Author Topic: LTspice  (Read 1850 times)

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Offline Nikos A.Topic starter

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LTspice
« on: October 22, 2019, 04:41:24 pm »
Hi everyone.

I am trying to learn some basics on TLspice and I cannot figure out what I am doing wrong. I am using a P-channel Mosfet, a voltage source and a load. When the voltage source (ig battery) is reversed the Mosfet should be OFF because of Vgs>0 isn't it?
Why I am measuring a negative voltage after the Mosfet and current passing through the load??

Thanks in advance

 

Offline StillTrying

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Re: LTspice
« Reply #1 on: October 22, 2019, 04:53:45 pm »
I1 is probably producing its own voltage, replace I1 with a 60R.
.  That took much longer than I thought it would.
 

Offline Ian.M

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Re: LTspice
« Reply #2 on: October 22, 2019, 04:54:48 pm »
StillTrying beat me to it.

Don't use a current source as a load!!!

As he said, replace I1 with a 60 ohm resistor and it will all make sense.

I would also suggest putting V1 back the right way round then running a DC sweep with .dc V1 -12 12 instead of .tran 1ms, which will show you when the MOSFET's channel has enough gate voltage to take over from its body diode. (Not that simmed gate thresholds are to be trusted - there's far too much variation between batches of the same part.)
 

Offline SiliconWizard

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Re: LTspice
« Reply #3 on: October 22, 2019, 05:06:29 pm »
To use a current source as a proper load in LTSpice, you can just tick the "active load" parameter in the current source parameters' dialog. It will act as you would expect. Very handy.
 
The following users thanked this post: TimNJ, edavid, SilverSolder

Online Zero999

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Re: LTspice
« Reply #4 on: October 22, 2019, 06:50:15 pm »
To use a current source as a proper load in LTSpice, you can just tick the "active load" parameter in the current source parameters' dialog. It will act as you would expect. Very handy.
Yes, right click the component and click advanced to get the active load parameter.
 

Offline Nikos A.Topic starter

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Re: LTspice
« Reply #5 on: October 22, 2019, 07:22:10 pm »
Thank you guys!! I am going to run the simulation tomorrow and return with a feedback  :D

 

Offline Simon

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Re: LTspice
« Reply #6 on: October 22, 2019, 08:45:11 pm »
 

Offline Nikos A.Topic starter

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Re: LTspice
« Reply #7 on: October 22, 2019, 08:49:12 pm »
If you don't mind readng there is "the book": https://simonselectronics.co.uk/product/the-ltspice-iv-simulator-wurth-elektronik/

Thank you Simon, I didn't know about that!!
 

Offline ogden

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Re: LTspice
« Reply #8 on: October 22, 2019, 09:10:48 pm »
If you don't mind readng there is "the book": https://simonselectronics.co.uk/product/the-ltspice-iv-simulator-wurth-elektronik/

Sorry Simon, but there's better deal on Amazon :-//    Some university classes are done using LTspice. By aiming search queries accordingly you can get some course handouts that most likely is not so comprehensive as book, but may still be helpful enough. Just random internet search hit.
 

Offline Jay_Diddy_B

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Re: LTspice
« Reply #9 on: October 23, 2019, 02:06:23 am »
Hi,

Let us explore the effect of checking the load box, that was proposed by Zero999.

Here is a model:




There is a standard current source I1.

A current source with the load box checked. Note that the current is zero for zero volts and goes to the set point at 0.4V This is handy in some applications.

There is also a behavioral current source that is 1A if the voltage is greater than 0.

And the results:




Regards,

Jay_Diddy_B
 

Offline Jay_Diddy_B

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Re: LTspice
« Reply #10 on: October 23, 2019, 02:18:00 am »
Nikos A,

Try this:




Regards,
Jay_Diddy_B
 

Offline StillTrying

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Re: LTspice
« Reply #11 on: October 23, 2019, 11:12:00 am »
If you don't mind readng there is "the book": https://simonselectronics.co.uk/product/the-ltspice-iv-simulator-wurth-elektronik/

I think you've overdone the 000s, 1.6 billion LT users? :o 1.6 million ..perhaps. ^-^
.  That took much longer than I thought it would.
 

Offline Simon

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Re: LTspice
« Reply #12 on: October 26, 2019, 07:57:42 pm »
If you don't mind readng there is "the book": https://simonselectronics.co.uk/product/the-ltspice-iv-simulator-wurth-elektronik/

Sorry Simon, but there's better deal on Amazon :-//    Some university classes are done using LTspice. By aiming search queries accordingly you can get some course handouts that most likely is not so comprehensive as book, but may still be helpful enough. Just random internet search hit.

True, I'm one of them :( just wait until I see that asshole from wurth that sold them to me.
 


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