The Analysis and Research of the Integrated, 30 A MOSFET Gate Driver Dedicated to High-Frequency Applications

Abstract

This paper presents basic properties and laboratory tests of a commercial integrated high-frequency MOSFET gate driver IXRFD631 operating in the frequency range up to 30 MHz. The MOSFET driver has been tested for two operating states: in the idle state (no load) and at the gate load of a DE275-501N16A series MOSFET transistors. The obtained laboratory results were compared with three other commercial integrated drivers: DEIC420, DEIC515 and IXRFD630 (which are the base structures), and two previous solutions from the author (4xUCC27516 and 8xUCC27526). Additionally, this paper presents the characteristics of power losses and efficiency, measurements of switching and propagation times of the tested gate drivers. Also, this paper presents the output voltage waveforms of the integrated driver IXRFD631 for two operating states. The integrated circuit IXRFD631 of the gate driver is characterized by an efficiency of up to 70% for the tested frequency range, the power losses for two operating states (at idle state—15 W, at gate MOSFET load—43 W) and switching times of 2 ns for an operating frequency of 30 MHz.

1. Introduction

The subject of this article concerns issues related to the broadly understood power electronics and industrial electronics. In particular, it is related to the analysis of the properties, implementation and laboratory tests of the gate drivers dedicated to cooperation with power MOSFET transistors operating at frequencies up to several dozen megahertz (MHz). The continuous development of industrial electronics and the constantly expanding range of electronic parts and components encourage individual manufacturers to improve and modernize existing power electronics systems, e.g., class D, DE, or E resonant inverters. The continuous increase in interest and demand for this type of inverter with megahertz operating frequencies and power of up to several hundred kilowatts is noticeable in many industries.

The indispensable and most important electronic element that accompanies the previously mentioned resonant inverters is the power MOSFET transistor. This semiconductor element must be characterized by a high operating frequency while maintaining its static and dynamic parameters. In the high-efficiency electrical energy conversion that takes place in high-performance inverters [1,2,3,4,5,6,7,8,9], switching the power MOSFET transistor with a suitable high frequency and efficiency becomes a major challenge for the gate driver designer. To properly drive the gate of a single MOSFET transistor operating in an inverter system, e.g., class E, a dedicated gate driver system can be used. The main tasks of the gate driver include ensuring appropriate voltage levels for turning the transistor on and off and effectively recharging the gate’s internal capacity in the shortest possible time. Such effective switching should translate into the highest possible efficiency of the gate driver itself and the lowest possible power losses [4,5,9,10,11,12,13,14,15].

The most important elements of the gate circuit that influence the power losses and control efficiency of the MOSFET transistor are the gate charge Q_G and the gate resistance R_G. These two parameters are the main factors that determine the cooperation of the MOSFET transistor with a dedicated gate driver. These parameters influence the dynamic properties of the transistor, and their knowledge is necessary in the design process of, for example, a discrete resonant driver (so-called soft-switching driver). The smaller the gate charge and resistance values, the easier it is to achieve shorter switching times of the MOSFET transistor and the easier it is to control [1,2,3,4,5,7,8,11]. Datasheets often provide characteristics that enable direct reading of the Q_G gate charge, but there is no information about the R_G gate resistance. To turn on the MOSFET transistor, it is necessary to provide an appropriate voltage V_GS between the gate and the source, usually greater than the threshold voltage V_th. Due to the parasitic inter-electrode capacitances, the switch-on process requires a specific electric charge Q_G to be supplied to the gate. The situation is similar in the process of turning off the transistor—the accumulated gate charge must be discharged. Such a transfer of the gate charge Q_G in the shortest possible time t_G requires a gate current flow, the average value of which is defined by the equation [1,2,3,4,5,16,17]:

$$I_{\mathrm{G}}={\displaystyle \frac{Q_{\mathrm{G}}}{t_{\mathrm{G}}}}.$$

(1)

At the same time, during normal operation of the transistor, when it is cyclically switched, there is power loss in the gate circuit P_Q. The total power loss in the gate circuit of the transistor can be calculated from the following equation [1,2,3,4,5,11,16,17]:

$$P_{\mathrm{Q}}=V_{\mathrm{G}\mathrm{S}}·f·Q_{\mathrm{G}}.$$

(2)

As it results from the relation (2), the total power loss P_Q in the gate circuit of the transistor depends on the applied voltage V_GS, the gate charge Q_G of the transistor and the frequency f of the control signal (switching frequency). In the reviewed work (in Chapter 2), it was shown that with the increase in the transistor switching frequency, the average value of the gate current I_G increases, and thus the value of the power losses in the gate circuit increases.

Very often, in design calculations and in simplified gate circuit analysis, the equivalent gate circuit capacitance denoted as C_G is used, defined as follows:

$$C_{\mathrm{G}}={\displaystyle \frac{Q_{\mathrm{G}}}{V_{\mathrm{G}\mathrm{S}}}}.$$

(3)

However, the issue of equivalent C_G capacity is more complex due to different methods of its determination, e.g., based on charge or time equivalence [11,16].

The second very important parameter of the MOSFET gate circuit is the gate resistance R_G. The value of the R_G resistance together with the driver output resistance R_OUT determines the rate of the gate voltage increase and affects the power of the P_G losses in the transistor gate. Typical values of this resistance for MOSFETs are in the range from 1 Ω to 2 Ω and are the result of using polysilicon in the gate structures and internal connections of low-power MOSFETs [7,9,16]. In the case of power MOSFETs used at high frequencies up to 30 MHz, the gate resistance creates problems with their control. Typical gate resistances for power transistors have been reduced several times in the technological process by using the so-called gate metallization process, which significantly affect the price of the transistor.

The next chapter of this article presents a simple simulation model of the gate driver—the MOSFET transistor subcircuit—which was used to illustrate the problem resulting from overcharging the internal gate capacitance C_G of the MOSFET transistor and the associated power losses. The model parameters were selected based on the author’s previous research [5,16] and are reflected in real electronic components, which is explained in the next chapter.

Currently, there are many ready-made gate MOSFET driver solutions dedicated to high-frequency applications on the market. However, most of these circuits are designed to operate at a maximum frequency of 1 MHz or to work with low-power MOSFET transistors. Gate drivers that can operate in the ISM (Industrial, Scientific, Medical) frequency band [15,16,17], where the power MOSFET transistor is used, e.g., in a class D or DE inverter in a high-temperature plasma generation system (13.56 MHz), are difficult to obtain and constitute only a fraction of a percent of all integrated gate MOSFET drivers available. The simplest class E resonant inverter requires the use of only one MOSFET transistor. To ensure a high efficiency of the inverter, the transistor requires a stable operating point and optimal switching related to conditions (ZVS—Zero Voltage Switching, ZCS—Zero Current Switching) [15,16,17]. As the switching frequency of the MOSFET increases, problems increase, including with maintaining optimal switching, full and sufficiently fast reloading of the gate’s internal capacity and power losses occurring during switching. As mentioned earlier, in order to minimize the impact of frequency on the MOSFET switching process, dedicated and specialized driver systems, commonly called MOSFET drivers or gate drivers, are used. These systems ensure the most effective switching of the transistor gate with a specific (set) frequency and duty cycle depending on the required operating point of the MOSFET transistor [5,9,14,16,17]. In sum, the main task of gate drivers is to ensure the most effective transistor switching (with minimal losses) and they should be characterized by the shortest possible switching times.

There are many ready-made integrated MOSFET driver solutions available on the market with a wide range of frequencies. Low-power integrated MOSFET drivers, dedicated to applications with frequencies up to several dozen kilohertz (kHz), are characterized by short switching times and propagation times, but they are not suitable for applications above several megahertz (MHz). The reason for this is usually a too-low peak output current and allowable power losses. Integrated drivers dedicated to frequencies above a dozen or so megahertz are characterized by a much higher value of permissible power losses (even several dozen watts), and their switching times range from a few to a dozen or so nanoseconds.

The subject of this article focuses on characterizing and presenting the basic properties and parameters of high-frequency (MHz) MOSFET drivers operating in systems with power up to several kilowatts (kW). The problems of appropriate control of the gate of the MOSFET transistor and all aspects related to it are discussed. Moreover, the article presents and characterizes the latest commercial integrated gate driver IXRFD631 from IXYS operating in the frequency range up to 30 MHz. The MOSFET driver has been tested for two operating states: in the idle state (no load) and at the gate load of a DE275-501N16A series MOSFET transistor. The obtained laboratory results were compared with three other commercial integrated drivers: DEIC420, DEIC515 and IXRFD630 (which are the base structures) and two previous solutions of the author (4xUCC27516 and 8xUCC27526). One of the mentioned gate driver structures (8xUCC27526) of my own design is also presented in this article. Additionally, this paper presents the characteristics of power losses and efficiency, measurements of switching and propagation times of the tested gate drivers for maximum operating frequencies. Also, this paper presents the output voltage waveforms of integrated driver IXRFD631 and discrete driver 8xUCC27526 for two operating states. In addition, the work contains measurements of the parameters of the MOSFET driver treated as a four-way device, which has not been found in the literature, as a result of which parasitic parameters such as output inductance, output resistance and output capacitance were determined. Measurements were carried out using a precision impedance analyzer.

Analyzing the state of the literature, both around the world and within the country, it can be concluded that this work complements and systematizes the area of knowledge regarding both control issues of power MOSFET transistors, as well as introduces new elements regarding the design, implementation and measurement verification of MOSFET drivers with megahertz (MHz) operating frequencies.

2. The Simulation Model of the Gate Driver—MOSFET Transistor Subcircuit

In the case of the most commonly used transistor gate control with a rectangular voltage v_G, the gate-source voltage waveform v_GS may differ significantly from the voltage waveform (v_CG) on the internal capacitance of the gate C_G. Figure 1 shows the MOSFET transistor gate circuit, which was modeled for the following parameters:

• Parasitic inductance of the MOSFET transistor: L_G = 1 nH and L_S = 0.5 nH;
• Resistance and gate capacitance of the MOSFET transistor: R_G = 0.3 Ω and C_G = 4.17 nF;
• Resistance and output inductance of the gate MOSFET driver: R_OUT = 0.4 Ω and L_OUT = 3 nH;
• Resistance and inductance of the connection between the gate driver and the MOSFET transistor: R_P = 0.1 Ω and L_P = 3 nH.

The values of the L_G, L_S and R_G parameters were adopted as for the MOSFET transistor marked DE275-501N16A [18]. The parasitic inductances of the L_G gate, L_D drain and L_S source depend on the length and configuration of the transistor’s internal leads and the type of its housing. For example, for the DE275 series MOSFET transistor marked 501N16A, they are L_G = 1 nH, L_D = 1 nH and L_S = 0.5 nH [16,18]. These values can be estimated with great approximation based on the relationship:

L ≈ 7 ÷ 10 nH/cm.

(4)

Figure 2 shows the waveforms of the voltages and currents in the gate driver–MOSFET transistor subcircuit for different frequencies. The simulation tests of the gate driver–MOSFET transistor subcircuit were carried out in the ANSYS Electronics 2022 R2 (Simplorer) software.

The presented waveforms show that as the frequency increases, the method of overcharging the gate capacitance C_G of the transistor T changes. Initially, for a low switching frequency (Figure 2a), the overload of the gate capacitance is impulsive, but as the frequency increases, the RMS value of the gate current I_G(RMS) increases (Figure 2c). Power losses in the gate of a MOSFET transistor can be determined from the following relationship:

$$P_{\mathrm{G}}=I_{\mathrm{G}\left(\mathrm{RMS}\right)}^2\cdot R_{\mathrm{G}},$$

(5)

and the power losses in the driver itself will be equal to

$$P_{\mathrm{D}\mathrm{R}}=I_{\mathrm{G}\left(\mathrm{RMS}\right)}^2\cdot R_{\mathrm{O}\mathrm{U}\mathrm{T}}.$$

(6)

Table 1. The example parameters of the gate driver–MOSFET transistor subcircuit.

Parameters	Unit	Value
f	MHz	1	10	20
IG(RMS)	A	0.76	2.38	4.0
PG	W	0.18	1.69	4.8
PG + PDR	W	0.41	3.96	11.2

shows example parameters of the gate subcircuit from Figure 1.

Analyzing the data accumulated in Table 1, it can be seen that a two-fold increase in frequency (from 10 MHz to 20 MHz) corresponds to an approximately three-fold increase in power losses both in the transistor gate circuit itself and in the driver.

The numerical experiment is described below, as a result of which the power loss characteristics in the P_DR driver, the P_G transistor gate and the total losses in the entire P_DR + P_G circuit were plotted from frequencies in the range from 10 MHz to 30 MHz (model parameters as before).

As can be seen from the characteristics (Figure 3), the power losses initially increase with increasing frequency. This course of characteristics is, of course, not the rule. In this case, for a switching frequency of approx. 28.5 MHz, there is a local maximum of power losses, which corresponds to the resonant frequency of the driver–transistor circuit. The RMS value of the gate current I_G(RMS) of the MOSFET reaches its maximum value. On the one hand, this may be an advantageous operating state of the circuit, because overcharging the gate capacitance C_G at the resonant frequency allows the MOSFET to switch quickly. On the other hand, an excessive increase in the v_CG voltage at the transistor gate may be unacceptable. To reduce the voltage v_CG to an acceptable value (and the power losses in the circuit), the supply voltage V_G must be reduced.

Figure 4 shows the characteristics of power losses in the P_DR driver, the gate of the P_G transistor and the total losses in the entire P_DR + P_G circuit for frequencies in the range from 10 MHz to 30 MHz at a limited voltage (V_CGmax = 12 V) on the equivalent gate capacitance C_G of the MOSFET transistor.

Limiting the voltage across the gate’s equivalent capacitance from C_G to 12 V resulted in a significant reduction in the total P_DR + P_G power losses in the driver–transistor circuit. For the resonant frequency of the circuit in Figure 1, which is 28.5 MHz, the power losses has decreased by about 7 W.

In the next sections of this article, selected designs of the tested gate drivers will be discussed and research on their power losses will be presented.

3. Description of the Integrated IXRFD631 Gate MOSFET Driver

In this chapter, the basic information about of integrated hard-switching driver IXRFD631 produced by IXYS Corporation is provided. Figure 5 shows the schematic diagram of this MOSFET driver.

This integrated driver was produced as a successor to earlier versions such as DEIC420, DEIC421, DEIC515 and IXRFD630. All previous versions of integrated gate drivers have been available for sale for over a dozen years. The new version of integrated driver IXRFD631 (according to the manufacturer) is specifically designed to drive MOSFETs in Class D and E applications as well as other applications requiring ultrafast rise and fall times or short minimum pulse widths.

The most important part of this driver is the output stage with a complementary pair (T₁, T₂) of MOSFETs, usually with n and p channels. Additionally, the internal structure of the IXRFD631 driver uses the fast logical buffer, which controls the complementary pair (T₁, T₂) of output stage MOSFETs. The internal structure of the driver shown in the Figure 5 also includes the capacitor C, which acts as an energy bank reducing total power consumption.

Figure 6 shows the real photo of the IXRFD631 driver. Analyzing Figure 6, it can be seen that the hard-switching driver IXRFD631 is characterized by a flat, low-induction housing marked DE275. The same housing was used for older versions of, e.g., DEIC420, DEIC515 and IXRFD630 drivers.

This housing DE275 is characterized by a thermal pad that allows for quite effective heat dissipation (R_thJC = 0.25 °C/W) and large, metalized electrodes (leads) with a length of approx. 10 mm. Moreover, there is pin compatibility (pin-to-pin matching) between the discussed integrated driver and dedicated MOSFET transistors from the same manufacturer, e.g., DE275-501N16A. Additionally, this driver has double power supply voltage and ground terminals, which significantly facilitates the design of the gate circuit, and the symmetry of these terminals reduces the value of parasitic inductances.

4. Description of the Gate MOSFET Driver Designed by the Author

In this chapter, the basic information about the discrete hard-switching driver 8xUCC27526 designed by the author of this article is provided. Figure 7 shows the schematic diagram of the discrete driver marked as 8xUCC27526. The second discrete circuit 4xUCC27516 of the MOSFET driver was made in a similar way.

Analyzing Figure 7, it can be seen that the discrete driver 8xUCC27256 was constructed with the use of four UCC27526 low-power integrated drivers [16,20]. Each of the UCC27526 chips include two internal fast drivers, the switching times of which are less than 6 ns, and the maximum output current is 5 A. The construction of driver uses a total of eight low-power drivers connected in parallel, according to the circuit diagram shown in Figure 7—from here the name of this driver. The input stage of this driver uses the 74LVC2G34 logical buffers, which are necessary due to the permissible output load of the external control signal generator.

A single UCC27526 chip is closed in a WSON-8 type housing, with a dimension of 3.15 × 3.15 mm [20]. This is very important, because this housing allows the heat to be removed from the integrated circuit quite efficiently thanks to the thermal pad located on the lower side of housing. Thermal resistance between the junction and the solder pad is 9.5 °C/W. The real photo of this driver 8xUCC27526 is presented in Figure 8.

Analyzing Figure 8, it can be seen that the hard-switching driver 8xUCC27526 was made on a special PCB made of IMS (Insulated Metal Substrate) material in thermal clad technology [21]. Thermal clad is a dielectric (ceramic–polymer blend) coated metal base with a bonded copper circuit layer. This unique material offers superior heat transfer to help cool components while eliminating the problems associated with fragile ceramics. Thermal clad is a unique, three-layered system comprised of the following three layers (Figure 9):

• Circuit layer: This is the printed circuit foil with thickness of 1oz to 10oz (35–350 μm) in standard thermal clad.
• Dielectric layer: This offers electrical isolation with minimum thermal resistance. The multi-layer dielectric is the key element of thermal clad, and bonds the base metal and circuit metal together. The dielectric has UL recognition, simplifying agency acceptance of final assemblies.
• Base layer: This is often aluminum, but other metals such as copper may also be used. The most widely used base material thickness is 0.062’ (1.6 mm) in aluminum, although many thicknesses are available. In some applications, the base layer of metal may not be needed.
• More information about this technology can be found in the literature [16,21]. The PCB layout of the described discrete driver has dimensions of 50 × 60 mm and was made on a ProtoMAT LPKF C40 numerical milling machine.

5. The Experiment Results of All Tested MOSFET Drivers

The following drivers were tested in the laboratory: four integrated drivers available on the market (DEIC420, DEIC515, IXRFD630 and IXRFD631) and two discrete drivers (4xUCC27516, 8xUCC27526). Discrete drivers were designed by the authors of this article. The discrete drivers have been described, among others, in papers [4,5,9,10,16]. The laboratory tests of the MOSET drivers included power loss analysis, output voltage waveforms, propagation and switching times measurement and parasitic parameters. The laboratory tests were performed for two operating states of drivers: in the idle state (no load) and at the load gate for the output of driver by the MOSFET transistor. The main task of the tested drivers in these operating states was to overload (charge and discharge) the gate of a MOSFET power transistor DE275-501N16A (V_DS = 500 V; I_Dmax = 16 A; Q_G = 50 nC). More information about this MOSFET transistor can be found in [16,18]. Figure 10 shows the diagram of the measurement system used to determine the basic properties of all tested MOSFET drivers.

Below is a list of the equipment used and measurement conditions:

• Tested gate MOSFET drivers: integrated (DEIC420, DEIC515, IXRFD630 and IXRFD631) [19,22,23,24] and the author’s own construction (4xUCC27516 and 8xUCC27526) [4,5,9,10,16,20].
• All gate drivers tested for two operating modes: no-load operation and work under load of the DE275-501N16A transistor gate (not powered).
• All tested gate drivers powered from +12 V DC from a Motech LPS-302 power supply.
• External waveform generator Keysight 33611A (the operating frequency was set in the range from 10 MHz to 30 MHz, every 2.5 MHz; duty cycle of the control signal was 50%).
• Oscilloscope Tektronix TDS620B with probe P6139A (oscilloscope probe connected briefly to minimize parasitic parameters).
• Digital multimeters SANWA PC5000 (measurement of input current and voltage).
• Digital power voltage supply Motech LPS-302 (supply voltage value +12 V).
• Digital thermal camera FLIR E5-XT.
• Ambient temperature T_A = 25 °C.
• The measurements were carried out for the steady state of the driver’s temperature.

Measurements were carried out at a supply voltage value of the drivers V_SUP = 12 V; switching frequencies were in the range of 10 to 30 MHz, set from an external generator. The power loss characteristics in the idle state for all tested drivers is shown on Figure 11 in the second part of this article. Figure 12 shows the characteristics of power losses for all tested drivers (integrated and discrete) at load by the MOSFET transistor.

Figure 13 and Figure 14 show the output voltage waveforms for, respectively, the integrated driver IXRFD631 and discrete driver 8xUCC27526 in two operating states. The oscilloscope measurement of the output voltage was carried out using the “Pin-Pin” method (for a short time) using the Tektronix P6139A probe (500 MHz, 8.0 pF, 10 MΩ, 1.3 m). The output voltage waveforms for other compared gate divers can be found among others in the literature [4,5,9,10,16]. Additionally, Figure 15 presents a photograph of the drivers loaded with the gate of a MOSFET captured with a thermal camera. The voltage waveforms (Figure 13 and Figure 14) and the picture from a thermal camera (Figure 15) were obtained at the maximum operating frequency of 30 MHz.

Analyzing Figure 13a, it can be seen that the integrated driver IXRFD631 in the idle state at 30 MHz is characterized by a quasi-rectangular output voltage waveform of a maximum value of 18 V and a duty cycle value of 70%. This high-output voltage value allows full control of the gate of a MOSFET transistor, e.g., DE275-501N16A. Figure 13b shows the output voltage waveform of the driver IXRFD631, loaded with a MOSFET gate. The maximum value of the output voltage waveform of the driver is 16 V, and the shape of the output voltage is quasi-sinusoidal with a duty cycle of 40%.

Analyzing Figure 14a, it can be seen that the new discrete driver system in the idle state at 30 MHz is characterized by a rectangular output voltage waveform with a maximum value of 15 V and a duty cycle value of 41%. This high-output voltage value allows full control of the gate of a MOSFET transistor, e.g., DE275-501N16A. Figure 14b shows the output voltage waveform of the discrete driver 8xUCC27526, loaded with a MOSFET gate. The maximum value of output voltage waveform of driver is 15 V, and the shape of the output voltage is quasi-sinusoidal.

The operating temperature in a steady state for integrated driver IXRFD631 (Figure 15a) is approx. 134 °C. In the datasheet of the integrated driver, the manufacturer IXYS states that the maximum possible temperature for these drivers is 150 °C [19]. Analyzing the thermal photograph (Figure 15b), it can be noticed that the highest temperature is on the low power elements UCC27526, and the temperature value is approx. 128 °C. The maximum possible operating temperature of UCC27526 is 140 °C [16,18], so the new discrete driver can be used in, e.g., class E inverters for a long term.

Additionally, during the laboratory tests, the switching times of all drivers were also measured for both rising (L-H) and falling (H-L) edges. Measurement for switching times was performed for all drivers in the idle state (no load), with an operating frequency of 30 MHz and from 10% to 90% of the maximum value of output voltage signal. The switching times test results are given in

Table 2. The switching times measurement for all tested drivers.

Type of Driver	Symbol	Switching Times
		tR(L-H)	tF(H-L)
Integrated	DEIC420	3.6 ns	3.7 ns
Integrated	DEIC515	2.2 ns	2.9 ns
Integrated	IXRFD630	2.1 ns	12.0 ns
Integrated	IXRFD631	1.8 ns	3.3 ns
Discrete	4xUCC27516	1.1 ns	1.2 ns
Discrete	8xUCC27526	1.6 ns	1.2 ns

.

Propagation times were measured as well, for both rising (L-H) and falling (H-L) edges. The propagation times test results are shown in

Table 3. The propagation times measurement for all tested drivers.

Type of Driver	Symbol	Propagation Times
		tP(L-H)	tP(H-L)
Integrated	DEIC420	3.1 ns	1.1 ns
Integrated	DEIC515	8.0 ns	8.9 ns
Integrated	IXRFD630	7.9 ns	2.9 ns
Integrated	IXRFD631	5.2 ns	3.7 ns
Discrete	4xUCC27516	9.8 ns	10.2 ns
Discrete	8xUCC27526	15.0 ns	12.3 ns

. Measurement for propagation times was carried out for all drivers in the idle state (no load), between the output voltage signal and input signal from the generator, at a switching frequency equal to 30 MHz, and 50% duty cycle. The switching and propagation times measurement methods are compatible with the measurements given in datasheets of integrated drivers available on the market.

Additionally, the parasitic parameters such as series output resistance R_OUT, series output inductance L_OUT and parallel output capacitance C_OUT were measured for all tested drivers. Each of these parameters was determined using an Agilent 4294A impedance analyzer with the 16047E probe [25]. This analyzer allows impedance measurement in a wide range of frequencies (from 40 Hz to 110 MHz), and the impedance measurement method is the Auto Balancing Bridge [16,25] method. Figure 16 shows the simplified measurement scheme of drivers parasitic parameters. The parasitic parameters test results for all drivers are given in

Table 4. The basic parasitic parameters measurement for all tested drivers.

Type of Driver	Symbol	Parasitic Parameters
		ROUT, mΩ	LOUT, nH	COUT, pF
Integrated	DEIC420	469	4	1260
Integrated	DEIC515	5900	7	127
Integrated	IXRFD630	1240	6	562
Integrated	IXRFD631	375	4	641
Discrete	4xUCC27516	105	2	214
Discrete	8xUCC27526	135	3	595

.

The output resistance R_OUT represents all component resistances in the driver and gate circuits, both parasitic and additionally enabled. These include the resistance of the PCB tracks, the resistance of the output stage transistors and the resistance of the transistor’s gate. The output capacity C_OUT represents the equivalent gate capacity C_G of MOSFET transistor or the capacity between tracks of PCB layout for the discrete driver of MOSFET. The output inductance L_OUT is the sum of all inductances included in the gate circuit.

The last step of the laboratory research was to determine the efficiency characteristics of the tested MOSFET drivers. To determine the characteristics, it is necessary to know the output parasitic parameters (mainly the output resistance R_OUT) and the gate resistance R_G of the MOSFET transistor which was used as a load in determining the power loss characteristics from Figure 11. The method for determining the efficiency of gate drivers has been described in more detail among others in the works [16,26] and results from the inability to perform measurements other than those presented in this article and literature [16,26]. This problem results from a very short connection (often less than 1 cm in length) of the driver output to the gate of MOSFET. In conclusion, designating and determining idle (no load) power losses and load losses are the only measurements that can be performed in the driver–MOSFET circuit.

The R_G gate resistance of the DE275-501N16A series MOSFET is 371 mΩ and was determined on the Agilent 4294A impedance analyzer [16,25,26] for a maximum frequency of 30 MHz. Figure 17 shows the efficiency characteristics of the tested gate drivers. Based on the power loss characteristics (Figure 11 and Figure 12), the knowledge of the parasitic output resistances R_OUT of the drivers (Table 4) and R_G transistor in accordance with the relationship (4), the efficiency characteristics were plotted (Figure 17).

$$\eta ={\displaystyle \frac{\left(P_{\mathrm{L}\mathrm{T}}-P_{\mathrm{N}\mathrm{L}}\right)·\left(\frac{R_{\mathrm{G}}}{R_{\mathrm{G}}+R_{\mathrm{O}\mathrm{U}\mathrm{T}}}\right)}{P_{\mathrm{L}\mathrm{T}}}}·100\%$$

(7)

where

• P_LT—power losses of the drivers operating under the load of the MOSFET (Figure 12);
• P_NL—power losses of the drivers operating at idle state (no load) (Figure 11);
• R_G—gate resistance of the DE275-501N16A MOSFET transistor that is the load for the tested drivers (R_G = 371 mΩ);
• R_OUT—parasitic output resistance of the tested drivers (Table 4).

Analyzing the efficiency characteristics of the tested drivers from Figure 17, it can be seen that the integrated IXRFD631 driver has a quite low efficiency of approx. 70% in the frequency range from 22 MHz to 30 MHz. Below 22 MHz, the efficiency of this driver drops to approx. 30%. Moreover, its efficiency characteristics show some local extremes, which indicate the phenomenon of resonance (between parasitic parameters of the driver and the transistor) for higher, odd harmonics of the signal supplied from the external generator.

Figure 17. The efficiency characteristics of the tested drivers.

Figure 17. The efficiency characteristics of the tested drivers.

6. Conclusions

This article presents the performance, property analysis and experimental research determining power losses in the hard-switching MOSFET driver IXRFD631 operating in the frequency range up to 30 MHz. Additionally, this article presents the comparative characteristics of power losses for two operating states (no load and with load gate MOSFET DE501N16A) of the various hard-switching MOSFET drivers: commercial (DEIC420, DEIC515, IXRFD630 and IXRFD631), and the author’s own design (4xUCC27516 and 8xUCC27526). All the mentioned MOSFET drivers have been tested for, as follows:

-

Power losses for two operating states and efficiency in the frequency range up to 30 MHz;

-

The measurements of switching and propagation times for maximum operating frequency (30 MHz);

-

The measurements of the output parasitic parameters (L_OUT, C_OUT and R_OUT);

-

The output voltage waveforms for maximum operating frequency (30 MHz).

As shown, the power losses of the IXRFD631 driver are approx. 15 W—when operating at the idle state (no load) at a frequency of 30 MHz. These power losses are about 5 W lower compared to the DEIC515 and IXRFD630 integrated drivers, and about 19 W lower compared to the DEIC420 driver. If the output of the IXRFD631 driver is loaded with the gate of the MOSFET DE275-501N16A series, the power losses of the this driver increase the level of approx. 43 W and are still the lowest among the considered integrated drivers. The efficiency of the integrated driver IXRFD31 oscillates between 20% and 40%—for frequencies from 10 MHz to 20 MHz and between 60% and 70%—for frequencies from 22 MHz to 30 MHz. Comparing the switching and propagation times of all the analyzed drivers, it can be seen that the use of capacitor banks in the internal structure of the IXRFD631 driver and other modifications to the internal structure of the driver brought a good result:

-

Switching times of approx. 1.8 ns (t_R(L-H)) and 3.3 ns (t_F(H-L));

-

Delays of approx. 5.2 ns (t_P(L-H)) and 3.7 ns (t_P(H-L)), are fully acceptable for operation at a frequency of 30 MHz.

An alternative to commercial MOSFET driver systems are discrete solutions presented in this article. For example, the 8xUCC27526 discrete gate driver has power losses of 4 W (for no load operation) and 20 W for operation under a MOSFET gate load for a maximum operating frequency of 30 MHz—Figure 11 and Figure 12. By comparing the switching times (Table 2) and parasitic parameters (Table 4) of all tested MOSFET drivers, it can be seen that discrete solutions consisting of low-power components do not differ significantly from commercial solutions from IXYS.

The cost of manufacturing the 8xUCC27526 driver is much lower than the available price, e.g., IXRFD631 integrated driver solutions.

Therefore, when designing a power electronics converter, e.g., a class DE inverter for induction heating operating at a frequency of, e.g., 13.56 MHz, the costs of purchasing or manufacturing one’s own gate driver should be taken into account, and the range of the total efficiency of the system should be carefully considered. The use of commercial systems, e.g., IXRFD631, as shown in the paper, may result in a decrease in the efficiency of the entire converter. In the case of implementation of industrial electronics systems, where very high total efficiency is required (at a megahertz operating frequency), it is a better solution to develop one’s own MOSFET driver system than to use commercial, ready-made systems.

The next stage of work on gate MOSFET drivers will concern comparative tests on the next circuits of integrated drivers, e.g., IXRFD632, IXRFD615 and IXRFD615x2. Then, selected types of gate drivers will be tested on a real resonant inverter, e.g., class E (30 MHz, 300 W) or class EF (20 MHz, 400 W). Measurements will be carried out to include total and drain efficiency of the inverter, and the conduction and switching losses of the MOSFET-driver subcircuit will be determined. In addition, comparative laboratory tests of all MOSFET drivers are taken into account when their outputs are loaded with different capacitances, e.g., 3 nF and 6 nF, for the frequency range from 1 MHz to 45 MHz.