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Optimize Power Systems Using SiC MOSFET and Si IGBT Gate Drives

By: DigiKey's North American Editors 2023-07-25

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Silicon carbide (SiC) MOSFETs and silicon (Si) IGBTs are key components in the DC-DC converters, battery chargers, motor drives, and alternating current (AC) inverters required for green energy applications like electric vehicles (EVs) and photovoltaic (PV) systems. However, if you want to get maximum efficiency, the gates of SiC MOSFETs and Si IGBTs need precise drive voltages when turning on and off, depending on the device used. And to deliver high reliability, you need gate drivers with reinforced insulation, high isolation voltages, common mode transient voltage immunity (CMTI), low isolation capacitances, electromagnetic compatibility (EMC) including CISPR 32 55032 for emissions, and IEC 61000-4-2 for immunity, short circuit protection, and an operating temperature range of -40 to +105°C.

These numerous performance demands make designing compact, high-efficiency DC-DC converters suitable for driving the gates of SiC MOSFETs and Si IGBTs a daunting and time-consuming challenge.

To speed things up and realize dependable, compact, and efficient solutions, you can instead use off-the-shelf gate drive DC-DC converters. These converters deliver the precise voltages needed to support high-efficiency switching and satisfy the operational demands to ensure high reliability.

Let’s review the different drive voltage needs of SiC MOSFETs and Si IGBTs, examine more closely the key specifications, and look at some gate drive DC-DC converters from Mornsun that you may find suitable for use in a range of green energy systems.

Drive voltage variations

Si IGBTs and SiC MOSFETs both offer low conduction losses and can be used for high-efficiency power conversion applications. For high-frequency applications, SiC MOSFETs can offer lower overall switching losses, including turn-on and shutdown losses. Specifically, the turn-on losses for SiC MOSFETs are typically 15% to 20% lower than Si IGBTs, and the shutdown losses are lower by 75%. The higher shutdown losses in Si IGBTs result from tail currents during turn-off that increase power dissipation. SiC MOSFETs do not experience a tail current.

The difference in the turn-on and shutdown characteristics of SiC MOSFETs and Si IGBTs results in different drive voltage needs (Table 1).

Table 1: Different switching characteristics result in different drive voltage needs. (Table source: Mornsun)

Key drive power specs

While the turn-on and shutdown drive voltage requirements of Si IGBTs and SiC MOSFETs differ, their driver power supplies have similar performance requirements in other areas, including:

Reinforced insulation, creepage and clearance distances, and a continuous insulation voltage of 1,700 volts for compliance with IEC 61800-5-1, which can be difficult to achieve while maintaining a compact and efficient solution.
A high CMTI. This is the maximum allowable rate of rise or fall of the common-mode voltage between two isolated circuits, measured in kilovolts per microsecond (kV/μs). Both device types need to support high-frequency designs and faster switching transitions, helping to achieve smaller system sizes and higher efficiency.
Isolation capacitance should be low. If it’s too high, common-mode interference can affect the pulse width modulation (PWM) control signal, resulting in a signal error and system failure.
EMC performance that meets the limitations of CISPR 32/EN55032 for susceptibility and IEC/EN61000-4-2 for immunity is required to ensure reliable system operation.

Short circuits are one of the most common failure modes in power converters. As such, gate drive power supplies need to include short-circuit protection.

Gate drive power supplies

If you’re designing green energy systems using SiC MOSFETs, you can turn to the QAxx3C-R3 series of DC-DC converter modules from Mornsun. These gate drive power supplies are available with input voltages of 5, 12, 15, and 24 volts DC (VDC), and a variety of output combinations like the QA123C-2005R3 that has a 12 VDC input and produces drive voltages of 20 and -5.0 VDC, the QA243C-2005R3 with a 24 VDC input and 20 and -5.0 VDC outputs, and the QA153C-1504R3 (Figure 1) with a 15 VDC input and outputs of 15 and -4.0 VDC.

Figure 1: The QA153-1504R3 is a SiC MOSFET drive power module with an input of 15 VDC and outputs of 15 and -4.0 VDC. (Image source: Mornsun)

If you’re using IGBTs, Mornsun offers the QAxx3H-R3 series with input voltages of 12, 15, and 24 VDC. The QA123H-1509R3, for example, has a 12 VDC input and produces outputs of 15 and -9.0 VDC. There’s also the QAxx3-R3 series with input voltages of 5, 12, 15, and 24 VDC. The QA053-1509R3, for example, has an input voltage of 5 VDC and outputs 15 and -8.7 VDC.

Common features of all three series of these drive power supplies include:

Efficiency up to 87%
Single-in-line package (SIP)
Reinforced insulation tested at 5 kVAC for 1 minute with maximum leakage of 1 milliampere (mA)
Continuous insulation voltage of 1,700 volts
CMTI of ±200 kV/μs
Isolation capacitance of 3.5 picofarads (pF)
EMC compatibility, including CISPR 32 55032 for emissions and IEC 61000-4-2 for immunity with external components
Short circuit protection
-40 to +105°C operation

Application examples

The QAxx3C-R3, QAxx3-R3, and QAxx3H-R3 series drive power supplies are highly integrated and require only three 100 microfarad (µF), 35 volt low-resistance electrolytic capacitors for general applications (Figure 2), and a few additional components for typical EMC requirements (Figure 3 and Table 2).

Figure 2: Capacitors C1, C2, and C3 are all 100 µF, 35 volt devices in both IGBT and SiC applications (shown above). (Image source: Mornsun)

Figure 3: EMC component values vary based on the input voltage (Table 2). CY1 (bottom) is a 330 pF capacitor used only with 5 VDC input models. (Image source: Mornsun)

Table 2: Component values to support EMC performance. (Table source: Mornsun)

Conclusion

Selecting the gate drive power supply is an important step when optimizing the efficiency and reliability of Si IGBT and SiC MOSFET power converters for green energy applications like PV systems and EVs. Mornsun offers several families of DC-DC converter modules with a selection of input and output voltage options that can be used to drive a wide range of Si IGBTs and SiC MOSFETs.