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Issue 5 2013 Power Electronics Europe www.power-mag.com

High Voltage Gallium NitrideDevices for InvertersGallium Nitride (GaN) devices now demonstrate higher efficiency in inverter circuits for both solar andmotor drive systems and in power supply building blocks such as the DC/DC LLC and the PFC. The articleinvestigates how GaN is making such rapid performance progress and uses test results to illustrate what isnow possible using GaN compared to recent SiC transistor performance. It then predicts futureimprovements that will continue to make GaN a more attractive alternative to either Si or SiC for highefficiency systems. Umesh Mishra and Yifeng Wu, Transphorm Inc., Goleta, USA

For the past four decades, the SiliconMOSFET designers have accomplishedgreat results in density by converting fromplanar designs to trench and thendecreasing the size of the trenches whichreduces the specific on-resistance whileincreasing the capacitance.At high voltage the super junction

devices were created to reduce the EPIportion of the conduction losses of highvoltage devices while again increasing thecapacitance and changing its characteristicsin the circuit. Subsequent generations ofsuper junction devices minimized thiscapacitance problem in hard switchedapplications. Subsequent generationsfocused on either hard switched or softswitched in order to optimize theperformance trade-offs specifically for thatapplication. While recent improvements insuper junction silicon devices reduce theoutput capacitance by 20 % and the

reverse recovery charge Qrr of the intrinsicbody diode by 25 %, that is a far distancebehind the effective Qrr of the new GaNtransistors which reduce Qrr by 95 %.While GaN was behind SiC for powerdevices, its pace of progress has beenrapid, overtaking that of SiC in manyapplications and thereby capturing theinterest of systems manufacturers.

Rejecting some of the mythsWhen discussing the latest trends in HVGaN products is best to begin by rejectingsome of the myths. First, dynamic on-resistance or current collapse has beeneliminated for 600 V products back in2009. Second there were many peoplewho believed that it was not possible tomake and qualify 600 V GaN on Silicon.With the recent JEDEC qualification ofTransphorm’s first generation of GaN-on-Sidevices, we believe that has also been laid

to rest as well as the issue that dislocationswould prevent such an accomplishment.The initial 600 V products include both

diodes and GaN high electron mobilitytransistors (HEMT). The TPH3006PSHEMT combines low switching andconduction losses to reduce energy loss by50 percent compared to conventionalSilicon-based power conversion designs.The TO-220-packaged GaN transistorfeatures low on-state resistance of 150m�, low reverse-recovery charge of 54 nCand thus high-frequency switchingcapability. As illustrated in Figure 1, theHEMT is capable of switching 400 V in 3.5ns. It is this fast switching that makes thehigher performance achievable. While fastswitching is expected with GaN devices,the low capacitance of the GaN HEMTimproves the performance in resonantswitching more than expected.Also available in industry-standard TO-

Figure 1: Switching characteristicsof the TPH3006PS HEMT

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www.power-mag.com Issue 5 2013 Power Electronics Europe

220 packages, the TPS3410PK andTPS3411PK GaN diodes offer 6 A and 4 Aoperating currents, respectively, with aforward voltage of 1.3 V. In addition, threeapplication kits — PFC (TDPS400E1A7),Daughter Board (TDPS500E0A) and MotorDrive (TDMC4000E0I) — are available forrapidly benchmarking the in-circuitperformance.

High-efficiency applicationsWith the implementation of a highefficiency off-line 1 kW 48 V power supplya peak efficiency of 97.5 percent has been

demonstrated . The power supply designutilizes a 99 % efficient totem pole powerfactor correction (PFC) front end,combined with a 98.6 % efficiency LLCconverter (Figure 2). A prototype circuithas been displayed at the PCIM EuropeConference and Exhibition.

ConclusionGaN devices for high voltage have nowmoved out of the lab and into systemsproviding designers new tools with whichto continue enabling greater systemsperformance. The completion of

qualification of GaN at 600 volts clearlydispels several myths that were previouslyrepeated in order to predict a very limitedopportunity for GaN.

Literature“Latest High Voltage GaN Devices for

Inverters”, PEE Special Session PowerGaN for Highly Efficient Converters,PCIM Europe 2013, Nuremberg

Figure 2: Off-line 1kW 48 V powersupply reaches apeak efficiency of97.5 percent utilizingGaN devices

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