Page 25 - PEN eBook May 2023

DESIGN SEMICONDUCTORS

categorization is similar, a closer look shows that the the parallel of the GS66516B GaN HEMT. The threshold
distribution losses in the case of GaN are different voltage was observed to be nearly constant with
from those of silicon MOSFETs. changes in temperature, but transconductance had
a negative dependency on temperature. This results
In the case of GaN HEMTs, static or conduction losses in an automatic junction-temperature–balancing
include the R DS(on) loss at 25°C, R DS(on) loss from the mechanism: When the junction temperature increases,
heating effect, R DS(on) loss from the trapping effect (also the switching losses decrease considerably. In parallel
known as dynamic R DS(on) loss) and deadtime loss. The silicon-based MOSFETs, unlike GaN, the switching
switching loss includes turn-on/turn-off V-I overlap losses increase as the junction temperature increases,
loss and E qoss and E losses. Another kind of loss which can lead to unbalanced temperature distribution
oss
observed at very high frequency of operation is the or even thermal runaway.
C capacitance hysteresis loss, which is considered
oss
for a radio-frequency range of applications. The V-I To experimentally verify the above automatic
overlap loss is caused by the overlapping of the junction-temperature–balancing mechanism, the
current and voltage during switching operations. E is junction temperature of the parallel GaN HEMTs is
oss
the capacitance charging loss, i.e., the energy lost in measured. The experiment was conducted using a SiC Technology Is
charging the parasitic capacitance of the switch. E qoss is 240-A/650-V half-bridge power module with an IMS
the loss caused due to the capacitor charging current substrate built using randomly selected GaN HEMTs.
of the opposite switch in a half-bridge configuration of A full power emulation of the circuit at different Revolutionizing
HEMTs. switching frequencies showed excellent
junction-temperature balancing for paralleled GaN
While a significant amount of research has been done HEMTs. Electrification Trends
on the effect of static losses on the paralleling of
HEMTs, this article focuses on evaluating the switching
losses that can be as high as static losses in high- By Maurizio Di Paolo Emilio, editor-in-chief of Power Electronics News
voltage and high-frequency applications.
While silicon has been the go-to semiconductor With the 1,700-V EliteSiC MOSFET (NTH4L028N170M1),
ANALYTICAL MODELS AND material for the devices used in power-electronic onsemi delivers higher breakdown-voltage (BV)
EXPERIMENTS FOR ESTIMATING converters worldwide for quite some time, the SiC solutions, required for high-power industrial
LOSSES invention of silicon carbide in 1891 brought about an applications. The two 1,700-V avalanche-rated
The piecewise linear model is one of the most alternative to alleviate the dependency on silicon. SiC EliteSiC Schottky diodes (NDSH25170A, NDSH10170A)
popular models for analyzing and estimating the is a wide-bandgap (WBG) semiconductor: The energy allow designers to achieve stable high-voltage
losses of a transistor. The model considers the circuit required to excite an electron into the conduction operation at elevated temperatures while offering
only in terms of the input capacitance and external band is higher, and this wide bandgap has multiple high efficiency enabled by SiC.
gate resistor and ignores the parasitic parameters advantages compared with standard Si-based
and temperature dependency. Hence, it cannot be devices. In an interview with Power Electronics News, Ajay
used for analyzing the switching losses in a parallel Reddy Sattu, director of product marketing IPS BU
GaN configuration. Many researchers have worked on As a result of having a smaller leakage current and a at onsemi, noted that there are two key application
modifying the piecewise linear model to account for greater bandgap, a device may operate across a wider areas onsemi is focusing on with EliteSiC technology:
more dynamics in the circuit. To effectively monitor the temperature range without breaking down or losing energy infrastructure and electric vehicles.
switching losses, the piecewise linear model has been efficiency. This has further solidified SiC’s importance
modified to include parasitic elements and the effects in the field of power electronics and contributed to According to Sattu, energy infrastructure is the first
of the synchronous transistors. a surge in its use, together with the fact that it is one where bidirectional power flows to connect
chemically inert. large-scale storage systems with commercial or
To see the effect of temperature on losses, the utility-scale solar inverters.
variation of threshold voltage and transconductance is Thermal finite element analysis simulation results of GaN SiC power devices are currently being widely used
plotted with a change in the junction temperature of HEMTs on the IMS substrate (Source: IEEE) for applications like power supplies, “Bidirectional power flow flexibility means
battery-electric–vehicle (BEV) power conversion for round-trip efficiency is an important metric; as
battery charging and traction drives, industrial motor such, even a modest 0.5% improvement in efficiency
drives and renewable-energy–generation systems like generally results in a significant amount of energy
Reference solar and wind power inverters. that would be generated at the utility-scale level,”
Sattu said. “Let’s consider a typical solar application
The new 1,700-V EliteSiC MOSFET and 1,700-V where the DC output voltage is boosted to a 1,100-V
▶ 1Lu, J., Hou, R., & Chen, D. (2018). “Loss Distribution among Paralleled GaN HEMTs.” 2018 IEEE Energy avalanche-rated EliteSiC Schottky diodes have the DC bus and then inverted to a three-phase AC. Here,
Conversion Congress and Exposition (ECCE), pp. 1914–1919. goal to provide reliable, high-efficiency operation in in Figure 1, the boost stage can be implemented by
energy infrastructure and industrial drive applications. using a full-IGBT [Si IGBT + diode] module solution

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