DC sweep

DC sweep performs a sequence of DC operating point simulations. It increments the voltage or current of a selected source in predefined steps over a range of values. DC sweep can be used with any source that includes a DC offset variable.

An optional second source can also be used to run a nested sweep. 

During simulation: 

• Capacitors are treated as open circuits. 
• Inductors are treated as short circuits. 
• Only DC values of voltage and current sources are used. 

Sweeping a single source 

The following is a simple Zener regulator circuit where the diode maintains a nearly constant breakdown or Zener voltage as the current through it changes. In this case, the Zener voltage is 5 V.

You can build this circuit, or open it from the Help Circuits user group and save your own copy. This is a closed group. You can open and copy the circuits in this group, but you cannot join it.

Set up and run the sweep:

1. Build the above circuit. 
2. Tap , expand Simulation settings and select DC sweep. 
   V1 is automatically selected as the source.
3. Enter a Start value of 0 V, a Stop value of 10 V, and an Increment of 1 V. 
   Notice that Points are set to 11. If you change the Increment value, the number of points will change accordingly.
4. Tap Start simulation. 
   The grapher opens with the following results:
   
   The sweep parameters were set so that datapoints were measured at 1 V intervals, for example, the selected datapoint above (7.0000V, 5.0005V). 
   
   Notice that the output voltage stabilizes at approximately 5 V as expected. 
   
   For a smoother curve, enter a smaller Increment, for example, 0.1 V, which will yield 101 datapoints.
   
   Cursors

   You can switch on cursors to get more information. X axis, Y axis and Track cursors are available for DC sweep simulation. 

   In the following example, X Axis is selected from the Type drop-down menu, in Cursors. 

   The table displays the X and Y axis values for Cursor 1. Similar values are displayed for Cursor 2. 

   The third column of the table displays ΔX = X2 - X1.

   The fourth column displays 1/ΔX. 

   

   Notice how the data in the table changes when you select Y Axis for the cursor Type: 

   

   When Track is selected as the cursor Type, the table contains data similar to the following: 

   

Nested sweeps

Nested sweeps are useful for measuring a transistor's characteristic current-voltage, I-V, curves, as demonstrated below. 

You can build this circuit (I-V curves), or make a copy of it from the Help Circuits user group. 

Set up and run the sweep:

1. Build the above circuit. 
2. Tap , expand Simulation settings and select DC sweep. 
3. Select V1 as Source 1 and set the following:
   Start value  0 V
   Stop value  10 V
   Increment   0.5 
4. Select I1 as Source 2 and set the following:
   Start value  0 A
   Stop value  0.00025 A
   Increment   0.00005 A
5. Tap Start simulation.
   The grapher opens with the following results.The legend includes the component that was swept and its Start and Stop values. 
   
   Each curve represents one value of Source 2 (I1). The 0 A curve was generated by its Start value of I1 = 0 A. 
   
   The next curve was generated when I1 incremented to 5e-05 A. Hover the cursor over a trace to read its datapoints. The data label shows the value of Source 2 in the title.
   
   
   Cursors
   

   You can switch on cursors to get more information. X axis, Y axis and Track cursors are available for nested DC sweep simulations. 

   In the following example, X Axis is selected from the Type drop-down menu, in Cursors. 

   The table displays the X and Y axis values for Cursor 1. Similar values are displayed for Cursor 2. 

   The third column of the table displays ΔX = X2 - X1.

   The fourth column displays 1/ΔX.
   
   You can change which of the nested sweeps a cursor reads by selecting it from the second drop-down. In the example below, Cursor 1 reads the data from PR1 for the sweep when I1 = 0 A. 

   

   Notice how the data in the table changes when you select Y Axis for the cursor Type:  

   

   When Track is selected as the cursor Type, the table contains data similar to the following: