Step into the future of power electronics where SiC SBDs revolutionise efficiency and performance in high-power applications.
In the rapidly evolving field of power electronics, Silicon Carbide Schottky Barrier Diodes (SiC SBDs) are establishing themselves as superior alternatives to traditional silicon-based diodes in high-power applications such as Interleaved Power Factor Correction (IPFC) systems [1]. These diodes utilise the exceptional properties of silicon carbide, offering a substantial performance enhancement over traditional Silicon Fast Recovery Diodes (Si FRDs) [2].
Among the advantages of SiC SBDs are their ability to operate at higher temperatures, lower forward voltage drop levels, almost instantaneous reverse recovery, and a significantly reduced reverse recovery current [3]. These features not only increase efficiency and flexibility in designing applications but also encourage the development of more compact and cost-effective solutions. In a 3.6 kW IPFC system, as shown further, the use of SiC SBDs over Si FRDs significantly enhances system efficiency, impacting switch losses, thermal behaviour, reverse recovery, and overall performance.
As technological advancements progress, the importance of SiC SBDs in the realm of power electronics continues to grow. These diodes are increasingly seen as vital components in modern electrical and electronic engineering applications, improving both performance and efficiency. Their design, which promotes the movement of majority charge carriers, contrasts with that of traditional silicon-based diodes that rely both on minority and majority charge carriers, leading to inefficiencies such as slower operation and greater energy loss.
Additionally, the lower breakdown voltages of the conventional Si FRDs restrict their usages in high-power designs. In contrast, SiC SBDs, with their superior dielectric breakdown field strength, are capable of handling significantly higher voltages—up to 1200V, and prototypes that can withstand voltages even up to 1700V are currently under development. This robust capacity makes SiC SBDs highly advantageous in settings that demand high voltage and efficiency, positioning them as the preferred choice for cutting-edge power electronics applications.
SiC SBDs: Comparison with Si FRDs
SiC SBDs offer significant enhancements over Si FRDs, especially in terms of reverse recovery performance, which is crucial for high-speed switching applications. One of the standout features of SiC SBDs is their ability to operate at higher temperatures. This characteristic is particularly valuable in power electronics applications that are subjected to high thermal loads, ensuring reliability and stability under stressful conditions.
Also, as SiC SBDs boast a lower forward voltage drop, a feature that significantly reduces energy dissipation during operation, thus boosting the overall efficiency of the system. This rapid response is critical in applications that require high-speed switching, enhancing both performance and efficiency [4, 5 and 6]. The SiC SBDs are characterised by their very low reverse recovery currents, which help minimise the risk of performance degradation and energy waste during the reverse recovery phases. The above property is particularly beneficial in reducing losses and improving the overall operational efficiency of power systems. Collectively, these attributes make SiC SBDs a superior choice for modern electronic applications that demand high performance and efficiency.
These benefits not only enhance the efficiency of SiC SBDs but also offer designers greater flexibility in increasing switching frequencies. This translates into smaller, more cost-effective solutions for magnetic components, pushing forward the boundaries of what is possible in power electronics design. The efficiency and adaptability of SiC SBDs highlight their importance in modern electronic and electrical engineering, making them a key component in the ongoing evolution of technology in this field.
Necessity of SiC SBDs in Power Factor Correction circuits
Power Factor Correction (PFC) circuits are essential for improving the efficiency of power supplies by shaping the input current to be in phase with the input voltage, thereby maximising the real power available from the mains. Different conduction modes in PFC circuits offer varied benefits and are suitable for specific applications. These modes include:
Continuous Conduction Mode (CCM). CCM is characterised by comparatively low peak currents and no zero current switching at higher currents. This mode is highly efficient at higher power levels, producing low current harmonics. However, it has high ripple, though less than that in the Discontinuous Conduction Mode.
Discontinuous Conduction Mode (DCM). DCM offers zero current switching and is known for its high efficiency at light loads. While it produces higher peak currents than that in the CCM, it also results in higher current harmonics. However, DCM provides an easy control scheme, making it favourable for certain applications.
In high-power circuits, CCM is generally preferred due to its association with lower peak and RMS currents. This preference enhances the system’s efficiency and reduces thermal stress on components. Within this context, the SiC SBD emerges as an optimal choice for several reasons as explained below.
ROHM SiC SBDs are renowned for their exceptional performance in reducing switching losses, which is a common issue in PFC circuits operated under CCM. Traditional Si FRDs are expected to exhibit substantial switching losses during diode turn-off due to poor reverse recovery. This not only impacts efficiency but also shortens the lifespan of the power device.
The reverse recovery current peak in SiC SBDs is significantly lower than that in Si FRDs. This attribute helps in reducing the turn-on losses on the switch, further enhancing overall circuit efficiency.
In addition, the impact on switching losses is noteworthy. With almost zero injection of minority carriers, SiC SBDs virtually eliminate switching losses. This characteristic makes them highly suitable for modern high-efficiency PFC circuits operated under CCM, where minimizing energy waste is crucial.
Figure 2 and Table 1 typically illustrate the reverse recovery behaviour of SiC SBDs when compared to Si FRDs. These plots help us in understanding how SiC SBDs manage to achieve superior performance by effectively reducing the adverse effects of reverse recovery processes that are prevalent in Si FRDs.
Practical comparison of the SiC SBD against Si FRD
In a typical PFC circuit (Figure 3), the choice of diodes can significantly impact the efficiency and performance of the system. A practical comparison between Si FRDs and SiC SBDs elucidates the advantages of using SiC based SBDs in a high-power setting. This comparison is obtained through an experiment that focuses on a 3.6 kW IPFC system equipped with a ROHM Field Trench Insulated Gate Bipolar Transistor (IGBT), model RGWX5TS65D, rated at 650V, 75A.
The respective Si FRD and SiC SBD (SCS230AE2) used in this experiment are both products of ROHM, rated at 600V, 30A. These diodes play crucial roles in the IPFC system’s performance, affecting several key aspects:
Switch Losses. The efficiency of the switch directly correlates with the performance of the diode used in the system, particularly in terms of how effectively it can handle power and minimise losses.
Thermal Behaviour. The ability of the diode to manage heat affects the overall thermal performance of the switch, influencing its reliability and lifespan.
Reverse Recovery. The speed and efficiency with which a diode can handle reverse currents impact the overall efficiency and operational stability of the IPFC system.
System Efficiency. Ultimately, the choice of the diode used in the system influences the overall efficiency of the 3.6kW IPFC system, which is crucial for high-performance applications.
| Enhanced IPFC System Features and Specifications |
| Key Enhancements: Interleaved Operation: Increases system efficiency. Robust Protection Features: Input Over-Voltage Protection (OVP) Under-Voltage Protection (UVP) Input Short-Circuit (SC) Protection Performance Specifications: Input Voltage: 180V to 300V AC Input Frequency: 47Hz to 60Hz Output Voltage: Adjustable from 360V to 410V DC Output Current: 8.54A to 10.50A Output Power: 3500W to 3780W Efficiency Range: 95 – 97% Total Input Power: 3684W to 3897W Power Factor: 0.99 under typical conditions Board Dimensions: 177mm x 140mm x 70mm Critical ROHM Components in the IPFC system: IGBT (RGWX5TS65D): Main switch of the IPFC system. Boost Diode (SCS230AE2): Boosts phase efficiency. Gate Driver (BD2310G): Controls gating signals. DC-DC Converter IC (BM2P063HK-LBZ): Manages DC to DC conversion. These enhancements and specifications ensure the IPFC system’s reliable operation under various electrical conditions. |
Switch Losses
Losses in IGBTs (Figure 4), which are crucial components in power electronics, can significantly affect the performance and efficiency of the entire IPFC system. These losses can be mainly categorised into three types:
Conduction Losses (Pcond). These occur when the IGBT is in the on-state, allowing current to flow through it. The losses are formulated as follows:
where is the collector-emitter voltage in the on-state, I is the current flowing through the IGBT and is the resistance.
Switching Losses (Psw). These include both turn-on and turn-off losses, pivotal during the transitions of the IGBT’s operating states. The losses can be quantified as follows:
Blocking/Leakage Losses (Pb). Typically negligible, these losses occur when the IGBT is in the off-state and functions to block voltage.
Turn-On Energy
The role of diodes in controlling the switching behaviour and efficiency of IGBTs in PFC circuits is critical. A practical comparison, as demonstrated in Figure 5 that highlights the difference between turn-on energy losses of Si FRDs and SiC SBDs.
As seen in Figure 5, the Si FRD exhibits a significant increase in turn-on energy losses,
approximately 60%–70% under typical conditions, escalating to almost 90% at full load. Such high losses underscore the inefficiency of Si FRDs in high-performance applications.
In contrast, the SiC SBDs show significantly lower turn-on energy losses, emphasising their
suitability for efficiency-critical applications such as PFC design. The reduced energy loss during switching phases enhances the overall system performance, leading to better thermal
management and increased longevity of the IGBT.
Thermal Performance
In the field of power electronics, understanding and managing the junction temperature of semiconductor devices such as IGBTs is crucial for ensuring their performance and longevity. The junction temperature (Tj) is calculated by considering the total losses within the device as follows:
Components of Thermal Resistance
Junction Temperature
The practical measurement of the junction temperatures was performed using the switching data captured in the experiment. Table 2 shows the measured junction temperatures at various loads respectively for the Si FRD and the SiC SBD setup.
*Note: The Tj* values of the switch with Si FRD for loads >3kW are calculated values as temperatures at 3kW are nearing Tj(max) already.
The comparison clearly demonstrates that the use of SiC SBDs in a PFC application significantly reduces the junction temperatures under all measured loads. This reduction in temperature translates to various benefits:
Improved Power Density. Lower temperatures allow for more power handling capacity within the same physical space.
Enhanced Converter Efficiency. Lower junction temperatures correlate with lower energy losses and higher efficiency.
Extended Usability of Switch. The same switch can operate at higher power ratings without exceeding its thermal limits, thus extending its practical usability and reducing the need for frequent replacements.
Total Loss and Efficiency
In the experiment mentioned above, we explore the performance of an IPFC system using two different diodes. This comparison focuses on the total loss and efficiency of the system across various load conditions, highlighting how each diode type affects the overall performance and reliability of the IPFC system. This detailed evaluation seeks to provide insights into the superior thermal and electrical properties of these diodes and their impact on system efficiency.
Performance data of the IPFC system with Si FRD vs SiC SBD
The performance of an IPFC system significantly impacts its efficiency and reliability. In this experiment, we compare the performance of an IPFC system using two different diodes: Si FRD and SiC SBD (SCS230AE2). The data focuses on the total loss and efficiency of the system at various load conditions, providing a comprehensive understanding of how each diode influences the performance of the IPFC system.
Efficiency comparison
The graph in Figure 8 plots the efficiency of the IPFC system using both types of diodes across a range of operating conditions. Efficiency is a critical metric as it directly correlates with energy conservation and system performance. The expectation that the SiC SBD, with its lower forward voltage drop and higher temperature tolerance, would demonstrate higher efficiency, is validated through the results depicted in blue curve.
Loss comparison
Figure 9 shows the total power losses when using the Si FRD as compared to the SiC SBD. Power losshows the total power losses when using the Si FRD as compared to the SiC SBD.
Power losses not only affect the efficiency but also impact the thermal management of the device, which is vital for maintaining the longevity and reliability of the system. Lower losses are preferable as they reduce the thermal strain on the system and potentially lower cooling requirements.
Diode Reverse Recovery
In high power applications, especially in PFC circuits, the choice of the diode significantly impacts the overall system performance. A practical comparison between the reverse recovery characteristics of SiC SBDs and Si FRDs reveals critical insights. This experiment focuses on the performance of these diodes under a full load condition of 3.6 kW.
Figures 10 and 11 illustrate the reverse recovery characteristics of the SiC SBD and Si FRD
respectively. A close analysis of these results, along with additional data from Figures 6 and 7 highlights the significant differences between the SiC SBD and Si FRD.
Charge Recovery. The SiC SBD exhibits a substantially lower charge recovery than that of the Si FRD, indicating a more efficient performance during the reverse recovery phase.
Reverse Recovery Current. The peak reverse recovery current in the SiC SBD is nearly six times lower than that in the Si FRD under the same 3.6 kW load. This reduction is crucial as it directly correlates with reduced thermal stress and lower energy dissipation.
In the field of power electronics, particularly in IPFC applications, the comparison between the experimental results of SiC SBDs and Si FRDs underscores the distinct advantages of SiC SBDs. These include enhanced efficiency, reduced switch losses, superior thermal management, and lower electromagnetic interference. With their ability to handle higher voltages and provide near-zero reverse recovery, SiC SBDs not only improve the performance and reliability of high-power circuits but also contribute to the development of more compact and energy-efficient power systems. Thus, the clear benefits demonstrated by SiC SBDs in practical and theoretical evaluations make them a preferred choice for efficient power converters. Silicon Carbide (SiC) Schottky Barrier Diodes (SBDs) demonstrate significant advantages over traditional Silicon (Si) diodes in terms of efficiency and is the preferred choice for high density power supplies [7]. ROHM portfolio of SiC SBDs are summarized in Table 3 and can be found as included in [8].
| Advantages of SiC SBDs in PFC Circuits |
| When deploying SiC SBDs over Si FRDs in PFC circuits, especially in high-power applications, several key benefits of using SiC SBDs are observed: Enhanced Efficiency: SiC SBDs exhibit lower charge recovery and significantly reduced reverse recovery currents, leading to heightened overall efficiency in PFC circuits. Reduced Switch Losses: The minimal reverse recovery currents place less strain on switching components, effectively reducing switch losses and enhancing component longevity. Superior Recovery Performance: SiC SBDs provide faster and more efficient recovery in high-power scenarios, which improves both the response times and the reliability of the circuit. Decreased Reverse Recovery Current: The reduced peak reverse recovery current lowers the risk of overheating and potential damage, ensuring stable circuit operations under demanding conditions. Lower Electromagnetic Interference (EMI)/Electromagnetic Compatibility (EMC): With lower peak reverse recovery current, SiC SBDs ensure reduced electromagnetic interference, making them suitable for sensitive applications where maintaining low EMI/EMC is crucial. Thus, these advantages make SiC SBDs a preferable choice for modern high-power PFC applications, offering improved performance and reliability. |
References
[1] ROHM’s SBD Lineup Contributes to Greater Miniaturization and Lower Loss in Automotive, Industrial, and Consumer Equipment: ROHM White Paper, 2024.
[2] How to Select Rectifier Diodes, ROHM Application Note, 66AN017E, Nov. 2023.
[3] Basics of SiC Power Devices, ROHM Tech Web Handbook, TWHB-16e_001, 2023.
[4] Silicon Carbide Schottky Barrier Diodes Taking Efficiency to the Next Level for PFC and Other Applications, ROHM White Paper
[5] Advantages of YQ Series: Compact and Highly Power Conversion Efficiency Schottky Barrier Diodes for Automotive, ROHM Application Note, 64AN107E, Sep. 2023
[6] Advantages of PMDE Compact Package with High Heat Dissipation for Automotive Schottky Barrier Diodes, ROHM Application Note, 63AN130E, Apr. 2022
[7] SiC Power Devices and Modules Application Note, No. 63AN102E Rev.003, 2020 [8] ROHM SiC Schottky Barrier Diodes
