Data Sheet

Proteus VSM
231
cursor should be at the corner at the start of the falling edge. You should find that the falling
edge is a little under 10m.
Using Current Probes
Now that we have finished with our measurements, we can return to the circuit – just close the
maximised graph for the cross at the right of the tab.
We shall now use a current probe to examine the current flow around the feedback path, by
measuring the current into R4.
Current probes are used in a similar manner to voltage probes, but with one important
difference. A current probe needs to have a direction associated with it. Current probes work by
effectively breaking a wire, and inserting themselves in the gap, so they need to know which
way round to go. This is done simply by the way they are placed. In the default orientation
(leaning to the right) a current probe measures current flow in a horizontal wire from left to right.
To measure current flow in a vertical wire, the probe needs to be rotated through 90° or 270°.
Placing a probe at the wrong angle is an error, that will be reported when the simulation is
executed. If in doubt, look at the arrow in the symbol. This points in the direction of current
flow.
Select a current probe by clicking on the Current Probe icon. Click left on the clockwise Rotation
icon such that the arrow points downwards. Then place the probe on the vertical wire between
the right hand side of R4 and U1 pin 6.
Add the probe to the right hand side of the graph by tagging and dragging onto the right hand
side of the minimised graph. The right side is a good choice for current probes because they are
normally on a scale several orders of magnitude different than the voltage probes, so a
separate axis is needed to display them in detail.