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Installing and using LTspice IV (now including LTXVII). From beginner to advanced.
Installing and using LTspice IV (now including LTXVII). From beginner to advanced.
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Old 19th August 2021, 08:24 PM   #3051
kees52 is offline kees52  Netherlands
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Hi All

I have found after help from a Gan manufacturer how it is done with the flying cap buck. I was close all the way but did not see it, the need of separate drivers, so she use just High side of the gate driver for the above mosfets, and so I have level shifted the right way, have to say, it looks strange.

Only I need a way to get flying capacitor C2 to his working voltage without to wait very long when simulating, can I make a setup with C2 so it is on the desired charged voltage so I can see how it does?.

thanks.
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Last edited by kees52; 19th August 2021 at 08:26 PM.
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Old 19th August 2021, 10:23 PM   #3052
jan.didden is offline jan.didden  Europe
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Kees you can set the node voltages to anything you like at simulation start.
It is something like .ic Vx=12V Vy=6V, check in the help file, initial conditions.

Edit:

.IC -- Set Initial Conditions
The .ic directive allows initial conditions for transient analysis to be specified. Node voltages and inductor currents may be specified. A DC solution is performed using the initial conditions as constraints. Note that although inductors are normally treated as short circuits in the DC solution in other SPICE programs, if an initial current is specified, they are treated as infinite-impedance current sources in LTspice.

Syntax: .ic [V(<n1>)=<voltage>] [I(<inductor>)=<current>]

Example: .ic V(in)=2 V(out)=5 V(vc)=1.8 I(L1)=300m


Use Initial Conditions. Normally, a DC operating point analysis is performed before starting the transient analysis. This directive suppresses this initialization. The initial conditions of some circuit elements can be can be specified on an instance-per-instance basis. Uic is not a particularly recommended feature of SPICE. Skipping the DC operating point analysis leads to a nonphysical initial condition. For example, consider a voltage source connected in parallel to a capacitance. The node voltage is taken as zero if not specified. Then, in the first time step, an infinite current is required to charge the capacitor. The simulator cannot find a short enough time step to make the current nonsingular, and a "time step too small convergence fail" message is issued.


With questions like this, the help file is really useful.

Jan

Last edited by jan.didden; 19th August 2021 at 10:26 PM.
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Old 19th August 2021, 11:36 PM   #3053
steveu is offline steveu  United States
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1. I place the following batch file in %userprofile%\AppData\Roaming\MicroSoft\Windows\Se ndto
(posting adds a space in Sendto you have to remove)

%~d1
cd %1
del /S *.raw *.log *.fft
pause


I call it Spice cleaner.bat. You just right click the folder you used and sendto it to this batch file. You can wait and do a whole tree later.

2. I noticed yesterday that I could copy and past between schematics. Is this new?

Last edited by steveu; 19th August 2021 at 11:49 PM.
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Old 20th August 2021, 08:26 AM   #3054
Mooly is offline Mooly  United Kingdom
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Installing and using LTspice IV (now including LTXVII). From beginner to advanced.
Quote:
Originally Posted by steveu View Post

2. I noticed yesterday that I could copy and past between schematics. Is this new?
I think you could do that all the way back to LTIV

Post #3007

Installing and using LTspice IV (now including LTXVII). From beginner to advanced.
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Old 25th August 2021, 09:25 PM   #3055
djoffe is offline djoffe  United States
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Jan,

You are asking for an output current smaller than the listed minimum output current of 400 uA. Ask for more output current, and you should see the circuit work well.

Please refer to graph on top left corner of page 6 of the data sheet.
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Old 25th August 2021, 09:26 PM   #3056
jan.didden is offline jan.didden  Europe
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Yes, that is it! Mark T made a similar comment elsewhere. Thanks for that pointer!

Jan
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Old 1st September 2021, 11:21 AM   #3057
Dibya is offline Dibya
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how to measure slew rate?
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Old 1st September 2021, 11:59 AM   #3058
mikelm is offline mikelm  England
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Hi

Am looking for a SPST NC relay in LT SPICE ( latest release )

Any ideas about where to find one ?

Many thanks
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Old 1st September 2021, 09:55 PM   #3059
steveu is offline steveu  United States
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Default square waves

Quote:
Originally Posted by Dibya View Post
how to measure slew rate?
Does anyone have a better answer than driving with a square wave and measuring the plot?

In any case, you may have run up against the initial conditions problem with pulse sources. Using two pulses in series makes a bipolar square wave with zero Volts at time zero. A finite rise time is required but should not be a problem.
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Old 1st September 2021, 10:05 PM   #3060
steveu is offline steveu  United States
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Quote:
Originally Posted by mikelm View Post
Hi

Am looking for a SPST NC relay in LT SPICE ( latest release )

Any ideas about where to find one ?

Many thanks
I found this:
LTspice: Voltage Controlled Switches | Analog Devices

but you may need to add features of real relays like coil inductance and resistance, contact bounce, etc. Be sure you understand the dangers of driving an inductance and the need for a fly-back diode.
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