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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.

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MOSFET output voltage vs. gate voltage

I don't understand why I am getting this behavior from my MOSFET circuit. Either because I'm not using LTSpice correctly, or I'm not understanding MOSFETs. I set up the voltage to the gate to be a ...
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17 views

Integral in mathematical expression of capacitor/resistor LTSpice

I know how to simulate a variable resistor in LTSpice. For example for a heating resistance the equation can be made by considering heating equation and can be expressed like R=(Ri-Ao*EXP(-time/To)) ...
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34 views

How can I export the frequency response from LTSPICE without phase wrapping?

After I plotted the frequency response of a circuit using LTSpice as shown: I exported the plots data as a .txt file in order to plot them after that using MATLAB, however, after I plotted the data ...
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35 views

LTspice stacks data points on the same vector when I do linear parameter sweep

I am trying to export the voltage of a transformer for different mutual coupling values. However, when I do a linear increase of mutual coupling it seems that LTspice will stack the parameters in one ...
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Wrong frequency response - LTSpice

So I have this simple OP-AMP circuit that is supposed to be a low-pass filter for which I made the calculations so it passes all frequencies below 1591 Hz (approx). The values of the components are in ...
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2answers
43 views

Ideal LC circuit decays over time in LTspice

I was trying to simulate a transformer without a load, and setting an initial condition to observe how the energy will flow from the primary to the secondary circuit. I realized that the energy will ...
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55 views

opamp constant-gm bias circuit

I try to incorporate the constant-gm bias circuit (Figure 6 in Improvements_in_biasing_and_compensation_of_CMOS_opamp) into the PFC (positive feedback frequency compensation) opamp, but it resulted in ...
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57 views

LTSpice: Produce Bode Plot for Compensated & Uncompensated Boost Converter

I am designing a product which uses the LTC3122 as a 5V-12V boost converter (datasheet here). This particular device provides the ability to add gain compensation, phase lead, or both. In my case I am ...
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56 views

Some LTspice questions. Decoupling capacitor doesn't effectively block DC. Pull up resistor voltage doesn't drop to logic low level

I'm trying to design an interfacing board that is used between a micro-controller and a phone simulator (a picture of the schematics is attached). The 44VDC is used for the phone simulator to detect ...
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28 views

Estimate Phase Margin in Spice

I am trying to determine the phase margin of my design and I have come across two methods for modeling the open loop gain in spice. The problem is they are yielding slightly different results. I have ...
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49 views

Sinusoidal voltage source not being sinusoidal in LTSpice

I'm trying to obtain the output resistance (resistance from collector node) of the following circuit By inspection, it should be the output resistance of a common emitter amplifier with degeneration ...
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49 views

opamp simulation

Is the following open loop transient simulation of opamp correct ?
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LTspice : using a sqrt(-1) in behavioral model

i would like to simulate an equal circuit of two coupled inductors, So i need a behavioral voltage with following expressions: V=jwI(R2) LT spice do not recognize sqrt(-1), any idea for simulating ...
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57 views

Magnet Shake Generator - how to replicate in LTspice?

I made a generator for my wife's 3rd grade class, since they are learning about magnets, electromagnets and electricity. It's a simple pipe with a stack of magnets inside and you shake it to produce ...
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1answer
59 views

LT spice: change amplitude of a voltage source over time in LTspice

I would like to have a sinusoidal voltage source that varies over time, for example; for time duration 1msec : 3v 13.56MHz for time duration 2msec : 10v 13.56MHz please help. i studied Help for ...
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1answer
42 views

How to implement AC analysis in a resonant circuit in LTspice

In previous LTspice simulations, I've set the AC amplitude of the voltage source to 1 and then carried on with the .ac spice directive. How do I setup the AC analysis for this circuit? Do I set the ...
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46 views

Function generator design

So i was asked to design a function generator that eventually produces a sine wave at the output of the circuit and this is what i have come up with so far. A Schmitt trigger and then an integrator ...
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What is this circuit component called, and how do I find it in LT Spice [closed]

Hey guys I'm pretty new to Schematic drawing and I was just wondering what this kind of part is and where I could find it in LT Spice. Thanks for the help.
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75 views

Buffer output of operational amplifier

I'd like to buffer the output of an operational amplifier using a source follower. The operational amplifier produces a sinusoidal wave like this. I would like to buffer this signal. To do that I ...
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20 views

enveloping curve - LTPSICE

I have built a simple rlc circuit with a pulse input and performing transient analysis on it. I am interested in the voltage of the behavioral voltage source as shown in circuit. The system is an ...
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34 views

LTSpice PWM Signal Showing Capacitor isn't Fully Discharged

I'd like to create a pwm signal input to mimic a real life situation of a pwm input that shows the capacitors aren't fully discharged. Please see the image below. I am currently able to create the pwm ...
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47 views

analogous mechanical electrical system- LTSPICE

I have created a basic series and parallel rlc circuit in LTPSICE. According to this http://lpsa.swarthmore.edu/Analogs/ElectricalMechanicalAnalogs.html and https://www.tutorialspoint.com/...
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69 views

If I need to find an MOSFET spice model with a particular length and width, where do I start?

I was using a 180nm NMOS and PMOS but now need to use an NMOS with about L=.36u and W=100u. I have two models but I dont think I can just change the length and width to any value. How can I check if ...
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66 views

LTSpice current dependent current source timestep too small error

I solved this circuit by hand.Which asks to calculate vo and Io in the circuit. And I tried to verify results with LTSpice. If I change dependent current source B2's equation to I = I(R1)* 50 it ...
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Correctly Using the Chan model in LTSpice

I am trying to use the Chan model to better simulate a transformer in my design. When I am making an equivalent transformer circuit, where does the Chan inductor go? On the LTWiki it is implied ...
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LTSpice: How to start the step of a voltage source at a different time in the transient simulation than t=0s?

If I have a complex circuit where things occur at different times instead of starting as soon as the simulation starts (t=0s), how do I setup those things to occur at different times in the simulation....
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This SR latch built with 180nm CMOS does not work in ltspice. How do I fix its behavior and parameters?

EDIT: I copied over the latch from another larger model that had Vdd defined, but missed it when copying over the design. However, after adding in Vdd, I still run into this confusing issue where the ...
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1answer
79 views

IF statement on LTspice

I would like to create a variable resistor as following: R2=1 if i(R2)<1 R2=2 if 1<i(R2)<10 R2=3 if i(R2)>10 I know that the syntax is: ...
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35 views

Time varying function on LTspice

I would like to create a variable resistor as shown in the attached pictures. How can I create this function? I saw the following tutorial, but I don't know hot to replicate my function (where some ...
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1answer
49 views

Current through a diode changes for the same forward voltage in two circuits

In LTspice IV, I am simulating a 1N914 diode behavior in response to a variable current source in two circuits. One circuit has just the current source and the diode, and the other has the current ...
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1answer
65 views

LTspice 60 Hz notch filter simulation

I am trying to build an EEG circuit based on the description here: https://www.instructables.com/id/DIY-EEG-and-ECG-Circuit/. I would like to simulate the behavior of certain sections of the circuit ...
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58 views

Using LTSPice to make Function Blocks for SIMULINK

I have a PLL that I want to model in Simulink using the control theory toolkit. I have the schematics for the PLL in LTSpice. Does anyone know of a way that I can integrate the spice model with my ...
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LTSpice: How to offset the start time in a transient simulation?

I see how to set the total run time for a transient simulation, but what if I didn't want the simulation to start at 0s? For example, if I have two voltages sources that are stepping at offset times ...
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LTSpice: When running a linear AC simulation, how to view the voltage ratio between two voltages?

For example, how would I see the ratio between Vi and Vo for a linear AC simulation?
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How to add thermal model on SOAtherm-Nmos block in LTspice

I would like to analyze the junction temperature of a SCT3022AL MOSFET during switching operation on LTspice. Followint the Spice model and the thermal model of the MOSFET: https://www.rohm.com/...
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91 views

Adding a second Y axis to an LTSpice plot

I am new to using LTSpice and am coming over from using Cadence. In Cadence you can add a second Y axis. Plot-> Add Y Axis is the probe pane in Cadence. Is there a way to do this in LTSpice?
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94 views

NPN Transistor common emitter calculation

I built the following circuit in LTSpice using the default NPN BJT model (beta = 100). I calculated the Ib to be 115.754uA. This is how I did the calculation: Equivalent voltage at base is: ...
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78 views

LTSPICE Simple MOS-FET Stacked Current Mirror/Cascode saturation threshold less than expected

I am running a few very rudimentary cmos circuits in LTSPICE. For some reason, when designing stacked mirrors, I seem to get a much lower saturation turn on thresholds would be expected. I've tried ...
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ltspice: simple nmos circuit

I built up a circuit which did not work as expected. I reduced the problem to this circuit: I expect to have a current of ~2.4 A at gate voltages below 10 V, but actually the transistor does not ...
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Model of Mosfet Switching in LTspice

I would like to perform a simulation on LTspice about a switching MOSFETs. In particular on how the parasitic inductance and capacitance affect the switching transient. In order to perform this ...
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Can't achieve the goals in designing and simulating Resonator circuit

Goals I need to design resonant parallel circuit and simulate it with LTSpice so that it match with the design requirements correctly. Requirements Source Impedance \$R_s = 100\ \Omega\$ Load ...
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58 views

D-Class Amplifier Design Verification

I have an internship coming up working with comparators and amplifiers, so I wanted to take on a side project involving both of those components. Designing a D-Class amplifier seemed like a great way ...
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84 views

LM317 maximum current output as a voltage regulator

I built the following circuit in LTSpice using LM317. With a current load at the output, stepping from 0.1A to 1A, I noticed the output voltage collapsed at around 800mA. This is a surprise, since I ...
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Slope of the Inductor current

this forum is very helpful in the term of power-electronics. I got a question about LT-spice simulation. I want to compare the slope of the inductor current in two circuits.The only difference between ...
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1answer
46 views

Custom photodiode symbol in LTSpice 'syntax error in transmission line statement: “..”'

I want to simulate different opamps for use in the transimpedance amplification stage in a position sensing device (PSD) photodiode. The equivalent circuit for the PSD photodiode is saved in ...
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1answer
98 views

Lt-spice switch model

I have a very simple circuit and want to see the current in the inductor. But I do not know why switch is behaving like that... Actually, I supposed to get KA range current. but it gives me very ...
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1answer
69 views

Creating a temperature-dependent solar cell in LTSpice (using varistors)

I'm currently working on my master thesis and therefore need to simulate a solar cell in LTSpice. I've already modeled and simulated some examples with constant values. But for a more accurate model, ...
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1answer
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LTSpice: active load current generator soft saturation

I would like to use a current generator to pull down the voltage to zero (there is a voltage generator with a series resistor). The current generator models the output of a specific circuit, so it is ...
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51 views

Best place to report an LTSpice XVII crasher?

I have a small LTspice XV11 .asc file that reliably gives a SIGSEGV when I run the simulator under macOS 10.14.3 (Mojave). This is related to LTSpice IV for OS X (oct 2, 2018 version) crashes on ...
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Plot voltage for different resistor values in LTSpice

I've signed up for a SPICE course at work, that will take place on Monday and I'm desperately trying to learn electronics and SPICE. (I work as an embedded engineer but with very lacking electronics ...