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I am simulating a dc analog circuit comprising transistor, opamp and resistors. In Ltspice, if I run a Op point analysis for a boundary value of my input voltage I get unexpected reults. (This is shown in image as current through Resistor R6 which is I(R6) )

Op Point Analysis

However, if I run a DC Sweep Anaylsis for whole range of input voltage including boundary values, I get the results as expected. This is shown in image below that I get different value of Resistor R6 current for same value of input voltage Vin = 6.1

DC Sweep

As both of these Analysis are DC and calculate node voltages and current, this discrepancy between both analysis is to my surprise.

Can anyone share his experience ? which result is the right one ??

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  • \$\begingroup\$ Many sources have different settings for operating point and DC sweep analysis. Do the operating point analysis and check that all DC voltages are how you want them. Also you should include the schematic you're using. \$\endgroup\$
    – Bimpelrekkie
    Commented May 5, 2017 at 10:08
  • \$\begingroup\$ Is it possible to edit/ access these settings or how to edit them in a way that they yield same results for both type of analysis. The schematic that I am analyzing is here - electronics.stackexchange.com/questions/302124/… \$\endgroup\$
    – HerrderElektronik
    Commented May 5, 2017 at 11:18
  • \$\begingroup\$ Show the spice commands that your using to run each analysis and the conditions for your sources. \$\endgroup\$
    – Voltage Spike ♦
    Commented May 5, 2017 at 16:24
  • \$\begingroup\$ @laptop2d for operating point analysis, i just set the input voltage, write a command .op and let the simulation run.. in other case i sweep input voltage Vin accross a range of voltages writing- .dc Vin 0.5 6.5 0.1 .. The input voltage Vin is shown in the link above i shared \$\endgroup\$
    – HerrderElektronik
    Commented May 8, 2017 at 6:44
  • \$\begingroup\$ My guess is that you aren't setting the sources in the same way in both simulations. But I can't debug this for you, I don't know what your simulation looks like \$\endgroup\$
    – Voltage Spike ♦
    Commented May 10, 2017 at 5:42

1 Answer 1

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I know it's late. I had the exact problem but I solved it. First thing you have to do is making sweep interval much smaller. This way you can get better results. Also, instead of checking points with 0.1 difference you should make it lesser like 0.001. When you do it as you did, DC sweep rolls up the value a bit and this a problem for delicate circuits. Smaller intervals+more point may be your answer.

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