Power integrations LinkSwitch-4 LNK4*15D Series Application Note page 8

Application Note
Step 3 – Core and Bobbin Selection Based on Output
Power and Enter A
These symbols represent core effective cross-sectional area A
core effective path length L (cm), core ungapped effective inductance
E
A (nH/Turn ), bobbin width B (mm) and safety margin width M (mm).
2
L W
Due to the small transformer size that results at these power levels,
triple insulated wire is generally used for the secondary, so Safety
Margin Width is not used and left set to the default '0' setting. If the
Safety Margin method is preferred and standard wire used, enter the
safety margin width. The spreadsheet will double it and subtract it
from the bobbin width (B ) and give the effective bobbin width, or
W
winding width (B ). Universal input designs typically require a total
WE
margin of 6.2 mm, and a value of 3.1 mm entered into [B42]. The
spreadsheet uses the value of B
eter to fill the available bobbin width to minimize leakage inductance.
For designs using triple-insulated wire it may still be necessary to
enter a small margin to meet required safety creepage distances.
Typically many bobbins exist for each core size, each with different
mechanical spacing. Refer to the bobbin data sheet or seek guidance
from your safety expert or transformer vendor, to determine the
requirement for your design. The margin reduces the available area
for windings, so margin construction may not be suitable for
transformers with smaller cores. If, after entering the margin, more
than three primary layers (L) are required, either select a larger core
or switch to a zero-margin design using triple-insulated wire.
If the drop down selection menu in [B35] is used and 'AUTO' selected,
the spreadsheet selects the smallest core size, by A
peak flux density limit. The user can select an alternative core from
drop down list of commonly available cores (shown in Table 6). Table 5
provides guidance on the power capability of specific core sizes.
If the user has a preferred core not in the list, then the appropriate
parameters can be entered into [B36 – B42].
ENTER TRANSFORMER CORE/CONSTRUCTION VARIABLES
Core Type
Custom Core (Optional)
Bobbin
AE
LE
AL
BW
M
BWE
Figure 7. Transformer Core Selection.
8
Rev. B 10/17
, L , A , B , M
E E L W
E
to calculate the required wire diam-
WE
, that meets the
E
EPC17
Core Size
EF12.6
(cm ),
2
EE13
EE16
EF20
Table 5. Output Power Capability of Commonly used Sizes in LinkSwitch-4
Designs.
EE10
EF12.6
EE13
E24/25
EE16
EE19
EE22
EEL16
EE16W
EEL19
EEL22
EE25
EEL25
EEL28
EER28
EER28L
EER35
EER40
EES16
EF16
EF20
EF25
EF30
Table 6. List of Cores Provided in LinkSwitch-4 PIXls Spreadsheet.
EPC17 Core Type
If Custom core is used - Enter Part number here
P/N: BEPC-17-1110CPH
0.23 cm^2 Core Effective Cross Sectional Area
4.02 cm Core Effective Path Length
1150 nH/T^2 Ungapped Core Effective Inductance
9.55 mm Bobbin Physical Winding Width
0 mm Safety Margin Width (Half the Primary to Secondary Creepage Distance)
9.6 mm Effective Bobbin Width
Output Power Capability
3.3 W
3.3 W
6.1 W
10 W
Transformer Core Size
EF32
EFD15
EFD25
EFD30
EI16
EI19
EI22
EI25
EI28
EI30
EI35
EI40
EPC17
EPC19
EPC25
EPC30
ETD29
ETD34
ETD39
EE42/21/15
EE55/28/21
EF32
AN-69
www.power.com