I am trying to add TRIPDT and TRIPDV parameters to a behavioral voltage source in QSPICE, but when the simulation runs, it returns an error:
Warning: Ignoring unknown instance parameter “TRIPDT” of device B1.
To add these, I right-clicked on the source and selected the “Add New Attribute” option. Is there any way to add these parameters, or something with an equivalent effect, to behavioral sources in QSPICE?
Those are LTspice parameters, which helped when implementing logic with B-devices. QSPICE doesn’t expect logic in B-devices, so I didn’t implement them in the QSPICE B-devices.
I am curious about this topic too, @Engelhardt.
I am starting out with Qspice and was attempting to make a Duty-to-PWM generator. The way I would normally do this in ltspice is with a BV source + the tripdt & tripdv parameters like @rankin said. I tried that here, but it looks like Qspice isn’t increasing the sampling frequency at the crossover event (so the PWM waveform has a very slow falling edge). I recreated the same thing with a Schmitt comparator, and a custom c-code block. All of them result in the same thing (different hysteresis values - so they’re slightly different results).
I can get a better result by forcing a max step size… but that kind of defeats the point.
Questions is – if not tripdt and tripdv, how would I go about building a circuit like this one? Maybe Qspice is doing something intelligent that I’m failing to understand?
The Schmitt device accepts ttol, the temporal tolerance. Add an attribute ttol=1n to it. It’s the analog B-devices that don’t get a temporal tolerance anymore.
Thanks @Engelhardt - confirmed that works. Picture attached.
Follow-up question - Is any type of temporal tolerance supported for the c-code blocks? I looked through the documentation but couldn’t find anything. I can think of quite a few instances where it’d be really useful, so I’d be pretty happy to hear if it’s supported.
Yes, the C-code blocks give the utmost in temporal control, but they are written inside the code. Look inside the PracticalSMPS.qsch example.
Thanks for the quick response. I am used to using b-sources for logical functions in LTspice, but it seems like figuring out how to use code blocks to accomplish the same functions would be better in the long term.
I too encountered this problem recently and at the suggestion of a colleague, I set the maximum timestep to a value on the order of the desired rise and fall time and the situation seemingly improved. I like this explanation better than the original one I hypothesized.
BRUCE108
