AN4070
DC-DC converter design
Doc ID 022934 Rev 1
17/53
The second major contribution to transformer losses is given by core losses. The value of
specific core loss, P
lm
, for an RM14 core operating at 35 kHz, 100 °C and with a maximum
flux density of 200 mT, is equal to 141 kW/m^3.
The total core loss is therefore given by the following equation:
Equation 32
8.
Transformer temperature rise:
Using the value of thermal resistance reported in
Table 6
, the maximum temperature
rise for the HF transformer is given by:
Equation 33
DC-AC converter design
The basic scheme of the DC-AC converter topology is depicted in
Figure 9
. MOS5 and
MOS6 are connected in one leg and switch at a frequency of 17.4 kHz. Two Schottky diodes
are connected to the drain of these two MOSFETs in order to inhibit the internal body diode.
Two external silicon carbide (SiC) diodes are therefore connected in anti-parallel for current
freewheeling while avoiding problems connected to reverse recovery at MOSFET turn-on.
MOS7 and MOS 8 are connected in the second leg and switch at grid frequency, either 50
Hz or 60 Hz. An LCL filter is connected to the mid-point of each inverter leg and is used to
interface the system to the grid. On the DC side a bank of four electrolytic capacitors is used
to store and deliver energy whenever this is required during normal operation.
Figure 9.
Basic scheme of the DC-AC converter
W
V
P
P
e
lm
Fe
9
.
1
10
14000
10
141
9
3
=
⋅
⋅
⋅
=
⋅
=
−
(
)
C
P
P
R
T
cu
Fe
th
°
=
⋅
=
+
⋅
=
Δ
62
.
37
09
.
2
18
