LTspice syntax problem

[Faringdon]

Hi,
How do i make the time of a "Pulse" source equal to the voltage of a node in LTspice?
The attached LTspice wont work. Do you know how to solve?

[SiliconWizard]

As we already explained in an earlier thread, you can't have *parameters* in a simulation that are time-dependent, even less so depending on a node voltage or on a current. Parameters can only be constants for the whole simulation; the simulator can step parameters over some range though - in this case, it will just launch as many simulations as there are steps, every time with a new constant value for said parameters. Not at all what you want here.

Also as we explained earlier, you can use an arbitrary voltage source for this. A sin function combined with some thresholding function could get you a voltage-dependent pulse width generator.

Alternatively, you can look at one of the "modulate" models in the "Special Functions".

[Ian.M]

Yep. It was https://www.eevblog.com/forum/eda/ltspice-if-statement-syntax/ three weeks ago . . .

I wonder if our O.P. also struggles with object permanence?

[Zero999]

Oh well, last time I did this with a comparator. Now lets try a behavioural voltage source.

[Zero999]

Drat. That's already been done before. I should have read the other thread properly.

Oh well, for fun, here's another way.

[Ian.M]

LTC (now AD) have a chip for that.  The LTC6992-1 TimerBlox VCPWM does the core of what our O.P. wants, both in LTspice and real life!

Input and output voltage scaling is left as an exercise for the user . . . 

[Zero999]

The original poster appears to have forgotten about this thread.

I just thought I'd post this, simply because I couldn't think of anywhere else to post it. I wanted to see how well the voltage controlled switch could simulate an open collector comparator.