Coilcraft Planar Transformer Prototyping Kit User manual

Planar Transformer
Prototyping Kit
Designer’s Kit C356
®

Contents
Introduction ................................................................................................. 1
Kit Contents ................................................................................................ 2
Part Details ................................................................................................. 2
Core........................................................................................................ 3
Primary Boards ...................................................................................... 3
Secondary Stamps ................................................................................ 4
Auxiliary Boards ..................................................................................... 5
Pins and Insulators ................................................................................ 7
Designing the Prototype ............................................................................. 7
General .................................................................................................. 7
Prototype Specifics ................................................................................ 9
Assembling the Prototype .......................................................................... 9
Sample Transformer ................................................................................. 10
Description ........................................................................................... 10
Assembly Procedure............................................................................ 11

PlanarTransformer Prototyping Kit Document 355 Revised 05/19/08 1
Introduction
The Coilcraft Prototype Planar Transformer Kit is used by Coilcraft designers to
provide fast turnaround of planar transformer samples. The kit allows the engi-
neer to experiment with the number of turns, DCR, and the location of the
windings within the assembly (interleaving). The pre-designed windings allow
quick evaluations and designs that are ready-to-go for production. The proto-
type can be assembled, placed in the circuit and tested, with no tooling.
With this kit, you can design planar transformers for the following topologies
and approximate power levels, based on 100 kHz switching frequency.
Full bridge and half bridge – 140 Watt
Push pull converter – 100 Watt
Forward converter – 50 Watt
Flyback – 25 Watt
The prototype transformers can have up to 12 primary turns and four second-
ary turns. Effective core area is 0.473 cm2. Complete specifications for the core
are listed on page 3. Primary to secondary isolation of the production parts is
1500 Vdc.
For engineers who prefer to build the planar magnetics and experiment, this kit
is a very valuable tool. Each kit contains a sufficient number of parts to build as
many as six prototypes. After a transformer design proves successful, the de-
sign can be submitted to Coilcraft. A sample transformer is built to be tested in
circuit before a production run is started.
This document describes all the parts in the kit and provides information that
covers assembling a prototype planar transformer or inductor. It does not offer
information regarding design criteria. It is assumed that the engineer has a
design concept and that the prototype will be used as a tool for testing.
A sample prototype is included, and may be used as a model.The core halves
of the sample are held together with tape. Production planar magnetics manu-
factured by Coilcraft are permanently glued.
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2
Kit Contents
The Prototype Planar Transformer Kit contains the following parts:
Core ....................................................................................................... 12 halves
Primary Boards .......................................................................... 4 each of 4 types
Auxiliary Boards ......................................................................... 4 each of 6 types
Secondary Stamp 1 ........................................................................................... 24
Secondary Stamp 2 ........................................................................................... 12
Insulator Washers ............................................................................................. 35
Large Pins ......................................................................................................... 35
Small Pins ......................................................................................................... 35
3/8″Tape (3M #1205) ..................................................................... Approx. 50 cm
Super Glue .................................................................................................. 1 tube
Metallic Marking Pen ........................................................................................... 1
One completed sample (48 V to 3.3 V / 30 A) built according to the assembly
procedure on page 11.
Part Details
The completed prototype consists of a windings assembly and two core halves,
as shown in Figure 1.The windings assembly is a combination of Primary Boards,
Secondary Stamps, Insulator Washers, and if needed, an Auxiliary Board.
Each design requires a unique number of boards and stamps. The number
and orientation of the boards and stamps are dependent on the turn counts
and required DCR rating.
An insulator washer is used between each part of the windings assembly and
between the windings assembly and each core half.
Windings
assembly
Bottom
core half
To p
core half
Figure 1. Major Components of a Planar Transformer
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PlanarTransformer Prototyping Kit Document 355 Revised 05/19/08 3
Core
This kit contains 12 core halves. Two pieces are needed for each prototype.
The cores are not gapped. Specifications are as follows:
Effective area (Ae) = 0.473 cm2; Minimum area (Amin) = 0.410 cm2
Effective magnetic path length (Ie) = 2.64 cm
Effective volume (Ve) = 1.25 cm3
ALvalue for core set = 2500 nH/turns2
Relative permeability = 1500 nom
Weight: 5.2 g per set (2 halves)
Primary Boards
The four different Primary Boards can be combined in series (for more turns)
or in parallel (for lower DCR). The kit includes Primary Boards with 3 turns,
4 turns, 5 turns and 6 turns.The following primary turns are possible:
3 Turns
4 Turns
5 Turns
6 Turns
6 Turns (3 Turns + 3 Turns)
8 Turns (4 Turns + 4 Turns)
9 Turns (5 Turns + 4 Turns)
10 Turns (5 Turns + 5 Turns)
11 Turns (6 Turns + 5 Turns)
12 Turns (6 Turns + 6 Turns)
Using two 6 Turn Primary Boards in parallel results in half the DCR of using
one 6 Turn Primary Board.
When using two Primary Boards in series, one board is inverted and the boards
are connected together only at pin 3. Boards used in parallel are oriented the
same way (the layers of each board face the same direction) and are con-
nected together at pins 2 and 3 or at pins 3 and 4 when both are inverted.
Each Primary Board marked with the number of turns on layer 2.
3 Turns Primary Board (equivalent to 24 AWG, typical DCR = 10 m⏲)
5
4
3
2
1
6
7
8
9
10
10
9
8
7
6
1
2
3
4
5
3T
Layer 1 Layer 2
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4
4 Turns Primary Board (equivalent to 25 AWG, typical DCR = 18 m⏲)
5
4
3
2
1
6
7
8
9
10
10
9
8
7
6
1
2
3
4
5
4T-P
Layer 1 Layer 2
5 Turns Primary Board (equivalent to 26 AWG, typical DCR = 26 m⏲)
5
4
3
2
1
6
7
8
9
10
10
9
8
7
6
1
2
3
4
5
5T-P
Layer 1 Layer 2
6 Turns Primary Board (equivalent to 27 AWG, typical DCR = 40 m⏲)
5
4
3
2
1
6
7
8
9
10
10
9
8
7
6
1
2
3
4
5
6T
Layer 1 Layer 2
Secondary Stamps
Each Secondary Stamp is one turn. Stamps can be combined in series up to a
total of four turns.The stamps can also be connected in parallel for lower DCR.
Stamp 1 and Stamp 2 are identical electrically. Use the stamps that provide the
pin connections suitable for your application.
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PlanarTransformer Prototyping Kit Document 355 Revised 05/19/08 5
When using two stamps in series, one stamp is inverted when building the
windings assembly. Each stamp is the equivalent of 16.5 AWG.
Secondary Stamps (typical DCR = 0.9 m⏲)
10 or 6
9 or 7
9 or 7
8
Stamp 1 Stamp 2
Auxiliary Boards
The Auxiliary Boards are suitable for most applications without the need to
make combinations. The six auxiliary boards in the kit are:
2 Turns
3 Turns
4 Turns
5 Turns
7 Turns
9 Turns
Each Auxiliary Board is marked with the number of turns on layer 2.The Auxiliary
Board should be positioned at the top or bottom of the windings assembly.
2 Turns Auxiliary Board (typical DCR = 16 m⏲)
5
4
3
2
1
6
7
8
9
10
10
9
8
7
6
1
2
3
4
5
2T
Layer 1 Layer 2
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6
3 Turns Auxiliary Board (typical DCR = 85 m⏲)
5
4
3
2
1
6
7
8
9
10
3T
Layer 2
10
9
8
7
6
1
2
3
4
5
Layer 1
4 Turns Auxiliary Board (typical DCR = 82 m⏲)
5
4
3
2
1
6
7
8
9
10
10
9
8
7
6
1
2
3
4
5
4T
Layer 1 Layer 2
5 Turns Auxiliary Board (typical DCR = 140 m⏲)
5
4
3
2
1
6
7
8
9
10
10
9
8
7
6
1
2
3
4
5
5T
Layer 1 Layer 2
7 Turns Auxiliary Board (typical DCR = 165 m⏲)
5
4
3
2
1
6
7
8
9
10
10
9
8
7
6
1
2
3
4
5
7T
Layer 1 Layer 2
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PlanarTransformer Prototyping Kit Document 355 Revised 05/19/08 7
9 Turns Auxiliary Board (typical DCR = 250 m⏲)
5
4
3
2
1
6
7
8
9
10
10
9
8
7
6
1
2
3
4
5
9T
Layer 1 Layer 2
Pins and Insulators
The pins are used to interconnect the boards and stamps and to surface mount
the completed transformer to the PCB. An insulator must be used between
each part of the windings assembly and between the windings assembly and
each core half.
The Small Pins (0.038″diameter) are used for pins 1–5 and connect all the
primaries and auxiliary windings. The Large Pins (0.058″diameter) are used
for pins 6–10 and connect all the secondary stamps.
Small pin Large pin Insulator
Designing the Prototype
General
There are many combinations of boards and stamps that may be used in a
design. The total number of parts that can be used in a windings assembly is
limited by the core size. The cores can accommodate a windings assembly
up to 5 mm high, including top and bottom insulators. Maximum thickness of
each part is as follows: Primary boards: 0.64 mm; Auxiliary boards: 0.32 mm;
Stamps: 0.46 mm, Insulators: 0.05 mm. Some of the combinations of parts
that fit in the core are:
4 Primary Boards, 1 Auxiliary Board and 2 Stamps
2 Primary Boards, 1 Auxiliary Board and 4 Stamps
1 Primary Board, 1 Auxiliary Board and 6 Stamps
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8
Familiarize yourself with each of the parts in the kit and determine the correct
combination of parts needed to build your prototype. Before beginning the as-
sembly take note of the pin connections for each layer of all the boards you
plan to use.
Each Primary Board winding connects to pins 2 and 3. An inverted primary
board connects to pins 4 and 3.
Secondary Stamp 1 connects to pins 7 and 8. An inverted Stamp 1 connects
to pins 8 and 9. Secondary Stamp 2 connects to pins 9 and 10. An inverted
Stamp 2 connects to pins 6 and 7.
Each Auxiliary Board connects to pins 1 and 5.
A typical schematic showing pin connections is shown in Figure 2. A typical
dimensional drawing and recommended land pattern is show in Figure 3.
9
2
3
Pri
Aux
7
4
1
5
8
Sec
Figure 2. Typical Schematic
Land pattern shown is for all pins being used. If pins are not
used in the transformer, omit pads from the pattern.
0.800
20,32
Recommended
Land Pattern
0.125
3,18
0.095
2,41
0.095
2,41
Ø0.110
2,79
Ø0.080
2,03
2
1
3
10
6
7
8
9
4
5
0.360
9,14 max
0.810
20,57 max
0.920
23,37 max
0.006 /0,15
2
1
3
4
56
8
9
7
10
Dot indicates pin 1
Figure 3. Typical Dimensional Drawing
Note: By using stamps as the primary
and primary boards as the sec-
ondary, a step-up transformer,
up to 1 :12 turns ratio, can be
created.
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PlanarTransformer Prototyping Kit Document 355 Revised 08/26/08 9
Prototype Specifics
Determine how many Primary Boards and Secondary Stamps are needed to
satisfy the number of turns in the design.
The number of turns for the primary winding can be determined by using the
following equation:
N = V × t × 108
Ae× B
where:
N = number of turns
V = Voltage
t = time = (1 ÷ frequency) × duty cycle
Ae= core area = 0.473 cm2
B = flux density (Gauss)
The amount of current the prototype can handle depends on the number of
stamps used in the secondary. Each stamp is the equivalent of 16.5 AWG.
Refer to the diagrams of the Primary Boards and Stamps and take note of the
typical DCR rating of each. If the DCR requirement is met, the prototype can be
built. If the DCR of the primary is higher than desired, double the number of
Primary Boards and connect them in parallel. If the DCR of the secondary is
higher than desired, double the number of stamps. Keep in mind the maximum
number of parts that can fit in the core.
Primary turns ________ Required DCR ________
Secondary turns ________ Required DCR ________
Auxiliary turns ________
Current handling ________
Assembling the Prototype
Select all the parts needed to build the prototype, including an insulator washer
to be used between each part of the prototype. The following points should be
taken into account in order to assemble a prototype that will closely match the
final production planar component.
•To minimize leakage inductance, make sure that the boards, stamps and
insulators are sandwiched tightly together. The tighter all the parts are to
each other, the lower the leakage inductance.
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10
•Interleave parts as much as possible. Plan the placement of parts so that
Primary Boards are separated by Stamps. In the sample transformer, each
Primary Board is placed between two Stamps.The more interleaving that
can be accomplished, the lower the leakage inductance.
The following precautions must be observed when building a prototype.
• An Insulator must be used between each part of the windings assembly
and between the assembly and each half of the core. If an insulator is
missing, the transformer will short.
• All parts in the windings assembly must be assembled so the center holes
are concentric. If the pins securing the parts together are not perpendicu-
lar to all the boards and stamps, the winding assembly is skewed and an
internal short can occur.
•The completed windings assembly must be glued to the bottom core half.
If the assembly is allowed to float in the core, an internal short can occur.
Note: The winding assembly of the sample transformer is intentionally not
glued to the core. This allows the winding assembly to be removed
from the core to be studied.
Study the exploded view of the sample transformer and plan the order
and orientation of parts used in the prototype. Lay out all the parts in the
correct order and orientation. Review the assembly procedure for the
sample transformer. Once you are comfortable with the procedure, as-
semble your prototype.
Sample Transformer
Description
The sample transformer has a 12-turn primary and a 2-turn secondary. The
sample uses two stamps in parallel for each turn in order to lower DCR. It does
not have an Auxiliary Board. Figure 4 shows a schematic and top view of the
sample.
Note: The windings assembly of the sample transformer has not been
glued to the core. Feel free to remove the tape securing the core
halves and remove the windings assembly to inspect.
Primary turns 12 Required DCR 60 m⏲⏲
⏲⏲
⏲
Secondary Turns 2 Required DCR 0.9 m⏲⏲
⏲⏲
⏲
Secondary current 30 A
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PlanarTransformer Prototyping Kit Document 355 Revised 05/19/08 11
An exploded view of the sample transformer is show in Figure 5. The sample
transformer provided with the kit consists of the following parts:
•Two 6 Turn Primary Boards in series.
•Four stamps — two stamps in parallel for each turn in series.
•Seven insulators.
•Six pins (3 large, 3 small).
•One Core set (2 halves).
Assembly Procedure
Refer to Figure 5 and use the following procedure to assemble the sample
transformer.
1. Place one half of the Core on a clean working surface.
Note: Make sure that the centers of all parts are concentric.
2. Glue an insulator into the core.
3. Orient a Stamp 1 so that the terminals extend out of the core as shown in
the detail in Figure 5. Make sure the terminal holes will align with pins 7
and 8 of the Primary Board.
4. Place the stamp over the insulator.
5. Working from the bottom, insert two Large Pins (pins 7 and 8) into Stamp 1.
Note: The bottom of the pins must be flush with the bottom of the core in
order to surface mount the completed prototype.
6. Ensure the pins are positioned so they are flush with the bottom of the core
and solder them to Stamp 1.
7. Place an insulator over the stamp.
Figure 4. Sample Transformer
6T
10
9
8
7
6
1
2
3
4
5
2
12 : 2
3
Pri
4
8
9
7
Sec
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12
8. Position a 6 Turns Primary Board so that Layer 1 faces up. Align terminals
7 and 8 with the pins inserted into Stamp 1. Slide the board down over the
pins onto the insulator.
9. Working from the bottom, insert three Small Pins (pins 2 ,3 and 4) and one
Large Pin (pin 9) into the board.
Note: The bottom of the pins must be flush with the bottom of the core in
order to surface mount the completed prototype.
10. Solder all pins to the board.
11. Place an insulator over the board.
12. Orient another Stamp 1 in the same direction as Stamp 1 installed in step 3.
Slide the stamp down over pins 7 and 8 and onto the insulator over the
board.
13. Solder the stamp to pins 7 and 8 to complete one turn of the secondary.
14. Place an insulator over the stamp.
15. Invert a Stamp 1 and slide it down over pins 8 and 9 and onto the insulator.
Solder the stamp to pins 8 and 9.
16. Place an insulator over the stamp.
17. Position a 6 Turns Primary Board so that Layer 2 faces up. Align terminals
2, 3 and 4 with the small pins and terminals 7, 8 and 9 with the large pins.
Slide the board down over the pins onto the insulator.
18. Solder the board to all six pins.
19. Place an insulator over the board.
20. Invert a Stamp 1 and slide it down over pins 8 and 9 and onto the insulator
over the board.
21. Solder the stamp to pins 8 and 9 to complete the second turn of the
secondary.
22. Glue the windings assembly to the insulator in the bottom half of the core.
23. Place an insulator over the top stamp. Glue the insulator to the windings
assembly.
24. Align the top core half with the bottom core half making sure that the cores
are oriented in the same direction. Secure the core halves with about 8 cm
of tape.
25. Use the supplied marking pen and place a dot in the corner of the top core
to indicate pin 1.
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PlanarTransformer Prototyping Kit Document 355 Revised 05/19/08 13
Figure 5. Exploded view of the Sample Transformer
Core half
Large pins
Small pins
Stamp 1 inverted
(one half of second turn)
Stamp 1 inverted
(one half of second turn)
Stamp 1
(one half of first turn)
Stamp 1
(one half of first turn)
6 Turn Primary Board
6 Turn Primary Board
inverted
Core half
6T
Orientation of first Stamp 1
and bottom Core half
Insulator
Insulator
Insulator
Insulator
Insulator
Insulator
Insulator
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Coilcraft, Inc.
www.coilcraft.com
Worldwide Headquarters
1102 Silver Lake Road
Cary IL 60013 USA
[phone] Fax [phone]
inf[email protected]
European Headquarters
21 Napier Place, Wardpark North
Cumbernauld, Scotland G68 0LL
[phone] Fax [phone]
[email protected]
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