SiC Power Device｜Application
SiC MOSFETs： Snubber Circuit DesignsTypes and Selection of Snubber Circuits
2024.09.25
Points of this article
・In order for a snubber circuit to be maximally effective, it must be mounted as close as possible to the switching device.
・Snubber circuits include circuits that are combinations of passive components such as resistors, inductors, and capacitors (R, L, C), as well as active circuits using semiconductor devices.
・In this article, C snubber circuits, RC snubber circuits, discharge RCD snubber circuits, and non-discharge RCD snubber circuits are introduced as circuit designs that do not require control and are attractive with respect to cost.
This is the second explanation relating to the types and selection of snubber circuits.
- Surges occurring between drain and source
- Types and selection of snubber circuits
- C snubber circuit design
- RC snubber circuit design
- Discharge RCD snubber circuit design
- Non-discharge RCD snubber circuit design
- Difference in surge occurrence depending on package
Types and Selection of Snubber Circuits
Snubber circuits include both circuits that are combinations of passive components such as resistors, coils, and capacitors, and active circuits that use semiconductor devices (*1). This article explains circuit designs that do not require control and are advantageous in terms of cost.
Fig. 5 shows examples of snubber circuits. These include (a) a C snubber circuit in which a capacitor CSNB connects together upper and lower SiC MOSFETs in a bridge configuration, (b) an RC snubber circuit in which a resistor RSNB and capacitor CSNB are connected between the drain and source of each switching device, (c) a discharge RCD snubber circuit in which a diode is added to an RC snubber circuit, and (d) a non-discharge RCD snubber circuit in which the discharge path of the RCD snubber circuit is changed.
In order for these snubber circuits to be sufficiently effective, they must be mounted as close to the switching device as possible.
In the case of (a), the C snubber circuit, although the number of components is small, they must be connected at the upper and lower parts of a bridge configuration, and so there is the drawback that wiring lengths are increased. These circuits are typically used more often in modules with 2-in-1 configurations and the like, as opposed to discrete configurations.
In (b), the RC snubber circuit, the snubber circuits are located near the switching devices, but each time the devices turn on, all the energy accumulated in the capacitors CSNB must be consumed in the resistors RSNB (in the case of a bridge configuration, on the synchronous side the energy accumulated in CSNB during the dead time period is recovered). Hence when the switching frequency is high, the power consumed in RSNB can be as high as several watts, which limits the size of CSNB, and so when using this method, the surge suppression effect tends to be limited. Moreover, the surge absorption ability is limited by RSNB, and so once again, the suppression effect is often limited.
In (c), the discharge RCD snubber circuit, the resistor RSNB dissipates as much as the RC snubber circuit of (b); but because surges are absorbed through only a diode the surge absorption effect is higher than in (b), making such circuits more practical. However, attention must be paid to the recovery characteristics of the diodes used, and because there is a large change in current during surge absorption, the wiring inductance of the snubber circuits must be made as small as possible, among other matters. Operation is the same even when RSNB is connected in parallel with CSNB.
In the case of (d), the non-discharge RCD snubber circuit, only surge energy absorbed in CSNB is dissipated in RSNB; all the energy accumulated in CSNB is not discharged each time switching occurs. Consequently, the power dissipated in RSNB does not increase so very much even when the switching frequency is raised, and CSNB can be made larger, so that a circuit with an extremely powerful suppression effect can be obtained. However, the wiring layout is more complex, and this circuit can be implemented only on a PCB with four or more layers.
Thus there are advantages and drawbacks to each of the snubber circuits introduced here, and so the optimal snubber circuit must be selected according to the power supply circuit configuration and the power conversion capacity. Beginning with the next article, design methods for each snubber circuit are explained.
*1: Basics of Switching Converters, K. Harada, T. Ninomiya, F. Koshi, Corona, February 1992, pages 95-107
【Download Documents】 Basics of SiC Power Devices
This handbook explains the physical properties and advantages of SiC, the differences in characteristics and usage of SiC Schottky barrier diodes and SiC MOSFETs with a comparison to Si devices, and includes a description of full SiC modules with various advantages.
SiC Power Device
Basic
- What are SiC Schottky barrier diodes? ? Introduction
- What are SiC-MOSFETs? – SiC-MOSFET Features
- What are Full-SiC Power Modules?
- Summary
- Introduction
- What is silicon carbide?
Application
-
Introduction
- SiC MOSFET Bridge Configuration
- SiC MOSFET Gate Driving Circuit and Turn-On/Turn-Off Operation
- Currents and Voltages Occurring Due to Switching in Bridge Circuits
- Behavior of the Gate-Source Voltage During Low-side Switch Turn-on
- Behavior of the Gate-Source Voltage During Low-side Switch Turn-off
- Summary
- SiC MOSFETs: Method for Determining Losses from Switching Waveforms
-
SiC MOSFETs： Snubber Circuit Designs ーIntroductionー
- Non-Discharge RCD Snubber Circuit Design
- Surges Occurring between Drain and Source
- Types and Selection of Snubber Circuits
- C Snubber Circuit Design
- RC Snubber Circuit Design
- Discharge RCD Snubber Circuit Design
- Non-Discharge RCD Snubber Circuit Design
- Differences in Surge Occurrence Depending on Package
- SiC MOSFETs： Snubber Circuit Designs ーSummaryー
- Points to Note When Measuring SiC MOSFET Gate-Source Voltages: General Measurement Methods
-
Conventional MOSFET Driving Method
- Packages Provided with Driver Source Terminals
- Differences Made by and Benefits of a Driver Source Pin
- Benefits of a Driver Source Terminal: Comparisons Using Double Pulse Tests
- Behavior of Gate-Source Voltages when in a Bridge Configuration: Behavior at Turn-on
- Behavior of Gate-Source Voltages when in a Bridge Configuration: Behavior at Turn-off
- Points to be Noted Relating to Board Wiring Layout Key Points of This Article
- Verification of Loss Reduction Using Latest-Generation SiC MOSFETs
- About Surges in Gate-Source Voltages
Product Information
- SiC Schottky Barrier Diodes
- SiC MOSFET
- SiC Power Modules
- SiC Schottky barrier diode Bare Die
- SiC MOSFET Bare Die
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