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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LTspice 101: Strange values with DC operating point

Just started using LTspice and I'm struggling with what is probably a total newbie mistake on a DC operating point test. Created a basic circuit, 10V voltage source and 1k resistor in series, and I'm ...
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1answer
77 views

Open-loop gain of Op-amp - LT6015

I was recently reading a technical article from AllAboutCircuits by Robert Keim about Op-amp Stability, http://www.allaboutcircuits.com/technical-articles/negative-feedback-part-8-analyzing-...
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1answer
42 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 ...
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1answer
67 views

A question about reactive power through a capacitor in LTspice

Before posing the question I would like to write the assumption I make for the power concept in passive circuits. As far as I know the power dissipated in an RLC circuit is the active power which is ...
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4answers
103 views

LTSpice common emitter amplifier distortion

I have a (hopefully not too trivial) question regarding this simple LTSpice-circuit. I would expect the output to be (ideally) a sine wave, but when probing Vout what I get is this: Now what I do ...
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77 views

LC Filter Response

I've been trying to replicate the step response of an LC filter in LTSpice but so far I haven't been successful. simulate this circuit – Schematic created using CircuitLab That is the ...
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2answers
61 views

How to define the initial charge of a capacitor in SPICE

I would like to simulate a circuit with a capaciot in LTSPICE. In the first hand, I have tried to charge the capacitors in a period of time. However, the charging current is very high and I am not ...
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2answers
32 views

LTspice default rising/falling times of pulse edges

Above is how I set up a pulse in LTspice. When I set the rising and falling edges as zero or if I do not register any value, in that case LTspice automatically sets the rising and falling edge ...
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33 views

bubba oscillator simulation not working

im trying to simulate an bubba oscillator circuit on LTspice but with no success, i get DC signal on my output, maybe im not using the suitable opamp(lt1013) ? i tried changing the values of the 2M ...
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1answer
93 views

Obtaining dynamic resistance of a zener diode in LTspice

Please left-click to enlarge Above is a circuit where: D1 is a 10V(breakdown) zener diode, V1 is a voltage source which varies from 11V to 5OV DC and R1 is a 1k resistor. My aim is to identify the ...
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1answer
58 views

Designing an High Amperage, Low Voltage AC Voltage “Breaker” for Model Train

I’m trying to build a simple circuit that acts as a "voltage breaker" – meaning that if a voltage exceeds a certain threshold, analogous to a (current) circuit breaker it will open a circuit. There ...
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2answers
47 views

Schmitt Trigger does not go to ground

i would like to create simple circuit to drive an computer fan (12V, 0.5A) is the temperature is above 42 celsius and stop when the temperature decreased below 36 celsius. I am simulating in LTSpice. ...
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3answers
135 views

Miscalculation of current for a pure inductive circuit in LTspice

A 10mH inductor is coupled to a 10V 60Hz AC supply as in the below circuit: Solution of the current amplitude for this pure inductive circuit is given as: But when I simulate this circuit in ...
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2answers
234 views

Using Spice/PSpice (Vishay optocoupler) models in LTSpice

I am trying to use the Vishay-provided spice models of the 6N137 high-speed optocoupler in LTSpice. (Source: http://www.vishay.com/optocouplers/list/product-84732/) Both the "PSpice" model and the "...
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1answer
54 views

Why Does LTSpice Always Show Negative Voltages in a Rectifier Circuit?

Rather new to electronics, I'm trying to design some of my first circuits. One of them includes a bridge rectifier feeding into an opamp used as a comparator. However, I'm a bit perplexed as to why ...
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2answers
40 views

high frequency noise from multiple feedback op amp

I've built a multiple-feedback low-pass filter with a TL084IN op amp. I've simulated the filter for the chosen R and C values using LTSpice and it looks like I was expecting: . I've also assembled ...
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0answers
29 views

How to generate PWM signal with low voltages using Schmitt trigger or linear circuits

I want to design PWL signal to drive this Mosfet so i need to generate PWL signal using Schmitt trigger circuit or using any oscillator. I have an idea about Schmitt trigger but as i implement in LT ...
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1answer
68 views

How to enter .subckt model in Ltspice?

This is a LTSpice model I created for a single electron transistor macro model: ...
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81 views

LTSpice divergence between AC analysis and transient analysis for low frequency gain

A simulation is done in LTSpice (version 4.23k) There is an inverter: Fig.1: schematic 1mV small-signal input. AC analysis is run. Low frequency gain (Vout/Vin) is 20.69 dB (10.82 times). ...
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1answer
104 views

Using a single phase induction motor equivalent circuit in LTspice

I was planning to simulate a circuit which will control a single phase induction motor in LTspice where mains is 230VAC 50Hz. In my previous question, I failed to find an example: Modelling a "...
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1answer
53 views

Modelling a “single-phase permanent split-capacitor motor” in LTspice

I'm planning to use an AC fan in an LTspice simulation. The AC fan is made up of a single-phase permanent split-capacitor (PSC) motor. Here is the actual fan: http://uk.rs-online.com/web/p/axial-fans/...
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1answer
59 views

Why this high-pass filter behaves like a low-pass filter for high frequencies, on this ideal LTSpice simulation?

I am simulating the usual active, first-order high-pass filter on LTSpice, as below: The Op-Amp I'm using is the following: This is the simulation result: What is the explanation for the ...
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1answer
57 views

Why Doesn't SPICE Show the Discharging of a Capacitor after Input Voltage is Removed

I have a very simple circuit that includes a capacitor meant to provide a few seconds of battery-like backup to a few LEDs when power is removed. In real life, it does exactly that. However, when I ...
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1answer
39 views

Narrow bandpass filter using maximally flat LPF prototype design

I'm doing a project involving wireless power transfer, where an LED will be turned on via 2 induction coils (tx and rx). The interfacing power circuitry for this has already been figured out (an ...
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45 views

LTSpice constraints on plots

A have a circuit for which I have parameterized some of its resistors with the .STEP command. Consequently, I have many different graphs when I simulate the circuit. I would like to know if it was ...
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1answer
30 views

What is the syntax for modelling a non-linear element in Spice?

Suppose I have the following circuit. My question is how do I write the net-list in LTSpice such that f(i) = i^2 + 2 (for example) ? I couldn't find the syntax on the internet.
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29 views

Simple Interconnect circuit to simulate crosstalk in ltspice

I want to implement a very simple interconnect circuit to simulate crosstalk in ltspice because I am new to this area of crosstalk. Where can I find such a design? I have searched in the net but all ...
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3answers
142 views

How can I implement a solid state relay in LTSpice?

I want a specified DC input voltage or above input voltage of a solid state relay to activate it. I want 3V or above DC input to turn on the relay's output switch. Here is the simple diagram: Is ...
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2answers
153 views

How do I simulate a dc-dc boost converter in LTspice?

For a electric circuits lab I had to implement a dc-dc boost converter circuit and take certain measurements while I varied the duty cycle of the pulse applied to the MOSFET so that I could observe ...
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1answer
34 views

Why LTspice is showing singular matrix error in the following inverter circuit?

While simulating this circuit I am getting an error of singular matrix. Any advice?
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1answer
31 views

bjt current biased in ltspice

For some reason when current biasing a very simple BJT common emitter circuit in ltspice, the current source needs to produce a massive amount of voltage. Why would this be? I'm biasing it at a Q ...
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60 views

LTSpice output looks very odd when I use LM7805

LM7805 output is supposed to be 5V but it's very irregular and it's close to zero. I also tried adding a series resistor to the power supply but it was no use. Also, it takes forever to complete the ...
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139 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 ...
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4answers
141 views

Is there a potentiometer model for LTspice?

I started designing a model for a three-terminal potentiometer in LTspice, since none are included and it's such a common component. Drawing the .asy symbol and the wiper terminal, it dawned on me ...
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2answers
92 views

add transistor model to LTspice

I'm trying to add the mmbt3904lt1g model to LTspice. - I've copied its data from the MMBT3904LT1.LIB.txt in the standard.bjt library. - I've added an NPN to my schematic then I've changed its value to ...
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2answers
118 views

LTSpice D flip-flop not working

I'm an absolute beginner with LTSpice; my first test circuit uses a few D flip-flops: four of them as clock dividers (to divide the clock frequency by 16), and then 3 as delay blocks (to delay the f/...
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0answers
18 views

Relabeling pin names of a model without replacing pin names

After downloading a model with pins only labeled as what seems to be hexadecimal numbers. I want to relabel the pin names. As the pin names contain integers, "find and replace" all pin appearances ...
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1answer
99 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 ...
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1answer
89 views

How to simulate a real inverter?

I'm new to digital electronics and I want to simulate in ltspice a circuit which contains a couple of 74LS04 inverters. What represents the "Test conditions" under the switching characteristics in the ...
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32 views

Half Wave Voltage Doubler Simulation stuck

I'm trying to simulate the following circuit on LTSpice simulate this circuit – Schematic created using CircuitLab The capacitors have 10Meg Parallel ...
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2answers
60 views

Demonstrating back EMF on an inductor in LTSpice

I'm trying to demonstrate back EMF on an inductor in LTSPice with this model: https://dl.dropboxusercontent.com/u/16979265/Draft2.asc I'm expecting the voltage on the inductor to have a negative ...
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3answers
103 views

What does a circuit's frequency response in dB refer to?

This is a simulated AC analysis of a small noise generating circuit. and comes from this circuit I have one of those fundamental but embarrassing beginners questions. What does the solid curve ...
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3answers
84 views

Input/output impedance of microcontroller

how to calculate the input and out put impedance for a micro controller , for the purpose of modeling in LT spice , for example RX610 family from Renesas For example the lumped characteristics can ...
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3answers
55 views

Why a DC coupled sine input signal will make my biased emitter follower looks like unbiased in LTspice?

I'm trying to simulate a biased emitter follower in LTspice. The dc operating point seems to be wrong once I used a DC coupled sine input signal(zero offset, 5V amplitude, 60Hz), it is almost 0V at ...
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4answers
84 views

High Pass filter gain at higher frequency than cutoff frequency

As i know , it's very common easy to find cutoff frequency and calculate gain at highpass filter. This is my circuit; simulate this circuit – Schematic created using CircuitLab My ...
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1answer
202 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 ...
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2answers
51 views

Issues with LTSpice Sallen-Key single-supply Simulation

I'm having trouble with simulating a Sallen-Key single-supply low pass filter using LTSpice. After fiddling around with the circuit for an hour I'm hoping for some assistance in troubleshooting. For ...
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1answer
28 views

Adafruit Anemometer

Recently I bought an anemometer from Adafruit. I was wondering is there is any way or approach which I can simulate the sensor for measuring the wind speed. If there is any software able to simulate ...
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1answer
81 views

Without C3 this Colpitts oscillator won't oscillate - why?

The pictured Colpitts oscillator circuit will not oscillate on a plug-in protoboard without C3 and its connection to ground in place. In LTSpice the circuit oscillates with or without C3 and its ...
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1answer
54 views

Are voltage transients on LTspice simulations significant?

I (incorrectly*) modeled this simple answer in LTspice IV and am seeing seemingly random instantenous voltage spikes up to +/-1kV on the output of the depletion nMOSFET. Are these real? If so, are ...