DC Sweep

DC Sweep Analysis #

DC sweep analysis is a powerful simulation tool in Breadpad that allows you to observe how your circuit responds as you vary a DC voltage or component value. This helps you understand component characteristics, transfer functions, and operating thresholds without physically adjusting your circuit.

What is DC Sweep Analysis? #

DC sweep analysis works by:

  1. Varying a DC voltage source or component parameter over a specified range
  2. Calculating the operating point at each step
  3. Plotting the relationship between the swept parameter and circuit outputs

Unlike transient analysis, which shows behavior over time, DC sweep shows the relationship between input and output voltages or currents.

When to Use DC Sweep Analysis #

DC sweep is particularly useful for:

  • Determining transistor characteristics (gain, threshold voltages)
  • Finding the threshold voltage of logic gates
  • Analyzing the transfer function of amplifiers
  • Testing voltage divider behavior under different loads
  • Investigating temperature effects on component behavior
  • Plotting diode forward voltage characteristics
  • Finding optimal bias points for your design

Using DC Sweep in Breadpad #

Setting Up the Analysis #

  1. Build your circuit on the breadboard
  2. Place probes at points where you want to measure the output
  3. Select a voltage source or component to sweep
  4. Open the oscilloscope and select “DC Sweep” from the oscilloscope menu

Configuring Parameters #

  • Sweep Source: Select the voltage source or component parameter to vary
  • Start Value: The minimum value for the sweep
  • Stop Value: The maximum value for the sweep
  • Step Size or Number of Points: Controls the resolution of the sweep
  • Output Nodes: Select which probe points to monitor during the sweep

Running the Analysis #

  1. Click “Run Simulation” to perform the DC sweep
  2. Results are displayed as a graph with:
    • X-axis: The swept parameter (e.g., input voltage)
    • Y-axis: The measured output (voltage or current)

Interpreting Results #

  • The slope of voltage transfer curves indicates gain
  • Flat regions may indicate saturation or cutoff
  • Intersections with reference lines can show threshold points
  • Multiple traces can be compared to analyze different circuit nodes

Advanced Features #

  • Multiple Sweeps: Run consecutive sweeps with different parameters
  • Nested Sweeps: Vary two parameters simultaneously (Premium feature)
  • Temperature Sweeps: See how circuit behavior changes with temperature
  • Parametric Analysis: Sweep component values to optimize performance
  • Export Data: Save sweep results as CSV for further analysis

Example: Transistor IV Curves #

To generate IV curves for a BJT transistor:

  1. Build a circuit with a variable voltage source connected to the collector
  2. Add a second voltage source for the base
  3. Place probes to measure collector current
  4. Configure a DC sweep of the collector voltage (e.g., 0V to 5V)
  5. Run multiple sweeps with different base current values
  6. The resulting family of curves shows the transistor’s operating characteristics

Tips for Effective DC Sweep Analysis #

  • Start with wide sweep ranges and coarse steps, then refine for areas of interest
  • Use logarithmic sweeps for parameters that span several orders of magnitude
  • Compare simulation results with component datasheets to verify proper operation
  • Save and export sweep configurations to maintain consistent test conditions
  • For non-linear devices like diodes and transistors, use smaller step sizes near transition points

Troubleshooting DC Sweep Issues #

If you encounter problems with DC sweep analysis:

  1. Verify that the swept source is properly connected in your circuit
  2. Check that sweep ranges are appropriate for your components
  3. Ensure adequate power supply voltages for active components
  4. For convergence issues, try adding small series resistances to semiconductor devices
  5. Use smaller step sizes in regions with rapid changes

DC sweep analysis is an excellent way to characterize your circuit’s behavior across a range of operating conditions without repeatedly modifying your physical circuit.