Study on Characteristics of Enhancement-Mode Gallium-Nitride High-Electron-Mobility Transistor for the Design of Gate Drivers

Transcription

1 electronics Article Study on Characteristics of Enhancement-Mode Gallium-Nitride High-Electron-Mobility Transistor for Design of Gate Drivers Sheng-Yi Tang Department of Power Mechanical Engineering, National Formosa University, Yunlin County 6321, Taiwan; Tel.: Received: 1 September 22; Accepted: 21 September 22; Published: 25 September 22 Abstract: An enhancement-mode gallium-nitride high-electron-mobility transistor (E-mode GaN HEMT) operated at high frequency is highly prone to current spikes (di/dt) and voltage spikes (dv/dt) in parasitic inductor of its circuit, resulting in damage to power switch. To highlight phenomena of di/dt and dv/dt, this study connected drain, source, and gate s in series with inductors (L D, L S, and L G, respectively). The objective to explore effects of di/dt and dv/dt phenomena and operating frequency (f S ) on drain-to-source voltage (V ds ), drain-to-source current (I ds ), and gate-to-source voltage (V gs ). The experimental method comprised two projects: (1) establishment of a measurement system to assess change of electrical characteristics of E-mode GaN HEMT and (2) change of f S and inductances (i.e., L D, L S, and L G ) in circuit to measure changes in V ds, I ds, and V gs, thus summarizing experimental results. According to experimental results on electrical characteristics, a gate driver circuit may be designed to drive and protect E-mode GaN HEMT while being actually applied to a 12-W synchronous buck converter with an output voltage of 12 V and an output current of A. Keywords: enhancement-mode gallium-nitride high-electron-mobility transistor; gate driver; synchronous buck converter 1. Introduction The gradual yearly increase of greenhouse gases has intensified global warming. Energy-saving and carbon reduction have become primary development goals for each country. The demand for relevant regulations (e.g., Energy Star Standard and California Energy Commission Appliance Efficiency Regulations) and market in recent years have driven continual development of high-efficiency and high-power-intensity power supply units [1,2]. Because wide-bandgap materials are characterized by high breakdown voltage and high electron mobility, which merit operation under high temperatures and high frequencies [3 ], y have enabled development of power supply units to gradually transition from silicon power switches to wide-bandgap power switches [3 5]. Wide-bandgap semiconductors may be categorized by ir internal structures into enhancement-mode gallium-nitride high-electron-mobility transistors (E-mode GaN HEMTs) and gallium-nitride high-electron-mobility transistors (GaN HEMTs) [11]. Table 1 presents a comparison between key parameters (static, dynamic, and reverse operation) of E-mode GaN HEMT and GaN HEMT. The following findings were revealed from comparison: (1) regarding static parameters, E-mode GaN HEMT with a R DS(ON) value smaller than that of GaN HEMT yielded lower conduction loss. (2) Regarding dynamic parameters, both transistors are voltage-driven components that require charging and discharging of a parasitic inductor between gate-to-source and gate-to-drain s for conduction and cut-off. That is, because total gate charge (Q G ), gate source charge (Q GS ), Electronics 22, 9, 1573; doi:.339/electronics

2 Electronics 22, 9, of 11 and gate drain charge (Q GD ) of E-mode GaN HEMT were lower than those of GaN HEMT, E-mode GaN HEMT required less time for conduction and cut-off as well as experienced weaker di/dt and dv/dt. (3) Reverse-recovery charge (Q RR ) of E-mode GaN HEMT approximately zero under reverse operation, constituting an extremely short reverse recovery time as well as minimal component loss and electromagnetic interference. Given three aforementioned advantages of E-mode GaN HEMT, this study employed it for experiment. Table 1. The key parameters compare enhancement-mode gallium-nitride high-electron-mobility transistors (E-mode GaN HEMTs) with GaN HEMT [12,13]. Key Parameter E-Mode GaN HEMT GaN HEMT Unit Static Dynamic R DS(ON) (15 C) 37 5 mω Q G nc Q GS 1.4 nc Q GD nc Reverse Operation Q RR 136 nc High-frequency operation subjects parasitic inductor of circuit to di/dt and dv/dt phenomena, which could entail oscillation in voltage and current waveforms and create electromagnetic interference. Serious electromagnetic interference can result in damage to power switch [14]. A measurement system first established to assess electrical characteristics of E-mode GaN HEMT. Subsequently, to accentuate di/dt and dv/dt phenomena, this study connected drain, source, and gate s in series with inductors (L D, L S, and L G, respectively) and adjusted inductor values before measuring waveform changes of V ds, I ds, and V gs. In addition, this study adjusted operating frequency from khz to 2 MHz to measure waveform changes of V ds and V gs. Based on results from electrical characteristic experiment, this study s aim to design a gate driver circuit to drive E-mode GaN HEMT while furr protecting said transistor by monitoring changes in V gs and I ds values. In Sections 2 and 3, measurement system and electrical characteristics of E-mode GaN HEMT are introduced, respectively. Section 4 details circuit framework and application of gate driver circuit, whereas Section 5 presents conclusion. 2. Measuring System When E-mode GaN HEMT is switched on or off, di/dt and dv/dt phenomena occur. Therefore, at various operating frequencies, load currents, and inductances, a measurement system used to assess and record changes in V ds, I ds, and V gs. Figure 1 presents measurement system, composed of a function generator (fabricant: SIGLENT, model: SDG242X), a passive circuit, a digital oscilloscope (fabricant: LECROY, model: HDO434A), a DC power supply (fabricant: GWINSTEK, model: SPD-366), and an E-mode GaN HEMT ( testing component; fabricant: GaN system, model:gs64b). The experimental parameters in Figure 1 are detailed in Table 2.

3 Electronics 22, 9, of 11 Electronics 22, 9, x FOR PEER REVIEW 3 of 11 R dc Passive Circuit Q 1 C GD D L D L G Function generator f s R G_ON R G_OFF D 1 D 2 v gs G C GS S C GS DC power supply V dc PWM Digital oscilloscope v gs i ds L S i ds Figure 1. The proposed measurement system to assess electrical characteristics of enhancement-mode gallium-nitride high-electron-mobility transistors (E-mode GaN HEMT). Table 2. Experimental parameters of Figure 1. Table 2. Experimental parameters of Figure 1. Symbol Value Unit Symbol Value Unit V dc 12 V I dc Vdc V A f s 2 khz L D Idc A µh L S.1 3. µh fs L 2 khz G.1 3. µh R G_ON 2 Ω LD.1 3. μh R G_OFF Ω D 1 and DLS 2 1N μh - 1N4148 specification [15] LG.1 3. μh Fabricant Diodes - Non-Repetitive Peak Reverse RG_ON Voltage (V RM ) 2 Ω V Forward Continuous Current (I FM ) 3 ma Reverse Recovery RG_OFF Time (t RR ) 4 Ω ns V ds,max of GS64B V D1 and D2 1N I ds,max of GS64B 3 A V gs,max of GS64B 1N4148 specification [15] 7 V 3. Electrical Characteristics of E-mode Fabricant GaN HEMT when di/dt and Diodes dv/dt Occur - Regarding Figure Non-Repetitive 2, GS64B Peak component Reverse Voltage provided (VRM) by GaN Systems V loaded into TINA-TI; after a circuit diagram Forward (Figure 2) Continuous plotted, Current V(IFM) ds, I ds, and V gs 3 waveforms ma can be simulated. The simulation performed in condition of I ds = 2 A and f s = 15 khz with inductance parameters of L Reverse Recovery Time (trr) 4 ns G = nh, L D = 5 nh, and L S = 5 nh. The obtained waveforms of I D (I ds ), V ds, and V gs from simulation are Vds,max presented of GS64B in Figure 3. To elucidate exact V time when di/dt and dv/dt occurred in waveform, maximum and minimum values of I ds were marked as I ds,max Ids,max of GS64B 3 A and I ds,min, respectively; maximum and minimum values of V ds were denoted by V ds,max and V ds,min, respectively; and maximum Vgs,max of GS64B and minimum values of V7 gs were marked V as V gs,max and V gs,min, respectively. Subsequent experiments were implemented and recorded according to 3. aforementioned Electrical Characteristics rules. of E-mode GaN HEMT when di/dt and dv/dt Occur Regarding Figure 2, GS64B component provided by GaN Systems loaded into TINA- TI; after a circuit diagram (Figure 2) plotted, Vds, Ids, and Vgs waveforms can be simulated. The

4 of LG = nh, LD = 5 nh, and LS = 5 nh. The obtained waveforms of ID(Ids), Vds, and Vgs experiments were implemented and recorded according to aforementioned rules. from simulation are presented in Figure 3. To elucidate exact time when di/dt and dv/dt occurred in waveform, maximum and minimum values of Ids were marked as Ids,max and Ids,min, respectively; maximum and minimum values of Vds were denoted by Vds,max and Vds,min, respectively; and maximum and minimum values of Vgs were marked as Vgs,max and Vgs,min, respectively. Subsequent Electronics 22, 9, of 11 experiments were implemented and recorded according to aforementioned rules. The parameters presented in Figure 2, namely output current, operating frequency (fs), and inductors in series (i.e., LD, LS, and LG), were changed. In four testing conditions, maximum and minimum values of Vds, Ids, and Vgs were measured and recorded to determine spike changes. Figure 2. Circuit simulation in TINA-TI. Figure 2. Circuit simulation in TINA-TI. The parameters 3. presented I ds,max in Figure 2, namely output current, operating frequency (fs), and inductors in series (i.e., LD, LS, and LG), were changed. In four testing conditions, maximum and minimum values of Vds, Ids, and Vgs were measured and recorded to determine spike changes I ds,max V ds,max Figure 2. Circuit simulation in TINA-TI. I ds,min I ds,min V ds,min V gs,max V ds,max V ds,min V gs,max V gs,min μ 2 μ 3 μ 4 μ 5 μ Time (s) Figure Simulation of of waveform changes in in I ds Ids,, VVds,, and VVgs when di/dt and dv/dt occur. V gs,min Applying The parameters Various LD presented Values to Measure in Figure 2, Changes namely in Ids output and Vds current, when di/dt operating and dv/dt frequency Occur (f μ 2 μ 3 μ 4 μ 5 μ s ), and inductors in series (i.e., L The parameter setting of D, L LG = S, and L LS = 1 nh, G ), were changed. In four testing conditions, maximum fs = Time khz, (s) Vgs = 5 V, and LD =.1.5 μh applied. and minimum values of V Figure 4a shows that under ds, I different ds, and V gs were measured and recorded to determine spike changes. Ids (ranging from.1 A to 2. A) and before LD achieved.1 μh, Figure 3. Simulation of waveform changes in Ids, Vds, and Vgs when di/dt and dv/dt occur. Vds,max changes of five curves exhibited a linear relationship. After LD exceeded.1 μh, Vds,max 3.1. Applying Various L D Values to Measure Changes in I ds and V ds when di/dt and dv/dt Occur 3.1. underwent Applying a Various rapid change, LD Values where to Measure Vds,max Changes value of in Ids and blue and Vds when yellow di/dt and curves dv/dt approximated Occur specification The parameter of GS64B setting of L (Vds,max G = L S = V); 1 nh, at fthat s = point, khz, V gs experiment = 5 V, and L D = terminated.1.5 µh to avoid applied. The Figure parameter 4a shows setting that of LG under = LS = different 1 nh, fs = I ds (ranging khz, Vgs from = 5 V,.1and A told 2. =.1.5 A) before μh L D achieved applied. Figure.1 µh, 4a shows V ds,max that changes under of different five Ids curves (ranging exhibited from a.1 linear A to relationship. 2. A) and before After LD L D achieved exceeded.1 μh, µh, V ds,max Vds,max underwent changes aof rapid five change, curves where exhibited V ds,max a linear value relationship. of blue After and yellow LD exceeded curves approximated.1 μh, Vds,max underwent specification a rapid of GS64B change, where (V ds,max = Vds,max V); value at that of point, blue and experiment yellow curves terminated approximated to avoid specification damaging of power GS64B switch. (Vds,max As= presented V); at inthat Figure point, 2, because experiment drain- and terminated source-end to of avoid GS64B exhibited parasitic capacitance (C ds ), an RLC series network formed with loops of V dc, R dc, L D, C ds, and L S. Therefore, with circuit parameters R dc = 6 Ω, L S = 1 nh, L D =.5.3 µh, and C ds = 5 pf [16], damping ratio (ζ) [17] calculated to be.137,.125,.116,.9,.2,.97,.69, and.56. The curve of I ds = 2 A in Figure 4a illustrates relationship between L D and V ds,max. When ζ =.137 (L D =.5 µh), V ds,max amplitude low, whereas it high when ζ =.56 (L D =.3 µh).

5 to 3. μh and Points a, b, and c correspond to points a, b, and c in Figure 4a. The researcher continued to increase LD until gray curve first yielded Vds,max = 98 V; experiment for gray curve terminated. Subsequently, when LD increased to 3. μh, orange and light blue curves yielded Vds,max values of V and V, respectively, both of which are lower than Vds,max = V. Electronics 22, 9, of 11 Vds,max (V) Ids.1 A 9 Ids.5 A 8 Ids 1. A 7 Ids 1.5 A Ids 2. A Ids 2. A Ids 1.5 A Ids 1. A Ids.5 A Ids.1 A.5..5 LD (μh) (a) c b a V ds,max (V) 9 8 I ds 1. A I ds.5 A 7 c 6 Ids.1 A b Ids.5 A Ids 1. A 2 a I ds.1 A L D (μh) (b) Figure4. 4. Changes in Vds V Ids Vds,max for Ids ds when different I ds values are applied. (a) Changes in V ds,max for various I ds values (LD from μh). (b) in Vds,max for various Ids values (LD D ranges from.1.5 µh). (b) Changes in V ds,max for various I ds values ranges (L D ranges from from μh). µh) Applying Subsequently, Different LG VValues ds,max values to Measure of corresponding Changes of Points Vds and a Vgs (12.1 When V), di/dt b (26.26 and dv/dt V), and Occur c (6.49 V) on gray, orange, and light blue curves, respectively, were found to not reach V. Therefore, The parameter setting of Ids = 2 A, LS = 1 nh, fs = khz, Vgs = 5 V, and LG =.1.5 μh researcher could continue to increase L applied. In Figure 5a, orange (Vds,min,a) and gray D for three curves. In Figure 4b, L curves (Vds,max,a) are used for when D ranges from LD =.2 μh and.5 µh to 3. µh and Points a blue (Vds,min,b) and yellow curves, b (Vds,max,b), and c for correspond to points a, b, and c in Figure 4a. The researcher LD = 1. nh to observe Vds changes. A comparison of Vds,min,a continued to increase L and Vds,min,b values when D until gray curve first yielded V LG changed from.1 μh to ds,max = 98 V; experiment for gray.5 μh revealed that Vds,min,b still curve terminated. Subsequently, when L approximately zero, whereas Vds,min,a ranged from 1.33 D increased to 3. µh, orange and light V to 1.4 V. Because drain of blue curves yielded V GS64B connected ds,max values of V and V, respectively, both of which are lower than to LD = 1 nh, inductance relatively low, with Vds,max,b remaining at V approximately ds,max = V. 12 V; almost no change observed. By contrast, when LD =.2 μh, inductance increased, with Vds,max,a 3.2. Applying Different ranging L between 72 V and 76 V. This shows that connecting drain G Values to Measure Changes of V ds and V gs When di/dt and dv/dt Occur of GS64B to an inductor with excessively large inductance causes an increase in Vds,max and Vds,min. The The blue parameter (Vgs,min,a) setting and red of I curves ds = 2 A, (Vgs,max,a) L S = 1 are nh, used f s = for when khz, V LD gs =.2 5 V, μh, and and L G =.1.5 gray (Vds,min,b) µh and yellow applied. curves In Figure (Vds,max,b) 5a, orange are used (V when ds,min,a ) and LD = 1. gray nh curves to observe (V ds,max,a changes ) are used of Vgs, for as when shown L D in = Figure.2 µh 5b. and Before blue (V LG ds,min,b reached ) and.1 yellow μh, curves Vgs,min,a ranged (V ds,max,b from ) for.34 L D = 1. V to nh.49 to observe V, but rose V ds changes. to A comparison V after of LG reached V ds,min,a.1 and μh. V ds,min,b values Vgs,min,b remained when almost L G changed before from LG reached.1.2 µh μh, to.5 but µh revealed range of that V Vgs,min,b ds,min,b rose to.73.8 still approximately V after LG reached zero, whereas.2 μh. V ds,min,a When ranged LD from set to μh, V to 1.4 Vgs,max,a ranged V. Because from 5. drain V to 6.85 V; when of GS64B LD set to 1. nh, connected Vds,max,b ranged to L D = from 1 nh, 5. V inductance to 6.97 V. Neir relatively voltage low, value with exceeded V ds,max,b remaining specifications at approximately for GS64B 12 V; almost (Vgs,max = 7 V). no Because change drain observed. By of contrast, GS64B when L D connected =.2 µh, to LD, inductance no direct effect increased, exerted with V ds,max,a on ranging Vgs,max and Vgs,min. between The 72 gate V and 76 V. of This GS64B shows that connecting connected to LG, drain which caused of GS64B Vgs,max and to an Vgs,min to inductor increase with with excessively value of large LG. inductance causes an increase in V ds,max and V ds,min. The blue (V gs,min,a ) and red curves (V gs,max,a ) are used for when L D =.2 µh, and gray (V ds,min,b ) and yellow curves (V ds,max,b ) are used when L D = 1. nh to observe changes of V gs, as shown in Figure 5b. Before L G reached.1 µh, V gs,min,a ranged from.34 V to.49 V, but rose to V after L G reached.1 µh. V gs,min,b remained almost before L G reached.2 µh, but range of V gs,min,b rose to.73.8 V after L G reached.2 µh. When L D set to.2 µh, V gs,max,a ranged from 5. V to 6.85 V; when L D set to 1. nh, V ds,max,b ranged from 5. V to 6.97 V. Neir voltage value exceeded specifications for GS64B (V gs,max = 7 V). Because drain of GS64B connected to L D, no direct effect exerted on V gs,max and V gs,min. The gate of GS64B connected to L G, which caused V gs,max and V gs,min to increase with value of L G.

6 Electronics 22, 9, of 11 Electronics 22, 9, x FOR PEER REVIEW 6 of 11 V ds (V) V ds,min,a V ds,max,a V ds,min,b V ds,max,b L G (μh) (a) 8 V gs (V) V gs,min,a 3 V gs,max,a 2 V gs,min,b 1 V gs,max,b L G (μh) (b) Figure 5. Changes in VVds Vgs LG Vds,max and Vds,min ds and V gs for different L G values. (a) Changes in V ds,max and V ds,min for for different different LLG in Vgs,max and Vgs,min for different LG G values. (b) Changes in V gs,max and V gs,min for differentvalues. L G values Applying Different LS L S Valuesto to Measure Changesof ofids, I ds Vds,, V ds and, and Vgs VWhen gs When di/dt di/dt and and dv/dt dv/dt Occur Occur The parameter setting ofids I ds = = 2 A, 2 A, LG L= G 1 = nh, 1 nh, fs = f s = khz, khz, Vgs = V5 gs V, = and 5 V, LS and =.1 2. L S =.1 2. μh µh applied. applied. The blue The curve blue curve (Ids,min,a) ds,min,a is used ) is when usedld when =.2 μh L D and =.2 µhorange and curve orange (Ids,min,b) curve is used (I ds,min,b when ) is used LD = 1. when nh to L D observe = 1. nh changes to observe of Ids. In changes Figure 6a, of Ids,min,a. Inranges Figurefrom 6a, 1.4 I ds,min,a A to ranges 1.84 from A, whereas 1.4 A to 1.84 changes A, of whereas Ids,min,b are divided changesinto of I ds,min,b three sections are divided detailed into as three follows. sections In detailed first section, as follows. where InLS first ranged section, from where.1 to L S. ranged μh, from Ids,min,b.1 approximately to. µh, I ds,min,b A; in approximately second section, where A; inls ranged second section, from.1 where μh to L.1 S ranged μh, Ids,min,b from.1 between µh to.11 A µh, and I ds,min,b 1.13 A; and between in third.11 section, A andwhere 1.13LS A; and ranged in from third.1 μh section, to 2. μh, where Ids,min,b L S ranged between from µh A and to µh, A. As I ds,min,b shown in between Figure 6a, 1.13 when A and Ls = μh A. and As1. shown μh, in Ids,min Figure decreased 6a, when sharply. L s = Theses.1 µh phenomena and 1. are µh, elucidated I ds,min decreased follows: sharply. As Theses indicated phenomena by blue are curve, elucidated in Ids as loop, follows: inductance As indicated value for by series blueconnection curve, in of LD I ds =.2 loop, μh inductance and LS =.1 value μh for LDS(blue) series= connection.21 μh, and of LIds,min D =.2 = 1.4 µha; and when L S = LD.1 =.2 µhμh and L DS(blue) LS = 1. =.21 μh, µh, and LDS(blue) I = 1.2 μh and Ids,min ds,min = 1.4 A; when= L 1.69 D =.2 A. The µhinductance and L S = 1. increased µh, L DS(blue) by 5.7 times = 1.2 from µh and.21 IμH ds,min to = μh, A. The indicating inductance a significant increased change by 5.7in times Ids,min. from As depicted.21 µh to by 1.2 orange µh, indicating curve, a significant inductance change value in for I ds,min. As series depicted connection by of orange LD = 1 curve, nh (.1 inductance μh) and LS value =.1 for μh series LDS(orange) connection =.11 μh, of L and Ids,min D = 1 nh = (.1.1 A; µh) and when L LD = 1 nh (.1 μh) and LS 1. μh, LDS(orange) = 1.1 μh, and Ids,min S =.1 µh L DS(orange) =.11 µh, and I ds,min =.1 A; when L= D 1.7 = 1 A. nh The (.1 inductance µh) and increased 91 times from.11 μh to 1.1 μh, indicating that change in Ids,min L larger for S = 1. µh, L DS(orange) = 1.1 µh, and I ds,min = 1.7 A. The inductance increased 91 times from.11 orange µh tocurve 1.1 than µh, indicating for blue that curve. change in I ds,min larger for orange curve than for In Figure 6b, blue (Vds,min,a) and orange curves (Vds,max,a) are used when LD blue curve. =.2 μh and gray and yellow curves are used when LD = 1. nh to observe changes in Vds. In section where LS In Figure 6b, blue (V ds,min,a ) and orange curves (V ds,max,a ) are used when L D =.2 µh and between.1 μh and.1 μh, Vds,min,a ranged between 2.16 V and 2.49 V, whereas Vds,max,a gray and yellow curves are used when L D = 1. nh to observe changes in V ds. In section where L S ranged between V and V. After LS reached.1 μh, Vds,min,a between.1 µh and.1 µh, V did not exhibit much variation, ds,min,a ranged between 2.16 V and 2.49 V, whereas V ds,max,a but Vds,max,a rose considerably to V. The value of Vds,min,b approximated until LS ranged between V and V. After L reached S reached.1 µh, V ds,min,a did not exhibit much variation,.1 μh, which when Vds,min,b decreased from to 2.5 V. Changes in Vds,max,b may be divided into but V ds,max,a rose considerably to V. The value of V ds,min,b approximated until L S reached three sections: When LS =.1. μh,.1. μh, and.1.3 μh, corresponding ranges of.1 µh, which when V ds,min,b decreased from to 2.5 V. Changes in V ds,max,b may be divided into Vds,max,b were V, V, and V, respectively. Because in third section, three sections: When L S =.1. µh,.1. µh, and.1.3 µh, corresponding ranges Vds,max,b approximating V, subsequent experiment terminated. According to of V ds,max,b were V, V, and V, respectively. Because in third aforementioned experimental results, reducing LD to 1 nh, maintaining LS in loop of Ids, gradually section, V ds,max,b approximating V, subsequent experiment terminated. According to increasing LS caused Ids,max, Ids,min, Vds,max, and Vds,min to rise. aforementioned experimental results, reducing L In Figure 6c, blue curve (Vgs,min,a) is used when D to 1 nh, maintaining L LD =.2 μh, and orange S in loop of I curve (Vgs,min,b) is ds, gradually increasing L used when LD = 1. nh S caused I to observe ds,max, I changes ds,min, V of Vgs. ds,max, and V Vgs,min,a began ds,min to rise. at.4 V and continued to drop until LS reached.2 μh, after which it gradually stabilized and eventually remained at approximately.7 V. The variation in Vgs,min,b may be divided into two sections. When LS =.1.1 μh, Vgs,min,b.12 V, showing negligible variation. When LS =.2 2. μh, Vgs,min,b.73.4 V. This experiment revealed that because LS not in loop of Vgs, its effect on Vgs,min limited.

7 Electronics 22, 9, 1573 x FOR PEER REVIEW 7 of 11.5 I ds,min (A) I ds,min,a I ds,min,b L S (μh) (a) V ds (V) V ds,min,a 3 V 2 ds,max,a V ds,min,b V ds,max,b L S (μh) (b) V gs (V) V gs,min,a -.6 V gs,min,b L S (μh) (c) Figure 6. Changes in IIds, Vds, Vgs LS Ids, V ds, and V gs when different L S are applied. (a) Changes in I ds for different LS. L S. (b) Changes in Vds ds for different LS. L S.(c) Changesin invgs V gs for for differentls. L S Applying In FigureDifferent 6c, blue LS Values curve to (VMeasure gs,min,a ) is used Changes whenof L D Ids, = Vds,.2 and µh, Vgs andwhen orange di/dt and curve dv/dt (VOccur gs,min,b ) is used when L D = 1. nh to observe changes of V gs. V gs,min,a began at.4 V and continued to drop The parameter setting of Ids = 1 A, LG = nh, LD = LS = 1 nh, Vgs = 5 V, and fs = khz 2 MHz until L S reached.2 µh, after which it gradually stabilized and eventually remained at approximately.7 applied. V. The variation In Figure 7, in V gs,min,b blue (Vds,max), may be orange divided (Vgs,min), intoand twogray sections. (Vgs,max) When curves Lare S = used.1.1 to observe µh, Vchanges gs,min,b in both.12 Vds and V, showing Vgs,. Vds,max negligible found variation. to remain Whenat L S approximately =.2 2. µh, V15 gs,min,b V, Vgs,min.73.4 remained at V. This approximately experiment.64 revealed V, and that Vgs,max because varied L S from 5.61 not in V to 6.12 loopv. of According V gs, its effect to onexperimental V gs,min limited. results, parasitic capacitance of E-mode GaN HEMT extremely low. Take GS64B as an example, 3.4. Applying Different L S Values to Measure Changes of I ds, V ds, and V gs When di/dt and dv/dt Occur Ciss = 328 pf, Coss = 133 pf, and CRss = 5 pf. This shows that operating frequency of khz 2 MHz The parameter setting of I ds = 1 A, L G = nh, L D = L S = 1 nh, V gs = 5 V, and f s = khz 2 MHz suitable for GS64B. applied. In Figure 7, blue (V ds,max ), orange (V gs,min ), and gray (V gs,max ) curves are used to observe changes in both V ds and V V gs,. V ds,max found to remain at approximately 15 V, V gs,min remained at approximately.64 16V, and V gs,max varied from 5.61 V to 6.12 V. According to experimental results, parasitic capacitance 14 of E-mode GaN HEMT extremely low. Take GS64B as an example, C iss = 328 pf, C oss = pf, and C Rss = 5 pf. This shows that operating frequency of khz 2 MHz suitable for GS64B V ds,max V gs,min V gs,max f S (khz)

8 changes in both Vds and Vgs,. Vds,max found to remain at approximately 15 V, Vgs,min remained at approximately.64 V, and Vgs,max varied from 5.61 V to 6.12 V. According to experimental results, parasitic capacitance of E-mode GaN HEMT extremely low. Take GS64B as an example, Ciss = 328 pf, Coss = 133 pf, and CRss = 5 pf. This shows that operating frequency of khz 2 MHz Electronics 22, 9, of 11 suitable for GS64B V 4. V ds,max 2. V gs,min V gs,max -2. Electronics 22, 9, x FOR PEER REVIEW of 11 f S (khz) Figure 7. Changes in Vds and Vgs when different fs values are applied. Figure 7. Changes in V ds and V gs when different f s values are applied Framework and Application of of Gate Driver Circuit According to to aforementioned experimental results, connecting inductors with excessively large inductance in in series series to to circuit circuit loop loop of Vof Vgs gs and and I Ids ds tends tends to to aggravate dv/dt dv/dt and and di/dt di/dt phenomena. To To avoid drastic spikes in in voltage and and current waveforms that that may damage E-mode GaN HEMT, this this study study designed designed a gate a gate driver driver circuit circuit in in hope hope of protecting of protecting E-mode E-mode GaN GaN HEMT HEMT by monitoring by monitoring V Vgs gs and and I Ids ds values. values. In In Figure Figure 8, 8, gate gate driver driver circuit comprises aa controller, an an isolated driver (UCC2152), a gate driver (LM5113), a high-speed amplifier (AD828), and a shunt resistor (R(RS). S When pulse width modulation (PWM) signal of of VVgs is switched from on to off, controller detects positive and and negative trigger sources to to ensure ensure that that VVgs does not exceed range between V and and 4 4 V. V. When When E-mode GaN GaN HEMT is is switched on on or or off, off, controller detects detects I Ids ds changes through shunt resistor to to ensure that that IIds remains within designated value range. When Vgs V gs or orids I ds exceeds exceeds set set range, range, controller turns turnsoff off gate driver to avoid damage to E-mode GaN GaN HEMT. In In addition, gate gate driving circuit is is composed of of three s: A, A, B, B, and C. C. Terminal A is is connected to to gate gate of of E-mode GaN HEMT, Terminal B is is connected to to source of of E-mode GaN GaN HEMT, and and Terminal CC is is connected to to or or components (Figure (Figure 9). 9). Gate driver for E-mode GaN Detecting OVP, UVP and rising/falling edge for V gs AD828 Drain Controller PWM _GaN UCC2152 Detecting OCP and rising/falling edge for I ds LM5113 AD828 A Gate v gs1_gan + - V BC E-mode GaN Source B Rs C Figure Block diagram of of gate driver circuit. Q H L 1 Vin E-mode GaN HEMT PWM H PWM Gate driver H E-mode GaN HENT PWM L Gate driver L Q L Z D C o + V o Load

9 v gs1_gan Source Detecting OCP and B rising/falling edge for I ds + AD828 V BC Rs - C Electronics 22, 9, of 11 Figure 8. Block diagram of gate driver circuit. Q H L 1 Vin E-mode GaN HEMT PWM H PWM Gate driver H E-mode GaN HENT PWM L Gate driver L Q L Z D C o + V o Load Figure Figure Application of of gate driver circuitto to synchronousbuck buckconverter. converter. In In Figure 9, 9, two two gate driver circuits are installed to synchronous buck converter, which whichis is applied applied to to a a 48-V 48-V electric scooter system. Parameters appliedto to synchronousbuck buck converter are are presented in Table 3. Figure a shows QH and QL presented in Table 3. Figure a shows PWM waveforms of Q subject to no-load current; H and Q L subject to no-load current; green green waveform waveform shows thatat ata a.18.18duty duty cycle, cycle, dv/dt dv/dt at at negative negative 1.6 V. 1.6 The V. The red red waveform waveform indicates indicates that, that, at a.77 at a duty.77 cycle, duty cycle, spike dv/dt spike at dv/dt negative at negative 1.9 V. Figure b shows PWM waveforms of QH and QL subject to a full-load current. The green 1.9 V. Figure b shows PWM waveforms of Q H and Q L subject to a full-load current. The green waveform shows that at a.28 duty cycle, dv/dt at negative 1.6 V. The red waveform shows that at a.28 duty cycle, dv/dt at negative 1.6 V. The red waveform indicates that, at a.7 duty cycle, dv/dt at negative 3.6 V. Waveforms waveform indicates that, at a.7 duty cycle, dv/dt at negative 3.6 V. Waveforms of output voltage (V o ) and output current (I o ) of synchronous buck converter are presented in Figure 11, where V o = 12.2 V and I o =. A, both of which meet specifications in Table 3. Table 3. Experimental parameters of Figure 9. Symbol Value Unit V in(min) 36.8 V V in(max) 57.6 V P o 12 W V o 12 V I o A V o /V o 1 % Electronics 22, 9, x FOR PEER REVIEW I o /I o % 9 of 11 f s 8 khz of output voltage (Vo) and output Duty current ratio(io) of.18synchronous - buck converter are presented in Figure 11, where L µh Vo = 12.2 V and Io =. A, both of which meet specifications in Table 3. C o 38 µf High side E-mode GaN HEMT Duty Ratio=.18 High side E-mode GaN HEMT Duty Ratio=.28 Low side E-mode GaN HEMT Duty Ratio=.77 Low side E-mode GaN HEMT Duty Ratio=.7 (a) (b) Figure.. PWM signalsof of E-modeGaN GaNHEMT. (a) (a) No-load, No-load, 2 V/div, 2 V/div, time: time: 1 μs/div. 1 µs/div. (b) Full-load, (b) Full-load, 2 2 V/div, time: 11 μs/div. µs/div. V o = 12.2 V

10 (a) (b) Electronics Figure 22,. 9, PWM 1573 signals of E-mode GaN HEMT. (a) No-load, 2 V/div, time: 1 μs/div. (b) Full-load, 2 of 11 V/div, time: 1 μs/div. V o = 12.2 V I o = A Figure Figure Waveforms of of output output voltage voltage and and output output current. current. 5 5 V/div, 55 A/div, time: ms/div. 5. Conclusions Table 3. Experimental parameters of Figure 9. This study explored factors influencing spike magnitude when di/dt and dv/dt occur to GS64B. A gate drive circuit designedsymbol and applied to Value synchronous Unit buck converter. The following conclusions were drawn from experimental results. Vin(min) 36.8 V 1. When dv/dt of V ds and di/dt Vin(max) of I ds are excessively 57.6 large, V L D of I ds circuit loop may first be reduced before L S is reduced. Po 12 W 2. When dv/dt of V gs is excessively large, L G of V gs circuit loop may first be reduced. Vo 3. When L 12 V D, L G, and L S are maintained at a minimum value, optimal operating frequency for GS64B is khz 2 MHz. Io A 4. The gate driver circuit is suitable for 12-W synchronous buck converter. ΔVo/Vo 1 % ΔIo/Io % Funding: This research funded by Ministry of Science and Technology as a Project of MOST Research (No. MOST E-15-4-MY2). fs 8 khz Conflicts of Interest: The authors declare Duty noratio conflict of interest References L1 2.7 μh 1. Radić, A.; Ahssanuzzaman, S.M.; Mahdavikhah, B.; Prodić, A. High-Power Density Hybrid Converter Topologies for Low-Power DC-DC SMPS. In Proceedings of 214 International Power Electronics Conference (IPEC-Hiroshima 214-ECCE ASIA), Hiroshima, Japan, May 214; pp Halder, T. Power Density & Thermal Limits of Flyback SMPS, Flyback SMPS. In Proceedings of 216 IEEE First International Conference on Control, Measurement and Instrumentation (CMI), Kolkata, India, 8 January 216; pp Avila, A.; Garcia-Bediaga, A.; Oñederra, O.; Ruias, A.; Rodriguez, A. Comparative Analysis of GaN HEMT vs. Si Cool MOS for a High-Frequency MMC Topology. In Proceedings of th European Conference on Power Electronics and Applications (EPE 17 ECCE Europe), Warsaw, Poland, September 217; pp Balda, J.C.; Mantooth, A. Power-semiconductor devices and components for new power converter developments. IEEE Power Electron. Mag. 216, 3, [CrossRef] 5. Millan, J.; Godignon, P.; Perpina, X.; Perez-Tomas, A.; Rebollo, J. A survey of wide bandgap power semiconductor devices. IEEE Trans. Power Electron. 214, 29, [CrossRef] 6. Ramachandran, R.; Nymand, M. Experimental demonstration of a 98.8% efficient isolated DC-DC GaN converter. IEEE Trans. Ind. Electron. 217, 64,

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