A Double Pulse Test (DPT) circuit is commonly used to evaluate the switching energy loss of power devices such as MOSFETs. One of the parameters it assesses is the behavior during turn-on and turn-off transition times. MOSFETs can be built using different technologies, such as Silicon (Si), Silicon Carbide (SiC), and Gallium Nitride (GaN), so let’s simulate and compare how each behaves. To access the project files, fill out the form at the bottom of this blog. The design consists of 3 nearly identical DPT circuits, with each containing a different MOSFET of similar ratings:
- Si: Infineon – SPW35N60C3_L1
- SiC: Qorvo – UF3C065040K3S
- GaN: Transphorm USA – TP65H050
A MOSFET's switching losses during turn-on and turn-off are calculated by taking the integral of the voltage across the MOSFET’s drain and source pin and current flowing through the drain. This energy loss is defined by the following trace expression:
Running the simulation within PSpice launches a window with the following traces already added to the plot window:
- Voltage across the MOSFETs drain and source pin
- Currently, through the MOSFET
- Energy loss
The circuit is designed to simulate the MOSFET turn-off at ~40us and turn-on at ~50us. To calculate the energy loss during turn-off, place the red cursor (left mouse button) such that the voltage across the MOSFET is about 10% of the applied voltage, which is ~40V. Then, place the green cursor (right mouse button) such that the current through the MOSFET is 10% of the total current, which is around ~2.4A.
Figure 1 highlights and displays the voltage, current, and energy calculations within the Probe Cursor window, as seen at the bottom of the image.
Figure 1. PSpice simulation displaying voltage, current, and energy calculations for a MOSFET
Similarly, for the turn-on energy loss, keep the red cursor at 10% (~2.4A) for the current through the MOSFET and the green cursor at 10% (~40V) of the voltage across the MOSFET.
To save plot displays for traces, use the Display Control menu in PSpice, as shown in Figure 2. This reduces the effort of plotting traces or expressions for each MOSFET present in the design. To access saved displays, select Window > Display Control. Select saved display (gan, si, sic) and click
Restore to see the plot display of specific devices for quick comparison.
Figure 2. Display Control menu in PSpice where you can save plot displays for traces
Based on the simulation results, the total switching loss for each MOSFET (at 27 ⁰C) is calculated as shown below:
• Si MOSFET = 358.5 uJ
• SiC MOSFET = 272.4 uJ (~24% less than Si)
• GaN MOSFET = 100.2 uJ (~172% less than SiC)
The comparison reveals that the GaN MOSFET is the most efficient among the three, with the total switching loss being approximately 3.6 times less than the Si MOSFET and approximately 2.7 times less than the SiC MOSFET.