Datasheet

0 55
Load Current - A
100
25
Efficiency - %
EFFICIENCY
vs
LOAD CURRENT
98
90
86
80
94
88
82
96
92
84
5 10 15 20 30 35 40 45 50
V
IN
= 400 V with L
RES
V
IN
= 350 V with L
RES
V
IN
= 300 V with L
RES
0 2.0
Load Current - A
12
0.8
Light-Load Power Losses - W
LIGHT-LOAD POWER LOSSES
vs
LOAD CURRENT
11
6
4
0
9
5
2
10
7
3
0.2 0.4 0.6 1.0 1.2 1.4 1.6 1.8
8
1
Burst Mode
DCM Mode
with Diode
Rectification
CCM Mode with
Synchronous FETs
UCC28950
www.ti.com SLUSA16B –MARCH 2010–REVISED OCTOBER 2011
Experimental Results Example
The following experimental results are based on 660-W output power prototype of phase shifted full-bridge
DC/DC converter. The input voltage is 300 V to 400 V and the output is 12 V, 55 A. The primary MOSFETs are
SPA11N60CFD and the synchronous rectifier MOSFETs are FDP047AN08A0, two in parallel. The measured
efficiency of the prototype is shown in Figure 51.
Figure 51. Efficiency of the Prototype Phase-Shifted Converter
(V
IN
= 300 V, 350 V and 400 V, V
OUT
= 12 V)
Because of the power saving need even at very light and no-load conditions, careful optimization of operation at
light load condition is required to set the proper boundaries between different operation modes. The result of this
optimization is shown in Figure 52. This plot demonstrates the power savings while moving from the synchronous
rectification mode above 1-A load current, into the discontinuous current mode with the diode rectification
between 0.3-A and 1-A load current, and eventually into the burst mode operation at load current below 0.3 A.
Figure 52. Power Losses of the Prototype at Light-Load and No-Load Conditions
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