SiC Power Device｜Application
About Surges in Gate-Source Voltages
2022.12.21
Points of this article
・In recent years, SiC MOSFETs have been used increasingly frequently in power supply and power line switching applications, but they are so fast that the effects of the self inductance of the package of the MOSFET and that of peripheral circuits wiring cannot be ignored.
・For this reason, unexpected surges sometimes occur in the gate-source voltage in particular, and these must be addressed.
Power semiconductors such as MOSFETs and IGBTs are used as switching elements in various power supply applications and power lines. Among these devices, SiC MOSFETs have been used more and more frequently in recent years, and operate so rapidly that the effects of the inductance of the package of the MOSFET itself and the wire self inductance of peripheral circuits on changes in voltage and current during switching cannot be ignored. In particular, when the voltage or current of the device itself changes, unexpected surges may occur in the gate-source voltage, necessitating special measures. Here we examine and consider such measures. Surges occurring in gate-source voltages are explained in detail in “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, which the reader is invited to consult.
About Surges Occurring in Gate-Source Voltages
The circuit diagram on the right is the simplest synchronous boost circuit that uses MOSFETs in a bridge configuration. In this circuit, the high side (hereafter HS) SiC MOSFET is switched in synchronization with switching of the low side (LS) SiC MOSFET. When the LS turns on, the HS turns off, and when the LS turns off the HS turns on, in alternating on/off operation.
Through this switching, surges occur not only on the switching LS, but also on the synchronized HS according to changes in the voltage and current on the switching LS.
The waveform diagram below shows the waveforms of the drain-source voltage (VDS) and the drain current (ID) upon LS turn-on and turn-off in the circuit, as well as the behavior of the gate-source voltage (VGS). The horizontal axis represents time, and time intervals Tk (k = 1-8) are defined as follows.
T1: Interval during which LS is on and the SiC MOSFET currents are changing
T2: Interval during which LS is on and the SiC MOSFET voltages are changing
T3: Interval during which LS is on
T4: Interval during which LS is off and the SiC MOSFET voltages are changing
T5: Interval during which LS is off and the SiC MOSFET currents are changing
T4 to T6: Dead time interval until HS turns on
T7: Interval during which HS is on (synchronous rectification interval)
T8: Dead time interval from turn-off of HS to turn-on of LS
Phenomena (I) to (VI) indicated by arrows occur in the gate-source voltage VGS. The broken lines represent the original waveforms without surges. These phenomena occur for the following reasons.
Phenomena (I), (VI) → Change in drain current (dID/dt)
Phenomena (II), (IV) → Change in drain-source voltage (dVDS/dt）
Phenomena (III), (V) → End of change in drain-source voltage
Among these phenomena, the gate-source voltage surges that we will examine here are the phenomenon (II) occurring on the HS upon LS turn-on, and the phenomenon (IV) occurring on the HS upon LS turn-off, which particularly affect device operation.
【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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