Designing for Efficiency: A look at DC-to-DC Converters

The use of energy-efficient devices within your designs can help minimize environmental impact. With simulation, you can easily determine how energy-efficient a device is to optimize your designs before you get them on the market. For example, let’s compare the efficiency of Silicon (Si) and Silicon Carbide (SiC) devices within a push-pull DC-to-DC converter circuit containing a UC1846 PWM controller and simulate it with PSpice. To access the project files,  fill out the form at the bottom of this blog. This project includes two schematic designs with identical circuits, except for the following differences:

• Si_devices: MOSFET –  IRFP27N60K and diode – 1N1190
• SiC_devices: MOSFET – SCT4045DE and diode – STPSC20065W

Within the project, select the Si_devices schematic; here, you’ll see that the controller drives the two MOSFETs present at the input of the transformer ‘XFMRAUX.’ By running the Si_devices-trans simulation, you’ll see plot windows with multiple traces, as shown in Figure 1. The simulation is configured to display steady-state results, so it may take a short while to complete, but you can easily monitor the progress within the simulation status window. Here’s what’s displayed:   

• The plot at the top shows the overall efficiency of the circuit using trace expressions. To calculate the efficiency at a steady state, place one cursor at 4.86 ms and the other at 4.9 ms.
• The other four plots have trace expressions to calculate input-output power, diode loss, switch loss, and output voltage and current.

Figure 1. Transient analysis simulation of a push-pull converter displaying plots for efficiency, input-output power, diode loss, switch loss, and output voltage and current

Record the measurement results for the Si devices. To run the circuit with the SiC devices, find the simulation profile drop-down within the Capture window and select SiC_devices-trans. This will activate the schematic with the SiC MOSFETs and diodes. Open the schematic page and run the simulation to see the results.

Figure 2. Simulation profile drop-down within OrCAD Capture

To access saved plot displays in PSpice, select Window > Display Control from the menu. In this project, the plot display with all the trace expressions is saved as loss_eff_calc.

Based on the results of both simulations, by simply replacing four Si devices with their SiC alternatives, the calculation shows an increase in efficiency by more than 7.6%. This is equivalent to real-world energy savings as listed below: 

• Switching loss savings of ~10.6 W. 
• 12-hour daily operation savings= 128 Wh
• Yearly savings = 46.72 kWh 
• For 1 million devices installed worldwide = ~47 million units of electricity saved yearly 

Fill out the form to download the example.