new PSU, should be modified to use a current sink in place of the Zener
reference.

Changes to be committed:
      modified:   .gitignore
      deleted:    sim/psu/interface.asc
      deleted:    sim/psu/interface.log
      deleted:    sim/psu/interface.op.raw
      deleted:    sim/psu/interface.raw
      new file:   sim/psu/smallcurrent.asc
      new file:   sim/psu/smallcurrent.net