Generate Diode Curves with Excel and a Bench Power Supply

When you need to quickly determine the forward voltage of a power diode, use your bench power supply. A bench power supply with an accurate measurement system, such as the Keysight EDU36311A Smart Bench Essentials DC power supply, shown in Figure 1, can apply a known voltage and precisely measure its ensuing output current.


Figure 1. EDU36311A Smart Bench Essentials power supply

To test a power diode, start with a low voltage and measure the current. Then increase the voltage and measure the resulting current. After several measurements, graph the results in Excel, as shown in Figure 2.

Diode IV Curve

Figure 2. Diode voltage versus current curve

Automate the task

Excel’s VBA programming, along with Keysight’s free Connection Expert, automates this task. The Connection Expert identifies the instrument’s address and passes SCPI commands through its library to the power supply. The EDU36311A offers USB and Ethernet for simple PC connectivity. With the interface cable in place, the Connection Expert software will find the power supply and its address.

A spreadsheet including a sample program is attached to this blog.

Open the spreadsheet:

  1. Update the instrument address, the number of steps, and current limit, highlighted in the red box in Figure 3.
  2. Edit the test voltages in column A.
  3. The controls in the orange box call the VBA subroutines, starting with opening the instrument connection, running the measurement block routine, and finally closing the instrument connection.
  4. Scale and label the graph for the test diode.

Excel Spreadsheet with VBA Controls

Figure 3. Excel spreadsheet example program

If you’re interested in learning more about how the program works, check out the white paper Generate Transistor Curves with a Power Supply. It includes the code to test transistors, as well as a description of how it works.