SiC Power Device｜Application
Surge Suppression Circuits
2023.04.12
Points of this article
・Positive surges in the gate-source voltage (VGS) occur on both switching and non-switching sides, but positive surges on the non-switching side (HS) during LS turn-on are particularly problematic.
・In essence, measures to suppress surges are necessary, including other surges, and so surge suppression circuits must be added.
In the previous article we briefly explained surges that occur in gate-source voltages. From this article, we address measures to deal with surge occurrences. We begin by presenting surge suppression circuits.
Surges occurring in gate-source voltages have already been explained in detail in the previously mentioned “SiC MOSFETs: Behavior of Gate-Source Voltage in a Bridge Configuration” in the Applications Edition of the Tech Web Basic Knowledge section on SiC Power Devices, and should be referenced as necessary.
Surge Suppression Circuits
As explained in the previous article, positive surges in the gate-source voltage (VGS) occur on both switching and non-switching sides, but surges are especially problematic when they occur on the non-switching side (HS: high side) during LS (low side) turn-on (phenomena II). The waveform diagram on the right is the same as one presented in the previous article.
The reason for this is that, because the switching side is already in the turned-on state, if a positive voltage surge on the non-switching side has exceeded the gate threshold voltage (VGS(th)) of the SiC MOSFET, simultaneous HS and LS turn-on occurs, and a shoot-through current flows.
However, the transconductance of SiC MOSFETs is at least an order of magnitude lower than that of Si-based MOSFETs, and so sudden excessive shoot-through currents do not flow. Consequently, even if a shoot-through current had been flowing, cooling performance is sufficient, and if the Tj(max) of the MOSFET is not exceeded, there should essentially be no problems. Even so, shoot-through currents are factors directly detracting from the efficiency of the system as a whole, and cannot be called a desirable state of affairs. Hence a circuit should be added in order to suppress any voltage surges so that insofar as possible they do not exceed the VGS(th) of an SiC MOSFET.
Below, examples of such a suppression circuit are shown. These circuit diagrams are of circuits for surge suppression that are added onto general SiC MOSFET driving circuits. Suppression circuit (a) is a circuit for when a VEE2 power supply for driving turn-off is used; suppression circuit (b) is an example of a suppression circuit when a VEE2 is not used. In both circuits, VCC2 is the power supply to drive turn-on, OUT1 is the SiC MOSFET on/off signal, OUT2 is the mirror clamp control signal, and GND2 is the driving circuit ground.
The table below indicates the functions of an add-on suppression circuit. The components shown in red in the above circuit diagrams are added.
| Effect | Symbol | Details |
|---|---|---|
| Positive voltage surge suppression | D2 (C2) | Suppresses positive voltage surges when the switching side is turned on (C2 is a bypass capacitor) |
| Negative voltage surge suppression | D3 (C3) | Suppresses negative surges on the switching and non-switching sides（C3 is a bypass capacitor） |
| Positive and negative voltage surge suppression | Q2 | Suppresses positive and negative voltage surges on the non-switching side |
| False turn-on suppression | C1 | Suppresses positive voltage surges on the non-switching side |
Normally D2 and D3 absorb pulses several tens of nanoseconds in length; because as low a voltage as possible must be used for clamping, Schottky barrier diodes (SBDs) are used. Using components with a bottom electrode type low-impedance package, such as the SOD-323FL, is even more effective.
From the next article, further details will be explained.
【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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