SHYSEMI:Application and Performance Analysis of SiC Schottky Diodes in Boost-Type PFC Circuits

Table of Contents:

1. Introduction

2. Experimental Setup and Test Conditions

3. Results and Discussion

4. Extended Validation in Low-Power PFC Circuits

5. Conclusion

6. Summary and Outlook

Keywords:

SiC Schottky Diode, Fast-recovery silicon diode(FRD), Switched-Mode Power Supplies (SMPS), PFC Circuit, Reverse Recovery Characteristic

1. Introduction

Switched-mode power supplies (SMPS) are integral to modern electronic systems such as computer power units, industrial drives, communication infrastructure, and renewable energy systems. To achieve higher power density and conversion efficiency, manufacturers increasingly seek to raise switching frequencies in PFC circuits. However, in Continuous Conduction Mode (CCM) Boost-type PFC topologies, the reverse recovery current of silicon diodes leads to considerable switching losses, parasitic oscillations, and EMI issues—limiting the practical upper frequency of operation.

SiC Schottky diodes offer a compelling solution. As majority-carrier devices with negligible reverse recovery charge, wide bandgap material properties, and superior thermal conductivity, they enable higher switching frequencies, reduced losses, and enhanced reliability compared to silicon-based counterparts. SHYSEMI will focus on analyzing the performance of silicon carbide Schottky diodes in boost power factor correction circuits.

2. Experimental Setup and Test Conditions

2.1 Circuit Configuration

The experimental PFC circuit, shown in Figure 1, adopts a standard Boost topology. The switching transistor (VT) is a MOSFET (model: IPW60R045CP, rated 600 V / 60 A).

Figure 1 Boost (Boosting) type PFC circuit

Two diodes were evaluated under identical conditions:

Test specifications:

The test prototype operated at 50 kHz when using the silicon diode, while the SiC diode version was tested at switching frequencies of 50 kHz, 100 kHz, 150 kHz, and 200 kHz for comparative evaluation.

3. Results and Discussion

3.1 Efficiency Improvement and Power Loss Distribution

At 50 kHz operation, replacing the silicon diode with a SiC Schottky diode improved the system efficiency from 94.36% to 95.05%, corresponding to a reduction of approximately 28 W in total power loss.
Since the forward voltage drop of both devices is similar, this reduction can be attributed primarily to the elimination of reverse recovery loss.

Power loss analysis (illustrated in Figure 2) shows that, in the silicon diode configuration, reverse recovery loss accounts for roughly 45% of the total switching device loss. Moreover, this loss component increases nearly linearly with switching frequency, confirming that diode recovery characteristics are the dominant factor constraining high-frequency operation in CCM-PFC circuits.

Figure 2 Loss Distribution of Switching Devices

3.2 Junction Temperature Behavior

Device junction temperatures were measured under an ambient temperature of 40 °C (Table 1).

Table 1 Junction Temperatures of Devices at Different Frequencies (Environmental Temperature: 40℃)

The SiC diode exhibited only a marginal temperature increase with frequency, whereas the MOSFET junction temperature rose significantly as switching frequency increased.
This indicates that, once the SiC SBD is adopted, the majority of switching loss originates from the MOSFET rather than the diode.
When reverse recovery loss is effectively eliminated, frequency-dependent losses represent only about 14.5% of the total system loss, confirming the superior thermal stability of the SiC-based design.

Table 3 Junction Temperatures of Devices at Different Frequencies (Environmental Temperature: 40℃)

3.3 System Efficiency Across Frequency Spectrum

As shown in Figure 4, the highest overall system efficiency was achieved at 100 kHz, followed by 50 kHz, with a slight drop at 150 kHz.
This trend can be explained by the fixed inductor design parameters. As frequency increases, current ripple across the inductor decreases, thereby reducing semiconductor losses. However, due to nonlinear inductor core and copper losses, an optimal frequency point exists where overall efficiency peaks. For this prototype, the optimal operating frequency was found to be approximately 100 kHz.

Figure 4 Efficiency of the prototype under different frequencies

4. Extended Validation in Low-Power PFC Circuits

A secondary set of experiments was conducted on a 300 W Boost-PFC prototype with a DC output voltage of 380 V, nominal frequency of 70 kHz, and wide input range of 90–260 V, using the same topology for comparative evaluation.

Tested diodes:

4.1 Switching Waveform Analysis

As illustrated in Figure 5, during MOSFET turn-on transitions, the peak reverse current was significantly lower when using the SiC diode compared with both silicon counterparts. This confirms the superior recovery behavior of the SiC SBD—virtually eliminating reverse recovery current and minimizing switching stress on the MOSFET.

Figure 5 Voltage and current waveforms during the switching of the MOSFET transistor.

a) SDP04S60 (SiC diode) b) STTH5R06D diode c) RURD460 diode

4.2 Efficiency and EMI Performance

Measured efficiency data under 220 V and 110 V input conditions (Tables 2 and 3) demonstrate that the SiC diode achieved the highest efficiency across all test cases.
Although the forward voltage of SiC diodes is typically higher than that of silicon diodes such as RURD460, the elimination of reverse recovery losses dominates, leading to overall lower total power dissipation in CCM-PFC operation.

Table 2 Efficiency Measurement Values at Input Voltage of 220V

Table 3 Efficiency Measurement Values at Input Voltage of 110V

Conducted EMI measurements (Figure 6) reveal that, within both the 150 kHz–1 MHz and 1–30 MHz frequency bands, the SiC diode configuration generated substantially lower noise injection levels compared to silicon alternatives, thereby simplifying EMI filter design.

Figure 7: Measured waveforms of conducted EMI at 220V input voltage

a) in the range of 150kHz to 1MHz b) in the range of 1 to 30MHz

5. Conclusion

The experimental results confirm that adopting SiC Schottky diodes in PFC boost converters provides substantial system-level benefits:

Significant Reduction of Switching Losses
– Reverse recovery loss is nearly eliminated, reducing total switching device losses by up to 45%.

Enhanced Efficiency and Thermal Stability
– System efficiency increases by approximately 0.7%, while device junction temperatures remain lower and more stable under high-frequency operation.

Superior EMI and Reliability Performance
– Reduced reverse recovery current and dv/dt-induced ringing effectively minimize conducted and radiated noise.