See the screen shot of a simulation with LTspice that I did. There is a large discrepancy between the voltage drop across R2 that I expect and what LTspice reports.

With R3 not connected to the circuit and given that the resistance of R1 is 20 times that of R2, I would expect that the voltage drop across R2 equals 500mV. The reading that LTspice gives is 476 mV which is about 5% low.

With R3 connected to the circuit, I would expect that the voltage drop across R2 equals 350 mV. According to LTspice, that voltage equals 444 mV or 27% higher than what would theoretically occur.

Given that the voltage source and R1 are a current source, the voltage across R2 or R3 in parallel with R2 should be directly proportional to the total resistance.
Am I missing something here? I thought that possibly my copy of LTspice was faulty, but reinstalling it didn't change anything.

 

Please post the screenshot (file size limitations apply here) and your .asc file.

 

Hello,

@Alec_t , the filesize over here is quite large.
The maximum filezise is about 10 Mb.
Also you can add 10 attachments to one post.
There are forums with much smaller sizes.

Bertus

 

See the screen shot of a simulation with LTspice that I did. There is a large discrepancy between the voltage drop across R2 that I expect and what LTspice reports.

With R3 not connected to the circuit and given that the resistance of R1 is 20 times that of R2, I would expect that the voltage drop across R2 equals 500mV. The reading that LTspice gives is 476 mV which is about 5% low.

With R3 connected to the circuit, I would expect that the voltage drop across R2 equals 350 mV. According to LTspice, that voltage equals 444 mV or 27% higher than what would theoretically occur.

Given that the voltage source and R1 are a current source, the voltage across R2 or R3 in parallel with R2 should be directly proportional to the total resistance.
Am I missing something here? I thought that possibly my copy of LTspice was faulty, but reinstalling it didn't change anything.

You REALLY need to post the schematic of each circuit variant that you are talking about. Otherwise, there is no way for anyone to make heads or tails of what you are describing. Also, present your calculations, not just your expected numbers. Let people see HOW you arrived at your results so that we are in a position to figure out where you are going wrong (or to verify that you aren't).

 

My apologies, I didn't catch the mistake that I was making until just before I was ready to start the thread. When i recognized my mistake, I wanted to delete the entire post but found that to be impossible. I was attempting to delete everything, bur somehow the text got through.