EB205 Motorola GaAs Rectifiers Offer High Efficiency in a 1 ... - ECA

GaAs PERFORMANCE RESULTS
Performance results for output power levels of 73 watts to
460 watts are presented in Figures 2 through 5 and Tables 2
and 3.
In Table 1, shows how 10 amp, MGR1018 GaAs rectifiers
offer an advantage over silicon parts with a 20 amp current
rating. (Note: only one side of the silicon device was used
for equal comparison.) The efficiency gains of the GaAs
rectifiers decrease with output power somewhat due to its
larger forward voltage drop. However, the silicon devices
did not perform above 143 watts. This was attributed to the
large amount of ringing due the large reverse recovery peak
exhibited by the silicon devices. The peak current
generated a high voltage spike that in turn forced the
MBR20200 into a zener mode and destroyed the part.
Figure 2 shows the efficiency achieved from the
converter over a power output of 96 to 460 watts. The
switching frequency of the inductor was 1.2 MHz throughout
this power range. Through use of zero voltage switching by
the MC34067 IC and the fast recovery times of the rectifiers,
the converter was able to achieve efficiencies in excess of
91% with a maximum of 95.4%! Note that the increase in
GaAs efficiency in Figure 2 over Table 1 is due to the use of
both leads of the MGR1018 part in Figure 2. In Table 1, one
outer lead is connected on the single die MGR10180 (each
outer leg is attached to the single die) and only one outer
lead is connected on the dual die MBR20200. This allows
for comparison of a silicon MBR20200, die rated at 10 amps
(one half of device) to a 10 amp rated MGR1018. After
running the silicon comparison, both outer leads of the test
socket were connected for maximum efficiency realized in
Figure 2.
Table 1. Performance Benefits Realized
When Using GaAs versus Silicon Rectifiers
(400 Volts Input, 1.1 to 1.29 MHz Converter Frequency)
Output
Power
Center Tap
Si
MBR20200
Efficiency
Single
GaAs
MGR1018
Efficiency
GaAs
Advantage
73 Watts 81.6% 84.2% 2.6%
95 Watts 87.2% 91.2% 3.9%
119 Watts 91.4% 91.9% 0.5%
143 Watts 92.7% 92.7% 0.0%
96
MGR1018 Efficiency and Regulation at 375 Vdc Input Level
95.5
95.4%
95
94.5
94.5%
EFFICIENCY (%)
94
93.5
93
92.5
92
91.5
91
96 119 143 166 189 237 264 287 309 343 380 427 449 455 462
OUTPUT POWER (WATTS)
Figure 2. GaAs Offers High Efficiency at
Switching Frequencies Above 1 MHz
(Input Voltage Ranging from 375 Vdc to 405 Vdc)
2 MOTOROLA