IEEE Power Electronics Magazine - September 2021 - 35

51 mm
eGaN FETs
Output Inductor
3.5 mm Thick, 2.4 µH
Housekeeping
Power Supply
Current
Sense
FIG 8 The EPC9148 converter fitted with the Würth Elektronik 7443762504022 2.2 µH inductor.
Experimental Verification
A three-level synchronous buck converter evaluation board,
the EPC9148 [18], was designed with a custom designed
inductor, the 7443762504022 [19]. The eGaN FETs used are
the 3.2 mΩ, 100 V rated EPC2218 and the 3.6 mΩ, 40 V rated
EPC2055 as shown Figure 1. The inductor measures 18 mm
× 25 mm and has an inductance of 2.2 µH with DCR of
1.96 mΩ and saturation current (|ΔL/L| < 30%) of 23.8 A with
total estimated losses when operating in the EPC9148 at full
load power of 1.5 W.
The EPC9148 converter fitted with the 7443762504022
inductor is shown in Figure 8. Various key elements of the
circuit have been highlighted in Figure 8, including a side
view showing that the total solution has a thickness of just
5 mm including the printed circuit board.
The converter efficiency, measured at steady state, of the
EPC9148 fitted with the Würth Elektronik 7443762504022
2.2 µH inductor operating with 48 V input and 19 V output
and 400 LFM airflow is shown in Figure 9. The results show
that the peak efficiency exceeds 98% at a load current of
9 A and the maximum component temperature is just 65 °C,
as shown in Figure 10. It should be noted that the inductor
temperature is a cool 45 °C, which represents only a 20 °C
temperature rise.
Conclusions
This article presented an ultra-thin 48 V to 19 V three-level
synchronous buck converter that can deliver up to 250 W
into the load with peak efficiency exceeding 98%. This converter
design was made possible by using the latest eGaN
FETs in combination with a custom designed inductor and
utilizing a three-level synchronous buck converter topology.
The success of the performance of the converter led to the
commercial release of the inductor.
Q4: 59° C
L: 45° C
24
FIG 10 Experimental thermal results of the EPC9148 converter
operating at 48 V input and delivering 19 V into the load and
cooled with 400 LFM airflow.
September 2021 z IEEE POWER ELECTRONICS MAGAZINE 35
Both the converter and inductor were designed synchronously
through an iterative process. The inductor only
experienced a 20 °C temperature rise at full load when the
converter was forced-air cooled at 400 LFM. This inductor
99
98
97
96
95
94
93
92
123456789 10 11 12 13
Output Current (A)
FIG 9 Experimental efficiency results of the EPC9148 converter
operating at 48 V input and delivering 19 V into the load.
°C
64.5
Q1: 58.5° C
Q2: 61° C
Q3: 65° C
Total System Efficiency (%)
40 mm
Maximum
Height 3.5 mm

IEEE Power Electronics Magazine - September 2021

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