LTSPICE: startup

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Chris Carlen - 17 May 2005 21:59 GMT

Greetings:

Wouldn't it be nice if SPICE allowed one to set the output
voltage/current of independent sources for computing the operating point
individually per source?

I realize LTSPICE has the "startup" option which can be a help, but
sometimes I want only one source turned off while the others, like power
supplies are left on. I find myself building klunky constructs such as
a pulse source called "delay" which actuates switches to release desired
sources after a specified time.

Also, the startup option in LTSPICE is limited to operating after 5us.
Why the fixed time?

Is it possible to have a new option for indep. sources called "Vdelay"
which sets the output voltage (speaking specifically here about V
sources, of course) during the "Tdelay" period instead of having that
output be set by "Vinitial"?

That would solve this problem in the most fine grained manner perhaps?

Thanks for comments.

Good day!

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Christopher R. Carlen
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Joerg - 17 May 2005 22:33 GMT

Hello Chris,

> Also, the startup option in LTSPICE is limited to operating after 5us.
> Why the fixed time?

So that Jim can't use LTSpice for his fast IC stuff ....?

Regards, Joerg

http://www.analogconsultants.com

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Jim Thompson - 17 May 2005 22:46 GMT

>Hello Chris,
>
[quoted text clipped - 6 lines]
>
>http://www.analogconsultants.com

Sno-o-o-ort ;-)

In PSpice...

STP(x) 1 if x>0.0, 0 if x<0.0

The unit step function can be used to suppress a value until a given
amount of time has passed.

For instance,

{v(1)*STP(TIME-10ns)}

gives a value of 0.0 until 10ns has elapsed, then gives v(1).

...Jim Thompson

I love to cook with wine. Sometimes I even put it in the food.

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Helmut Sennewald - 17 May 2005 23:05 GMT

----- Original Message -----
From: "Jim Thompson" <thegreatone@example.com>
Newsgroups: sci.electronics.cad
Sent: Tuesday, May 17, 2005 11:46 PM
Subject: Re: LTSPICE: startup

>>Hello Chris,
>>
[quoted text clipped - 23 lines]
>
> ...Jim Thompson

Hello Jim,

LTspice has a function u(x) which has the same definition as your STP(x).
It can be used with B(ehavioral)-sources as well as with E-sources.
Your example would then look like

V=V(1)*u(TIME-10ns)

or

with Epoly:

VALUE={V(1)*u(TIME-10ns)}

But as usual I am not surprised that LTspice also understands

V=V(1)*STP(TIME-10ns)

or with Epoly:

VALUE={V(1)*STP(TIME-10ns)}

Best regards,
Helmut

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Jim Thompson - 17 May 2005 23:38 GMT

>----- Original Message -----
>From: "Jim Thompson" <thegreatone@example.com>
[quoted text clipped - 54 lines]
>Best regards,
>Helmut

I'm not surprised either.

...Jim Thompson

I love to cook with wine. Sometimes I even put it in the food.

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Chris Carlen - 18 May 2005 18:36 GMT

> Hello Jim,
>
[quoted text clipped - 20 lines]
> Best regards,
> Helmut

That should suffice to meet my wishes. Thanks.

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_______________________________________________________________________
Christopher R. Carlen
Principal Laser/Optical Technologist
Sandia National Laboratories CA USA
crcarleRemoveThis@BOGUSsandia.gov
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Robert Baer - 18 May 2005 07:18 GMT

>>Hello Chris,
>>
[quoted text clipped - 23 lines]
>
> ...Jim Thompson

Undefined for x=0?

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Jim Thompson - 18 May 2005 15:23 GMT

>>>Hello Chris,
>>>
[quoted text clipped - 24 lines]
>> ...Jim Thompson
> Undefined for x=0?

Pasted directly from the Reference Guide, but should be x >= 0

...Jim Thompson

I love to cook with wine. Sometimes I even put it in the food.

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Electronics Forum / CAD / May 2005

LTSPICE: startup