LTspice@groups.io

Re: 74HC74 and 74HCT74 trouble

Ganesan

When I unzip. it says couldn't find symbol 74hc74...
cheers
AG

Show quoted text

On 9/25/2011 6:28 PM, h_manbeing wrote:



--- In LTspice@... <mailto:LTspice%40yahoogroups.com>, 
"eric" <ericgoodchild@...> wrote:

Hello I'm using the 74HC lib and trying to get the 74HC72 D flip flop working but it doesn't seem to be working, I tried it with 
several different circuit that were working with the CD4000 lib D flip 
flop with no luck.

I have other parts from the same lib working fine in the same circuit so I'm confident that it's not something I set up wrong.

Could some one confirm that the 74HC74 model doesn't have a bug?

Thanks,
Eric
I uploaded "74HC74.zip" in Temp.

Re: 74HC74 and 74HCT74 trouble

#47385

--- In LTspice@..., "eric" <ericgoodchild@...> wrote:

Hello I'm using the 74HC lib and trying to get the 74HC72 D flip flop working but it doesn't seem to be working, I tried it with several different circuit that were working with the CD4000 lib D flip flop with no luck.

I have other parts from the same lib working fine in the same circuit so I'm confident that it's not something I set up wrong.

Could some one confirm that the 74HC74 model doesn't have a bug?

Thanks,
Eric
I uploaded "74HC74.zip" in Temp.

Re: 74HC74 and 74HCT74 trouble

Ganesan

#47384

Load a simple circuit.. (net list or schematic)?
cheers
AG
Also look at

Show quoted text

On 9/25/2011 5:57 PM, eric wrote:

Hello I'm using the 74HC lib and trying to get the 74HC72 D flip flop 
working but it doesn't seem to be working, I tried it with several 
different circuit that were working with the CD4000 lib D flip flop 
with no luck.

I have other parts from the same lib working fine in the same circuit 
so I'm confident that it's not something I set up wrong.

Could some one confirm that the 74HC74 model doesn't have a bug?

Thanks,
Eric

74HC74 and 74HCT74 trouble

#47383

Hello I'm using the 74HC lib and trying to get the 74HC72 D flip flop working but it doesn't seem to be working, I tried it with several different circuit that were working with the CD4000 lib D flip flop with no luck.

I have other parts from the same lib working fine in the same circuit so I'm confident that it's not something I set up wrong.

Could some one confirm that the 74HC74 model doesn't have a bug?

Thanks,
Eric

Re: Generation of a discrete number of pulses using a triggering signal

#47382

--- In LTspice@..., Ganesan <dg1@...> wrote:

As Rick mentioned, I added
"B1 proxy 0 V=v(t_burst) tripdv=.1v tripdt=1u "
The  output looks ok without any time step control.
Another good work around...
Cheers
AGAG,

I'm not sure I would call it a work around, but perhaps it is.  In any case it works great.  Unfortunately, lots of folks arent't aware of all of capabilities/features of LTspice.

BTW, your solution is a good example of where using a maximum step size is not necessary and it will slow down the simulation when it is not needed.

Rick

Re: Generation of a discrete number of pulses using a triggering signal

Ganesan

#47381

I agree.. I generally don't like to screw around with the step size, 
unless, I have to..
Cheers
AG

Show quoted text

On 9/25/2011 5:32 PM, Rick wrote:



--- In LTspice@... <mailto:LTspice%40yahoogroups.com>, 
Ganesan <dg1@...> wrote:

Rick,
in this case
".options plotwinsize=0"
didn't help..
So i think it is a time step control issue..
cheers
AGAG,

Yes, in this case that is correct, because, as I said, there are no 
other dynamics to limit the step size. The step time control algorithm 
doesn't know what to do except to limit the maximum step size to 1/50 
or 1/100 (I forgot which, but it doesn't matter) of the total 
simulation time.

However, the only reason I took this time to send my last message was 
to try to explain to you that this particular case is somewhat of an 
exception, and that indiscriminate use of a maximum step size is not 
usually the best solution.

Rick_

Re: Generation of a discrete number of pulses using a triggering signal

#47380

--- In LTspice@..., Ganesan <dg1@...> wrote:

Rick,
in this case
".options plotwinsize=0"
didn't help..
So i think it is a time step control issue..
cheers
AGAG,

Yes, in this case that is correct, because, as I said, there are no other dynamics to limit the step size.  The step time control algorithm doesn't know what to do except to limit the maximum step size to 1/50 or 1/100 (I forgot which, but it doesn't matter) of the total simulation time.

However, the only reason I took this time to send my last message was to try to explain to you that this particular case is somewhat of an exception, and that indiscriminate use of a maximum step size is not usually the best solution.

Rick

Commenting out

Apparajan

#47379

Instead of removing a Bsource, I tried to comment it out by naming it as *B1.. LTspice still extracted it with a weird syntax... Anyone know what is going on?
Cheers
AG

Re: Generation of a discrete number of pulses using a triggering signal

Ganesan

#47378

Rick,
in this case
".options plotwinsize=0"
didn't help..
So i think it is a time step control issue..
cheers
AG

Show quoted text

On 9/25/2011 5:11 PM, Rick wrote:



--- In LTspice@... <mailto:LTspice%40yahoogroups.com>, 
Ganesan <dg1@...> wrote:

Moral of the story : When in doubt put a small step size..
Cheers
AGAG,

In general, this will work. However, this may slow down the simulation 
unnecessairly; especially if it is a large circuit with lots of 
dynamics. If there are other dynamics in the system that cause the 
step size to be reduced, specifying a maximum step size may not be 
necessary. It is best to let the step time control algorithm of 
LTspice control the step size, where possible. (In this specific case 
there are no other dynamics.) Also LTspice uses data compression for 
the .raw file; this means it does not store every data point. To turn 
off the compression use .options plotwinsize=0. Finally, if you have 
BV or BI sources with fast transitions, use tripdv and tripdt to be 
sure to capture them. (See the Help file, for more information.)

Rick

Re: Generation of a discrete number of pulses using a triggering signal

Ganesan

#47377

As Rick mentioned, I added
"B1 proxy 0 V=v(t_burst) tripdv=.1v tripdt=1u "
The  output looks ok without any time step control.
Another good work around...
Cheers
AG

Show quoted text

On 9/25/2011 4:28 PM, Rick wrote:



--- In LTspice@... <mailto:LTspice%40yahoogroups.com>, 
Ganesan <dg1@...> wrote:


Helmut,
I had to make the time step less than 10u in the transient analysis to
keep the triggered pulses from looking weird.. Another interpolation
artifact?
Cheers
AGAG,

Since no maximum step size is specified, LTspice will allow it to 
increase to something like 1/50 or 1/100 of the total simulation time. 
This is why you see the distortion. The solution, in this case, is to 
specify a maximum step size. In cases where there are BV or BI 
sources, the use of tripdv and tripdt can be used to capture fast 
transitions.

Rick

.

Re: Generation of a discrete number of pulses using a triggering signal

#47376

--- In LTspice@..., Ganesan <dg1@...> wrote:

Moral of the story : When in doubt put  a small step size..
Cheers
AGAG,

In general, this will work. However, this may slow down the simulation unnecessairly; especially if it is a large circuit with lots of dynamics.  If there are other dynamics in the system that cause the step size to be reduced, specifying a maximum step size may not be necessary.  It is best to let the step time control algorithm of LTspice control the step size, where possible.  (In this specific case there are no other dynamics.)  Also LTspice uses data compression for the .raw file; this means it does not store every data point.  To turn off the compression use .options plotwinsize=0.  Finally, if you have BV or BI sources with fast transitions, use tripdv and tripdt to be sure to capture them.  (See the Help file, for more information.)

Rick

Re: Generation of a discrete number of pulses using a triggering signal

Ganesan

#47375

Moral of the story : When in doubt put  a small step size..
Cheers
AG

Show quoted text

On 9/25/2011 4:48 PM, Helmut wrote:



--- In LTspice@... <mailto:LTspice%40yahoogroups.com>, 
"Rick" <sawreyrw@...> wrote:



--- In LTspice@... <mailto:LTspice%40yahoogroups.com>, "Helmut" <helmutsennewald@> wrote:
Hello,

The TRIGGER command only works with V-sources.
I have made an example for you using the a pulse source
with the parameter NCYCLES set to the number of pulses.

Files > Tut > TRIGGER > trigger_pulse_burst.asc



Best regards,
Helmut
Helmut,

If I add a maximum step size of 1m and plot the trigger
source and the pulse busrt repeatedly, sometimes the
plot display flickers and the simulation time is about
4 time longer than other times. Do you know what is
going on.

Rick
Hello Rick,

When I use a time step of 1ms, it's damn fast.
Total elapsed time: 0.281 seconds

With 10u max. time step I got the following simulation time.
Total elapsed time: 6.766 seconds.

My Laptop has a dual core CPU with 1.5GHz.

Best regards,
Helmut <>

.

Re: Generation of a discrete number of pulses using a triggering signal

#47374

--- In LTspice@..., "Rick" <sawreyrw@...> wrote:



--- In LTspice@..., "Helmut" <helmutsennewald@> wrote:
Hello,

The TRIGGER command only works with V-sources.
I have made an example for you using the a pulse source
with the parameter NCYCLES set to the number of pulses.

Files > Tut > TRIGGER >	trigger_pulse_burst.asc



Best regards,
Helmut
Helmut,

If I add a maximum step size of 1m and plot the trigger
source and the pulse busrt repeatedly, sometimes the
plot display flickers and the simulation time is about
4 time longer than other times.  Do you know what is
going on.

Rick
Hello Rick,

When I use a time step of 1ms, it's damn fast.
Total elapsed time: 0.281 seconds

With 10u max. time step I got the following simulation time.
Total elapsed time: 6.766 seconds.

My Laptop has a dual core CPU with 1.5GHz.

Best regards,
Helmut

Re: Generation of a discrete number of pulses using a triggering signal

#47373

--- In LTspice@..., "Helmut" <helmutsennewald@...> wrote:
Hello,

The TRIGGER command only works with V-sources.
I have made an example for you using the a pulse source
with the parameter NCYCLES set to the number of pulses.

Files > Tut > TRIGGER >	trigger_pulse_burst.asc



Best regards,
Helmut
Helmut,

If I add a maximum step size of 1m and plot the trigger source and the pulse busrt repeatedly, sometimes the plot display flickers and the simulation time is about 4 time longer than other times.  Do you know what is going on.

Rick

Re: Generation of a discrete number of pulses using a triggering signal

#47372

--- In LTspice@..., Ganesan <dg1@...> wrote:


Helmut,
I had to make the time step less than 10u in the transient analysis to
keep the triggered pulses from looking weird.. Another interpolation
artifact?
Cheers
AGAG,

Since no maximum step size is specified, LTspice will allow it to increase to something like 1/50 or 1/100 of the total simulation time.  This is why you see the distortion.  The solution, in this case, is to specify a maximum step size.  In cases where there are BV or BI sources, the use of tripdv and tripdt can be used to capture fast transitions.

Rick

Re: Generation of a discrete number of pulses using a triggering signal

#47371

--- In LTspice@..., Ganesan <dg1@...> wrote:


Helmut,
I had to make the time step less than 10u in the transient
analysis to keep the triggered pulses from looking weird.
Another interpolation artifact?
Cheers
AGHello AG,

Thanks for the hint with the maximum time step.
I have uploaded an updated version.

Files > Tut > TRIGGER > trigger_pulse_burst.asc

Best regards,
Helmut

Re: Generation of a discrete number of pulses using a triggering signal

Ganesan

#47370

Helmut,
I had to make the time step less than 10u in the transient analysis to 
keep the triggered pulses from looking weird.. Another interpolation 
artifact?
Cheers
AG

Show quoted text

On 9/25/2011 4:01 PM, Helmut wrote:



--- In LTspice@... <mailto:LTspice%40yahoogroups.com>, 
"kostas045" <kostas045@...> wrote:

Hi all,

I have been trying to generate a discrete number of pulses based on a triggering signal, to drive a mosfet. The trick is that a want the 
sequence of pulses to be repetitive during the simulation, i.e. I dont 
want to generate it only once!

For example given a triggering event, like a sinus reaching its peak value or zero or whatever, a first sequence of X high frequency pulses 
will be generated. The second sequence will be generated at the next 
triggering event and so on...

I have been trying with a BV source and the keyword ''Trigger'' (as I found in some other posts in this forum) but until now all my 
efforts have been proven unworthy! Any help will be appreciated!

Thanks!

P.S. Great forum guys! Gongrats!
Hello,

The TRIGGER command only works with V-sources.
I have made an example for you using the a pulse source
with the parameter NCYCLES set to the number of pulses.

Files > Tut > TRIGGER > trigger_pulse_burst.asc



Best regards,
Helmut

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Re: Generation of a discrete number of pulses using a triggering signal

#47369

--- In LTspice@..., "Helmut" <helmutsennewald@...> wrote:

--- In LTspice@..., "kostas045" <kostas045@> wrote:

Hi all,

I have been trying to generate a discrete number of pulses based on a triggering signal, to drive a mosfet. The trick is that a want the sequence of pulses to be repetitive during the simulation, i.e. I dont want to generate it only once!

For example given a triggering event, like a sinus reaching its peak value or zero or whatever, a first sequence of X high frequency pulses will be generated. The second sequence will be generated at the next triggering event and so on...

I have been trying with a BV source and the keyword ''Trigger'' (as I found in some other posts in this forum) but until now all my efforts have been proven unworthy! Any help will be appreciated!

Thanks!

P.S. Great forum guys! Gongrats!
Hello,

The TRIGGER command only works with V-sources.
I have made an example for you using the a pulse source
with the parameter NCYCLES set to the number of pulses.

Files > Tut > TRIGGER >	trigger_pulse_burst.asc

Best regards,
Helmut

Super! Exactly what I was aiming for! Thank you very much Helmut!

Regards!
Kostas

Re: Generation of a discrete number of pulses using a triggering signal

#47368

--- In LTspice@..., "kostas045" <kostas045@...> wrote:

Hi all,

I have been trying to generate a discrete number of pulses based on a triggering signal, to drive a mosfet. The trick is that a want the sequence of pulses to be repetitive during the simulation, i.e. I dont want to generate it only once!

For example given a triggering event, like a sinus reaching its peak value or zero or whatever, a first sequence of X high frequency pulses will be generated. The second sequence will be generated at the next triggering event and so on...

I have been trying with a BV source and the keyword ''Trigger'' (as I found in some other posts in this forum) but until now all my efforts have been proven unworthy! Any help will be appreciated!

Thanks!

P.S. Great forum guys! Gongrats!
Hello,

The TRIGGER command only works with V-sources.
I have made an example for you using the a pulse source
with the parameter NCYCLES set to the number of pulses.

Files > Tut > TRIGGER >	trigger_pulse_burst.asc

Best regards,
Helmut

Generation of a discrete number of pulses using a triggering signal

#47367

Hi all,

I have been trying to generate a discrete number of pulses based on a triggering signal, to drive a mosfet. The trick is that a want the sequence of pulses to be repetitive during the simulation, i.e. I dont want to generate it only once!

For example given a triggering event, like a sinus reaching its peak value or zero or whatever, a first sequence of X high frequency pulses will be generated. The second sequence will be generated at the next triggering event and so on...

I have been trying with a BV source and the keyword ''Trigger'' (as I found in some other posts in this forum) but until now all my efforts have been proven unworthy! Any help will be appreciated!

Thanks!

P.S. Great forum guys! Gongrats!

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