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In this OrCAD project, I tried to build a really basic DC-DC converter with use of "S" or "SBreak" parts in OrCAD's Analog Library. But, according to analysis (picture below), the blue DC line should be equal to 5 VDC, but OrCAD says it's at 0 V.

I know that the part "S" or "SBreak" is working with "VON" and "VOFF" voltage levels and on their working/closing resistances "RON" and "ROFF". What and how is it with "S" switches and how to use them effectively?

MY Screen

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  • \$\begingroup\$ Blue line or green line? Check in the OrCAD data for the VCswitch what the open circuit impedance is - it might be set to zero ohms and it needs to be set to a big number. Alternatively the closed circuit resistance may be set stupidly high - I can't see the blue line so I don't really know what is meant to be happening. OK I opened the picture and I can see a faint blue line!!!! \$\endgroup\$
    – Andy aka
    Mar 7, 2014 at 17:57
  • \$\begingroup\$ @Andyaka The green line is Voltage Input for the circuit. I mean the blue line which is the Voltage Output for the circiut. The Blue line can be seen on right picture 0V-bottom-side. The question is why the blue line is on the 0V. + Yes stupidly but because I want to show only voltage not current so I changed it very high. Vice versa, the same situation occured. \$\endgroup\$
    – Bay
    Mar 7, 2014 at 18:01
  • \$\begingroup\$ What is the on and off resistances of the VC switch set to? \$\endgroup\$
    – Andy aka
    Mar 7, 2014 at 18:02
  • \$\begingroup\$ I really don't know. But, in my view, if switch open, ROFF is online. If switch close, RON is online. This situation may be about switch loses. \$\endgroup\$
    – Bay
    Mar 7, 2014 at 18:04
  • \$\begingroup\$ OrCAD will tell you those values somewhere - this is likely what is wrong \$\endgroup\$
    – Andy aka
    Mar 7, 2014 at 18:05

1 Answer 1

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Look what you have in your picture: -

enter image description here

How can you expect sensible results with Ron at a 2,000,000 ohms and Roff at 1,000,000 ohms. With these value the voltage across the ten ohm resistor is going to be about 50 microvolts when the switch is off and about 25 microvolts when the switch is on. Is this what you see?

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  • \$\begingroup\$ Very special thanks for you! Everything is now clear! :) \$\endgroup\$
    – Bay
    Mar 7, 2014 at 18:47

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