Re: Simulation runs very slowly: test.asc
|
Hi Tony, thanks. ? ??????????? I extracted your zip file into a folder and ran your .asc from there. Would you still recommend your 1st paragraph to fix the problem? ? ??????????? ¡°The ideal current source causes the LM317A come out of regulation because the output voltage is too low.¡± ??????????????? I don¡¯t understand. I would think that as long as IN ¨C OUT exceeds 5V and OUT = ?ADJ + 1.25V, the LM317 should operate properly. This is the case in my original circuit. That ADJ is at a negative voltage should be irrelevant. This is not a practical circuit, just a proof of concept. ? ??????????????? Yes, figure 26. I1 flows through Rc2 creating a voltage drop between the load and the ADJ terminal. The LM317 maintains the 1.25 V difference between OUT and ADJ, but the voltage drop across Rs2 is lessened. Different values of I1 lead to different drops across Rc2 and different RL2 load currents. ??????????? ?
toggle quoted message
Show quoted text
From: [email protected] <[email protected]> On Behalf Of Tony Casey via groups.io
Sent: Sunday, April 6, 2025 2:00 PM
To: [email protected]
Subject: Re: [LTspice] Simulation runs very slowly: test.asc? Aah. I think LTspice didn't update the symbol reference in the schematic. Delete the LM317A symbols from the schematic and reload the replacement symbol LM317A.asy. It sounds like the old symbol was being used that had the hard-coded ModelFile. I've updated the zip file to make sure that does happen.
The ideal current source causes the LM317A come out of regulation because the output voltage is too low.
If I was making a programmable current source, I probably wouldn't choose the LM317 as the basis, because the voltage feedback doesn't operate the same way as the classic series regulator. I guess you were working from Figure 26 in the LM317A datasheet? I don't really understand what you were trying to accomplish with the additional current source. I don't think it quite does what you were looking for because all that is relevant to the output current is the resistance between OUT and ADJ, as V(out,adj) is maintained at 1.25V by the feedback. ? On 06/04/2025 19:19, Christopher Paul via groups.io wrote: Thank you, Tony, for the corrected Lib file. I got the file I was using from one posted this year in the user¡¯s temp folder. Maybe you¡¯d like to post an update? ? I intended that RL2 have 10mA through it, and 1V across it. I don¡¯t see why a negative voltage on ADJ would be a problem as long as the OUT minus ADJ pin voltage is appropriate, and it is. Please keep in mind that this is not intended to be a practical circuit, only a proof of concept. Kindly comment. ? I am still getting the following error messages when I run your file.: ? u1:_u1_u12:dd1: Emission coefficient, N=4.83179e-313, too small, limited to 0.1 u1:_u1_u11:dd1: Emission coefficient, N=4.83179e-313, too small, limited to 0.1 u2:_u1_u12:dd1: Emission coefficient, N=4.83179e-313, too small, limited to 0.1 u2:_u1_u11:dd1: Emission coefficient, N=4.83179e-313, too small, limited to 0.1 Direct Newton iteration for .op point succeeded. ? I am unfamiliar with the round(I(RL2)*1e4)/1e4 instruction you used and can¡¯t find a reference to it in my Help instructions. Can you direct me to where I could find information about it? I¡¯m still using LTspice 17.1.14.
?
|
