Electronics > Beginners

LTSpice

(1/3) > >>

TheDood:
I've been having issues with LTspice. How bad does it glitch for others? Can anyone post a link to a download from a trusted source?

Ive been trying to learn by doing simulations but I can't seem to find consistency. I've definitely made errors but today I've tried to make the exact same cct and getting different results. I started out breaking the sims down into smaller parts as suggested. I created a PWM generator cct out of OP Amps (OP07) and can simulate varying frequencies and duty cycles as expected when using a DC voltage source component, but as soon as I replicate the DC voltage source with a DC cct creating ~same voltages, I'm unable to replicate PWM like when using the LTspice Voltage source component??

^^
For an example of this compare files "PWM(1)" & "Regulator1." The top portion of schematic "Regulator1" OP Amp power-rail, PWM inverting input, PWM non inverting input ~matches the "PWM(1)" schematics OP Amp power-rail, PWM inverting input, PWM non-inverting input voltages. 1 gives me a PWM (DC voltage component)  but the other only goes completely high or completely low (DC cct).

I think these next 2 comparisons might be the exact same cct but giving different results. Refer to files "Regulator1" & "PWM2." "Regulator1" bottom portion is disconnected from the live cct and I've made the exact same cct in the top portion of "Regulator1" as the entire "PWM2" file. I've used different bridge diodes but aside from that all components are exactly the same and same layout. Refer to attached waveforms to notice the drastic change in voltages from 1 schematic to the other. I've been staring at it for awhile, so I'm not ruling out simple errors, but I've tried to find them and coming up short.

EDIT:
Both C2's in "Regulator1" & "PWM2" are charging to 170V.. Somewhere between C2 and OP Amp PWM generator string I'm getting different readings?

TheDood:
 :palm:
I found I was missing the 4-way node on the 2nd OP Amp output on the "Regulator1" schematic. Once added it gives the same result as the "PWM2" file.

Now I'm just trying to determine why I've been unable to generate a PWM when using a DC cct to create the V's compared to using the DC V source component?

Zero999:
There's nothing wrong with LTSpice. It's the circuits.

I can tell that circuit won't work because it's powered by a potential divider consisting of 10k and 60k, which will have an output impedance of 10k||60k = 8k57. Scrap the potential divider and run off plain DC. If you want to simulate the bridge rectifier and ripple, it can be done later and just use an AC voltage source with the peak voltage of the transformer's secondary, you plan to use. Potential dividers aren't normally used to power circuit run off the mains, as they provide no isolation. The only time one might be used is for measuring mains voltage, in an application which doesn't require isolation.

The OP07 can't drive such low resistance values as 50R and 15R. Choose resistors which will not result in loading the output excessively.

The LED circuit can't possibly work, because the rectifier doesn't have an AC input voltage.

Oh, please don't post such large, scaled-up images. Size the appropriate window to something reasonable, then go to tool>copy bitmap to clipboard, paste into an image editor and save as a .png.

TheDood:
Well, I've gotten the DC cct to simulate correctly now too. Its simulating like the DC voltage source. Idk, I probably have just been making silly errors.

TheDood:

--- Quote from: Zero999 on December 18, 2019, 07:20:45 pm ---There's nothing wrong with LTSpice. It's the circuits.

I can tell that circuit won't work because it's powered by a potential divider consisting of 10k and 60k, which will have an output impedance of 10k||60k = 8k57. Scrap the potential divider and run off plain DC. If you want to simulate the bridge rectifier and ripple, it can be done later and just use an AC voltage source with the peak voltage of the transformer's secondary, you plan to use. Potential dividers aren't normally used to power circuit run off the mains, as they provide no isolation. The only time one might be used is for measuring mains voltage, in an application which doesn't require isolation.

The OP07 can't drive such low resistance values as 50R and 15R. Choose resistors which will not result in loading the output excessively.

The LED circuit can't possibly work, because the rectifier doesn't have an AC input voltage.

Oh, please don't post such large, scaled-up images. Size the appropriate window to something reasonable, then go to tool>copy bitmap to clipboard, paste into an image editor and save as a .png.

--- End quote ---
Thanks, I was just messing with different values for different components trying to get the correct figures. I've since changed it and its doing what I was expecting. I used an 18V zener and put a cap in parallel with the last 2 R's in the voltage divider and changed R values.

I think I've been making changes and then running the sim but the nodes have changed as well and I've not been reprobing the same points to view where I should be viewing. Thanks for the input, I'll play around with different R values in the OP Amp string.

Navigation

[0] Message Index

[#] Next page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod