an ideal transformer. LTSpice complains that the "Matrix is singular". Why? I've tried to play around with lots of ...
10
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1answer
683 views

Issue with parallel resistors in LTSpice

I'm trying to build a reactive load box, so I can run a guitar amplifier without a speaker. It's basically a device that simulates the impedance/frequency curve of a relatively high power speaker. I ...
9
votes
2answers
23k views

How to use .step param with more than two parameters in LTSpiceIV

I need to do three transient simulations with different values of certain resistors (conveniently called R1 and R2) in each. What I mean to do exactly is this: Sim. 1: R1 = 1 k\$\Omega\$, R2 = 10 k\$\...
9
votes
2answers
7k views

LTSpice simulation of rectifier slows down after short time

I have the following simple circuit set up in LTspice: Blue is on the output of the transformer and green from the rectifier. If I don't include a capacitor this works fine and the simulation goes ...
8
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3answers
8k views

How to view and customize beta of a transistor in LTspice

If I need to set beta to a custom value, is it possible to make a customized transistor with a beta of my choice? In other words, can I edit a ready or generic transistor's beta and save it as a ...
8
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3answers
973 views

What's the junk at the end of my FFT in LTSPICE?

Why do FFTs have junk on the high frequency end? Suppose I go to simulate this circuit in LTSPICE: simulate this circuit – Schematic created using CircuitLab Where the LTSPICE sine and ...
8
votes
1answer
5k views

How does the Arduino Deumilanove Auto-Reset Function work?

I'd like to hear some explanations as to how the Arduino Duemilanove resets the ATMega328P over USB through the FTDI FT232R transceiver. I know it involves the IDE playing some games with the DTR ...
8
votes
1answer
935 views

Has LTspice been extended to support the modified-Chan, non-linear hysteretic model for coupled inductors (transformers)

I'd like to figure out how to simulate coupled, non-linear cores using the included modified Chan model in LTspice and I'm specifically interested to know if LTspice has ever been extended to support ...
8
votes
1answer
2k views

LTspice: How can I show multiple probes with waveforms using stepping parameters in different colors?

I'm using LTspice IV (4.23I) and I am using the .step command to vary the capacitance of a capacitor, so that I can see multiple waveforms for a single probe. If ...
7
votes
2answers
2k views

How to control rise time of output of LTSpice's Voltage Controlled Switch?

I have a RC delay circuit as input into a Voltage Controlled Switch in LTSpice. It's working the way I want, except I can't figure out how to shorten the rise time of the signal that emerges from the ...
7
votes
1answer
250 views

LTSpice: What breaks KCL in .op but not in .tran simulation?

Simple BJT rheostat circuit, with a couple of resistors R1a and R1b representing the two parts of a potentiometer. Simulated in LTSpice IV using a part not suitable for this particular application and ...
7
votes
3answers
1k views

Discrete opamp design

I am working on modifying SG acoustics SGA-SOA-2 op-amp. The goal is to make it work on 32 \$ \Omega\$ headphones load, and use more common transistors. What I did was: Replaced all transistors ...
7
votes
1answer
546 views

N-MOS real-life gate threshold voltage (Vgsth) lower than claimed

I faced with a paradox that N-MOS transistor real-life Vgsth (gate-to-source threshold voltage) is significantly lower than claimed. It should be about 1.7 V (and the simulation confirming that ...
7
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0answers
4k views

Automate LT-SPICE? [duplicate]

I'm running a lot of simulations in LT-Spice, and I need someway to run them all either sequentially or at the same time. I was going to use Python, but I'm not entirely clear on how I would get ...
6
votes
1answer
2k views

How do I achieve XY mode on LTspice?

I have two node voltages that I wish to plot against each other, similar to the XY mode on an oscilloscope. How do I achieve this via LTspice? LTspice only plots quantities against time.
6
votes
3answers
5k views

How to plot sliding average in ltspice?

I would like to plot a sliding average of some voltages and currents. Ideally I would just add a new trace with some expression, but all expressions that I found so far only operate on single values. ...
6
votes
2answers
842 views

How can I link a component's current to variable resistor value in LTSPice?

In LTSpice I want to implement an LDR resistor which changes due to the current passing through an LED. I want the current through the LED (D1) to vary LDR. I want to use the LED's current in an ...
6
votes
2answers
7k views

Is there a spice directive to export waveform data in LTspice?

http://www.linear.com/solutions/1815 The above web-page explains how to export the waveform data to a text file. You basically run the LTspice simulation, clicking on the waveform window, go to ...
6
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1answer
1k views

How to change the top directory in LTspice?

I installed LTspice in C:\Program Files, and when I go to "search components", the top directory is C:\Documents. How can I ...
6
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1answer
755 views

How to change the temperature of sub-circuits in LTSPICE

I have subcircuits of a solar cell (resistors and diodes) in LTSPICE. I want to connect the solar cells (sub-circuits) together. However, each solar cell has a different temperature. I can set the ...
6
votes
1answer
6k views

Simulating real world transformer with LTSpice

I'm studying LTSpice, and I'm playing in transformer simulation. I want to modelize a real world power line transformer in a reasonable way: I mean I don't need an exact simulation of some specific ...
6
votes
1answer
14k views

LTSpice's ltline (lossy transmission line) symbol slowing down the simulation process. What can I do?

LTSpice has the element called Lossy transmission line (symbol name ltline): I tried to simalate a pretty simple schematic: R2,...
6
votes
1answer
5k views

LTSpice - Printing resultant parameters based on expressions

I'm designing a circuit but I'm computing the values of components based on a set of design values. For example, ...
6
votes
1answer
254 views

Simulating Chua's circuit in LTspice with a saturating transformer-based nonlinear resistor

Chua's circuit is one of the simplest circuits known to exhibit chaotic behavior. It consists of resistors, capacitors, an inductor, and an active nonlinear resistor. One implementation of this ...
6
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1answer
3k views

Unijunction transistor in LTspice?

I would like to simulate a simple oscillating circuit involving an unijunction transistor. I do not find such component in LTspice so I figure I need to import one. Could please show me step by step ...
6
votes
2answers
658 views

Op amp circuit stability in linear regulator circuit

I am trying to design a stable linear regulator using MOSFET and op amp. Schematics is shown below: I am using LTSpice for simulations. This circuit is mostly for educational purpose: I want to ...
6
votes
1answer
4k views

Using crystal in LTspice (where to get values for RCL)?

I'd like to simulate a schematic in LTspice driven by a crystal. An capacitor representing the crytal (as a resonant circuit) however it needs some specific values. Is there a table of common values ...
5
votes
2answers
444 views

Common source amplifier using mosfet: Why is my Id dependent on my Rd?

Since I'm (trying to work) in the saturation mode, the following formula should be valid: Since Vto is a static parameter it shouldn't change, same for K. And Vgs is 2 as determined by the voltage ...
5
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2answers
521 views

Charging one capacitor with another capacitor in LTspice

I'm trying to simulate charging of one capacitor \$C_2\$ by another \$C_1\$ using LTspice. Following the derivations in this video, I found that in the end, both capacitors \$C_1\$ and \$C_2\$ should ...
5
votes
2answers
3k views

LTSpice: How to vary resistances in a simulation depending on the value of a voltage?

I am trying to implement the Hodgkin-Huxley model for simulating neurons using LTSpice. One feature of this model is that the resistances at any given time actually depend on the transmembrane voltage ...
5
votes
1answer
5k views

SPDT in LTspice

I'm currently new to using LTspice as a circuit simulation software. Right now I'm trying to check if the IC (BD6221F-E2) that I included in the program is working. The process of making this IC is ...
5
votes
5answers
10k views

LTSpice (mac) How can I display the current in the schematic?

I want to simulate a circuit and display the current directly in the schematic. However I am only able to display the voltage. Here you can see an example where someone actually displayed the current ...
5
votes
1answer
5k views

DC power supply simulation trouble

I'm trying to simulate a relatively simple AC->DC power supply in LTSpice, but it's not quite cooperating with me. I've followed this schematic: only replacing potentiometers with resistors due to my ...
5
votes
2answers
1k views

LTSpice: Can I vary schematic temperature over time?

I'm trying to simulate a temperature sensing schematic with a latching function (meaning that the schematic should go to overtemperature mode at let's say 75C and go back to normal at 50). I can do a ...
5
votes
2answers
6k views

Adding Photodiode to LTspice

I am very new to LTspice. I would like to ask "How can I add a photodiode in the Ltspice?" Is ideal photodiode (or any specific) model already included in the LTspice or do I need to create third ...
5
votes
2answers
14k views

“Unknown subcircuit” in LTSpiceXVII

I'm attempting to simulate a circuit that is intended to take a 5V/GND input and make split +/- 2.5V rails with a virtual ground. When I try to simulate, LTSpice complains about "unknown subcircuit" ...
5
votes
2answers
487 views

How to break components in SPICE?

I've been learning SPICE over the past few days, using the LTSPICE program. One thing that just escapes me, is how exactly do we know when a component's absolute maximum ratings have been exceeded? ...
5
votes
1answer
6k views

LTspice: Vary a capacitor's value over time

I want to vary a capacitor's value over time. A previous question (LTspice: Vary a resistor's value over time) asked how to vary a resistor's value over time. One of the answers was to use a ...
5
votes
1answer
1k views

How to model a noisy Zener diode in LTSPICE?

I'm trying to simulate a white noise generator of the Zener diode style. I'm going with current amplification, rather than the more traditional voltage amplification just because. My problem is that ...
5
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2answers
8k views

Parts tolerance simulations in ltspice

I just recently found this tutorial (and various other places mentioning a similar technique) when trying to evaluate how one of my circuits behaves when using real world components with real world ...
4
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1answer
2k views

Why am I getting negative base current in LTSpice simulation?

When I was trying to bias an NPN transistor I noticed that the base current Ib is negative in LTSpice. So for the sake of simplicity I only apply voltage to the base-emitter junction. As you see in ...
4
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3answers
2k views

LTspice gives wrong AC analysis

I have multiple issues with LTspice. Take this trivial example: ...
4
votes
2answers
441 views

LTSpice transistor output capacitor not decoupling DC

The circuit below shows a Darlington pair that is used to amplify an AM signal picked up by an LC tank. As you can see in the input and output waveforms below, the signal is amplified but not ...