© 2012 Fairchild Semiconductor Corporation
30
FEBFAN9611_S01U300A
• Rev. 0.0.1
10.7.
Efficiency
Figure 41 and Figure 42 show the measured efficiency of the 300W evaluation board
with R
MOT
=60.4k
Ω
at input voltages of 115V
AC
and 230V
AC
. The phase management
threshold on the test evaluation board is approximately 15% of the nominal output power.
The threshold can be adjusted upwards to achieve a more desirable efficiency profile by
increasing the MOT resistor. Figure 43 and Figure 44 show the light-load efficiency
improvement that can be achieved when the threshold is adjusted to 30% by increasing
the MOT resistor to 120k
Ω
.
Since phase shedding reduces the switching loss by effectively decreasing the switching
frequency at light load, greater efficiency improvement is achieved at 230V
AC
, where
switching losses dominate. Relatively less improvement is obtained at 115V
AC
, since the
MOSFET is turned on with zero voltage and switching losses are negligible. The
efficiency measurements include the losses in the EMI filter, cable loss and power
consumption of the control IC.
Figure 41. Efficiency vs. Load (115V
AC
)
Figure 42. Efficiency vs. Load (230V
AC
)
Figure 43. Efficiency vs. Load (115V
AC
)
Figure 44. Efficiency vs. Load (230V
AC
)
90%
95%
100%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Effi
ci
e
n
cy
(%
)
Output
Power
(%)
Efficiency
vs.
Load
(115V
AC
,
400V
DC
Output,
R
MOT
=60.4K
Ω
,
No
Inrush
Circuit)
90%
95%
100%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Effi
ci
e
n
cy
(%
)
Output
Power
(%)
Efficiency
vs.
Load
(230V
AC
,
400V
DC
Output,
R
MOT
=60.4K
Ω
,
No
Inrush
Circuit)
90%
95%
100%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Ef
fi
ci
e
n
cy
(%
)
Output
Power
(%)
Efficiency
vs.
Load
(115V
AC
,
400V
DC
Output,
R
MOT
=120K
Ω
,
No
Inrush
Circuit)
90%
95%
100%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Ef
fi
ci
e
n
cy
(%
)
Output
Power
(%)
Efficiency
vs.
Load
(230V
AC
,
400V
DC
Output,
R
MOT
=120K
Ω
,
No
Inrush
Circuit)
