LTSpice woes: oscillation and logic controls

A

ACharnley

Member

• Sep 4, 2018

• #1

As much as I love this software I equally hate it.

Working with FETs and voltages I find myself more and more using GPIO's to make decisions, which requires emulating the hysteresis logic they'd contain otherwise LTspice goes into loops. Unless I'm missing a trick I end up doing multiple B source's which reference one another. The approach works but after a while the multiple IF's become a pain (I sometimes have 4!).

Surely there's a better way?!?

Q) Is it possible to set params dynamically?
Q) Is it possible to condense these IF's using standard operators: && ||

 

rjenkinsgb

Well-Known Member

Most Helpful Member

• Sep 4, 2018

• #2

Does it have emulations of single schmitt triggers such as 74HC14, CD40106 etc?

Depending what you are doing, they may work.

 

alec_t

Well-Known Member

Most Helpful Member

• Sep 4, 2018

• #3

Have you tried using the 'A' devices? You can set their parameters (e.g. you can set the Schmitt buffer threshold and hysteresis, so that it behaves like a comparator), but AFAIK you can't set any parameters dynamically.

 

E

eTech

Well-Known Member

• Sep 4, 2018

• #4

.

 

Last edited: Sep 4, 2018

A

ACharnley

Member

• Sep 19, 2018

• #5

alec_t, bingo - that's exactly what I needed.

Now, how to get the schmitt inverse pin to include a deadzone?

 

crutschow

Well-Known Member

Most Helpful Member

• Sep 19, 2018

• #6

alec_t said:

Have you tried using the 'A' devices?

Click to expand...

What are "A" devices?

 

alec_t

Well-Known Member

Most Helpful Member

• Sep 20, 2018

• #7

They're in the LTS 'Digital' folder and are primitive ideal gates with 1V logic by default.

 

alec_t

Well-Known Member

Most Helpful Member

• Sep 20, 2018

• #8

ACharnley said:

Now, how to get the schmitt inverse pin to include a deadzone?

Click to expand...

Use the Vt and Vh parameters, as explained in 'Help'.

 

A

ACharnley

Member

• Sep 20, 2018

• #9

I mean't a deadzone between the inverting and non inverting pin. VT/Vh is hysteresis?

 

alec_t

Well-Known Member

Most Helpful Member

• Sep 20, 2018

• #10

Don't think that's possible. Try using a pair of gates or switches.

 

E

eTech

Well-Known Member

• Sep 20, 2018

• #11

ACharnley said:

alec_t, bingo - that's exactly what I needed.

Now, how to get the schmitt inverse pin to include a deadzone?

Click to expand...

The A devices don’t support that functionality. You’ll have to use a combination of A devices.

Maybe use a clock source with a leading and trailing edge detectors. The pulse width of the clock source could then set the “dead” time.

eT

 

alec_t

Well-Known Member

Most Helpful Member

• Sep 20, 2018

• #12

Here's one way :


Param 'on' sets the dead zone between b and d.

 

E

eTech

Well-Known Member

• Sep 20, 2018

• #13

Here's another way.


param DT sets Dead Time
param DTmin sets minimum Dead Time
param Freq sets operating frequency

 

A

ACharnley

Member

• Sep 24, 2018

• #14

That's clean alex_t. I used that approach with another schmidt to make an adjustable duty cycle.