hi BT,
This what I get with your asc file.???
Do you get a different plot.???
It's not a quirk of the op amp's spice model. The circuit can actually lock up with the op amp output at the positive rail. In your schematic, the transistor saturates, and your feedback becomes positive instead of negative. You can put a diode in series with the collector to prevent the positive feedback, but if the op amp output ever goes high enough to saturate the transistor, i.e., forward bias the c-b junction, the +input pin will be higher than the -input pin, so the "fault" will be stable.Hi Eric,
thanks for checking! The two voltage sources I used, V4 and V3, is just me trying to be clever. I figured the if I connect one Vswitches '+' to a permenant voltage, then to enable it, one would have to pull the '-' input low (assuming a Vt of <1V). So, by changing the voltage of V4, to 1V, S1 is on, and S2 is off, and with V4 = 0V, S1 is off, and S2 is on. I have done this on many simulations (with more than 12 switches..) just saves me changing the value of two voltage sources to switch a group off, and another on.
Thanks for confirming things, I wasn't asking you to spend any time on it, as its not exactly a 'major problem', just one thats niggling at me (never could let things go...).
I was also recently stumped by a simulation of a low current CC/CV supply I paln on building. It used the LM317 model found on this very forum. After 2 hours (I know, you can tell I'm not married eh..) I eventually realised the model had an internal current limit of 845mA - which is the Ilimit for the SOT223 version, not the TO-220... and its little things like that which lead me to believe I'm at fault here.
Well, half way through writing this reply, I got it to work. The PWL settings for the load, start at 10mA. The original: PWL(10m 10m 20m 300m 30m 900m).
I changed the load to '0' at 10ms, so it starts with no load. This works, wit the switch enabled, it behaves as if its shorted, and when disabled, like open (well, a 1Meg resistance, which I can change). Same effect can be achieved by checking 'start external voltages at 0', although I don't always use this as it can take ages for the transient analysis to do its thang (when I'm just checking DC things, and transient response isn't needed).
So after all that, its not a bug, not the Vswitch, and, not *quite* my stupidity. But rather an oddity of the opamps spice model when the simulation starts at full voltage. Sorry if I've wasted your time, just hope it perhaps *maybe* might save some headscratching for you, or others, in future projects.
I hear you, Eric. Thinking back, I built an astonishing number of breadboards before spice became available.hi BT,
I started using LTS about 2 years ago, after getting some support/encouragement from 'Roff' and also looking at his Sims.
I try just for the heck of it, to Sim posted circuits in order to practice technique and methods, I wish I had been able to have a modern version of LTS 25yrs ago it would have saved a lot of time and effort in designing.
I hear you, Eric. Thinking back, I built an astonishing number of breadboards before spice became available.
I used several commercial versions of spice during my career (before I retired), both before and after the introduction of LTspice. I never actually used LTspice at work.
My all-time great breadboard was a 9 bit video A/D converter with a conversion rate of 14.3 megasamples/sec. This was in the mid-70's, before integrated A/D's or spice were available. The PC board version went into a very profitable digital video timebase corrector. A picture of the PC board is attached. Its dimensions are 13" x 8.25".Yikes, even though all the modern simulation software must speed up design/time considerably, I bet you enjoyed breadboarding to a certain extentI'm kind of young, but still not up on the latest and greatest software tools - partly because I simply cannot afford expensive software (when the free versions are more than adequate for my needs) and also because I have a real attachment to hardware prototyping. It takes much longer, which means I end up getting paids less for how long it takes me ... but I dunno, spice/software is great, I stil feel more at home with a soldering iron or poking around with a multimeter.
Might sound like brown-nosing, but it really is good to know there are very experienced and knowledgable spice users in the forum (Roff and Eric, and I'm sure there's others).
Nice! looks neater/more modern than many of my boards.... As for stitching together multiple breaboards, now THAT is prototyping at its finest. A hell of a lot of effort, but well worth it
hi BT,
Runs OK for me.
For the OPA look at the LT1006 prec OPA. [its in the LTS library]
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