Switch Mode Power Supply Transformers

Switch Mode Power Supply Transformers
Economy series features low-cost,
industry-standard sizes
Performance series features SMT and
low profiles
Power range from 1 watt to 1,200 watts
Frequency range to 500 KHz
Can be designed to meet UL, CSA,
VDE, CE or IEC standards
D E S I G N I N G
A N
S M P S
T R A N S F O R M E R
In designing a switch mode power supply, one of the most difficult but least understood elements is
the transformer. ICE’s goal is to simplify the transformer design process and thereby shorten the design
cycle time. The first step is to define the SMPS parameters. This should include the following items:
input voltage, secondary power output for each winding, switching frequency, I peak and the maximum
allowable duty cycle. You will also need to choose the type of switching topology that you plan to use.
Refer to ICE’s application note on pg. 17 for more information on switching topologies.
Next is the easy part. 1 You can turn to page 21, fill out the SMPS custom design form and fax it to
(703) 257-7547 or 2 Follow the step-by-step procedure on the next page to design your own SMPS
transformer. When finished, fill out the bottom section of the custom design form on page 21 and fax
it in. That’s it, you’re done! ICE will provide a quotation and samples and you can move on to other
aspects of your design.
G L O S S A R Y
PT-1
Np: Primary turn count
Ve: Effective volume
E-T: Volt-time product (Volt-microSecond)
mi: Initial permeability
B: Maximum flux density (Assume 3,000 Gauss)
E (l/A): Core factor
Ae: Effective cross sectional area
D max.: Maximum duty cycle
Ns: Secondary turn count
Vdc min.: Minimum rectified input line voltage
Vs: Output voltage
Po: Output power
Vd: Output rectifier and choke voltage drop
F: Frequency
Ac: Bobbin window area
PL: Power loss
AeAc: The product of Ae and Ac
I: The peak current in the winding
le: Magnetic path length
Lp: Primary inductance
ICE COMPONENTS, INC.
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PH 800-729-2099
Switch Mode Power Supply Transformers
D E S I G N
P R O C E D U R E
The following design procedure will aid in the design of transformers for flyback, forward and push-pull
topologies. The goal of the procedure is to get the engineer to a working prototype quickly. We have
made some basic assumptions in this design procedure that will work for most designs. If you feel your
application is more difficult than normal or you are designing a half or full bridge power supply we
suggest you fill out ICE’s custom design form on page 21 and let ICE engineers complete your design.
Before you get started, make a copy of ICE’s custom design form and fill in the input voltage,
secondary power output for each winding, switching frequency, I peak and the maximum allowable
duty cycle.
S T E P●
1
ST EP●
5
Core Choice—Make your preliminary core choice
based upon the power requirements of the
application, the switching topology that you have
chosen and the frequency. Refer to the graphs
starting on the next page for reference.
Secondary turns—Choose the exact primary and
secondary turn counts to be used based upon the
Np and Ns/Np.
S T E P●
2
E-T Value—Determine the E-T value based upon
the maximum allowable duty cycle and the
frequency. This formula will provide the answer
in V-uSec.
6
E-T= 1*10 (Dmax) (Vdc min.)
f
S T E P●
3
Primary turn count—Determine the minimum
number of primary turns required to support the
worst case (E-T) volt-time product. For an exact
value, use the formula below.
E-T * 102
Np =
B * Ae
*(Ae values are listed in the tables on page 12)
S T E P●
4
Turns Ratio—Calculate the second/primary
turns ratio.
Flyback
Ns
(Vs+Vd) (1-D)
=
Np Vdc min * Dmax
Forward Converter
Ns
Vs+Vd
=
Np Vdc min * Dmax
Push-Pull Converter
Ns
Vs
=
Np Vdc min * Dmax
ICE COMPONENTS, INC.
ST EP●
6
Primary inductance–Calculate the required primary
inductance.
eff(Vdc min * Dmax)2
2 * Po * F
Note: The efficiency, at this point in the design, is
an estimate. Use the following table to determine
the value.
Lp =
Topology
Flyback
Forward
Push-Pull
Efficiency Range
75%–80%
80%–85%
87%–92%
ST EP●
7
Air Gap—To calculate the air gap you must first
determine the AL value required to achieve the
primary inductance.
AL =
L
Np2
Air Gap =
1.257 - 1
le
(SL/A)*AL) mi *
The air gap can now be calculated with the
formula above.
Note: The push-pull and forward converter
topologies typically do not require an air gap.
ST EP●
8
Wire Size—Find the wire size from the table on
page 14. Assume 400 circular mils per one
ampere. Total circular mils = 400 * I.
ST EP●
9
Fit Factor—Calculate the required winding
window. The formula is: (wire dia.)2 * (# of turns)
for each winding. Add the total for all windings
and compare the total to the allowable space
(Ac) listed in the tables on page 12. Do not
exceed 75% fill.
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PH 800-729-2099
PT-2
Switch Mode Power Supply Transformers
P E R F O R M A N C E
PT-ER0905-XX
S E R I E S
PT-ER1406-XX
PT-EFD15-XX
PT-EFD20-XX
PT-EFD25-XX
PT-EFD30-XX
Ac (cm2)
0.0306
0.055
0.167
0.29
0.402
0.523
Ae (cm2)
0.0847
0.176
0.122
0.31
0.58
0.69
AeAc (cm4)
0.0026
0.0097
0.0204
0.0899
0.2332
0.3609
le (cm)
1.42
1.9
3.4
4.7
5.7
6.8
Ve (cm3)
0.12
0.33
0.51
1.46
3.3
4.7
mi
1800
S(l/A)mm-1
1800
1.67
E C O N O M Y
1800
1.08
2.27
1800
1800
1.52
1800
1.00
0.98
S E R I E S
PT-EE25/06-XX
PT-EE35/10-XX
PT-EE41/13-XX
PT-EE42/15-XX
PT-EE55/21-XX
Ac (cm2)
0.53
0.95
1.24
Ae (cm2)
0.39
0.89
1.61
1.84
2.4
3.46
AeAc (cm4)
0.2067
0.8455
1.9964
3.588
4.68
11.17
le (cm)
4.90
7.30
8.27
10.32
10.32
13.08
Ve (cm3)
1.93
5.59
17.3
34.2
44.0
mi
2000
S(l/A)mm-1
P O W E R
2000
1.24
V S
11.5
2000
0.85
0.517
1.95
PT-EE42/20-XX
1.95
2000
2000
0.548
F R E Q U E N C Y — F O R W A R D
3.23
2000
0.417
0.35
C O N V E R T E R
Performance
Series
1000
EFD30
100
EFD25
EFD20
EFD15
10
ER14.5/6
ER9/5
1
100kHZ
P O W E R
200kHZ
V S
300kHZ
400kHZ
F R E Q U E N C Y — F L Y B A C K
500kHZ
C O N V E R T E R
Performance
Series
1000
EFD30
100
EFD25
EFD20
10
EFD15
ER14.5/6
1
ER9/5
0.1
PT-3
100kHZ
200kHZ
ICE COMPONENTS, INC.
300kHZ
400kHZ
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500kHZ
PH 800-729-2099
Switch Mode Power Supply Transformers
P O W E R
V S
F R E Q U E N C Y — P U S H - P U L L
C O N V E R T E R
Performance
Series
1000
EFD30
100
EFD25
EFD20
EFD15
10
ER14.5/6
ER9/5
1
100kHZ
P O W E R
200kHZ
V S
300kHZ
400kHZ
F R E Q U E N C Y — F O R W A R D
500kHZ
C O N V E R T E R
Economy
Series
1000
EE55/21
100
EE42/20
EE42/15
EE41/13
10
EE35/10
EE25/6
1
20kHZ
P O W E R
50kHZ
V S
75kHZ
F R E Q U E N C Y — F L Y B A C K
100kHZ
C O N V E R T E R
Economy
Series
1000
EE55/21
100
EE42/20
EE42/15
EE41/13
10
EE35/10
EE25/6
1
20kHZ
50kHZ
ICE COMPONENTS, INC.
75kHZ
www.icecomponents.com
100kHZ
PH 800-729-2099
PT-4
Switch Mode Power Supply Transformers
P O W E R
V S
F R E Q U E N C Y — P U S H - P U L L
C O N V E R T E R
Economy
Series
10000
1000
EE55/21
EE42/20
100
EE42/15
EE41/13
EE35/10
10
EE25/6
1
20kHZ
50kHZ
W I R E S I Z E
AWG
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
PT-5
75kHZ
100kHZ
S P E C I F I C A T I O N S
BARE dia (in)
0.1019
0.0907
0.0808
0.072
0.0641
0.0571
0.0508
0.0453
0.0403
0.0359
0.032
0.0285
0.0253
0.0226
0.0201
0.0179
0.0159
0.0142
0.0126
0.0113
0.01
0.0089
0.008
0.0071
0.0063
0.0056
0.005
0.0045
0.004
0.0035
0.0031
0.0028
0.0025
ICE COMPONENTS, INC.
BARE dia (mm)
lb/1kft wt
2.58826
2.30378
2.05232
1.8288
1.62814
1.45034
1.29032
1.15062
1.02362
0.91186
0.8128
0.7239
0.64262
0.57404
0.51054
0.45466
0.40386
0.36068
0.32004
0.28702
0.254
0.22606
0.2032
0.18034
0.16002
0.14224
0.127
0.1143
0.1016
0.0889
0.07874
0.07112
0.0635
31.7
1.26
20
15.9
12.6
10
7.94
6.32
5.02
3.99
3.17
2.52
2
1.6
1.26
1
0.794
0.634
0.501
0.404
0.317
0.252
0.204
0.161
0.127
0.101
0.081
0.065
0.052
0.04
0.031
0.025
0.02
w w w. i c e c o m p o n e n t s . c o m
ohm/1kft res.
0.9985
1.261
1.588
2
2.52
3.18
4.02
5.05
6.39
8.05
10.1
12.8
16.2
20.3
25.7
32.4
41
51.4
65.3
81.2
104
131
162
206
261
331
415
512
648
847
1080
1320
1660
a. cir.mil
10380
8230
6530
5180
4110
3260
2580
2050
1620
1290
1020
812
640
511
404
320
253
202
159
128
100
79.2
64
50.4
39.7
31.4
25
20.2
16
12.2
9.61
7.84
6.25
PH 800-729-2099
Switch Mode Power Supply Transformers
M E C H A N I C A L
E R 9 / 5
E R 1 4 . 5
E F D 1 5
E F D 2 0
21.0 MAX
E F D 2 5
10.0 MAX
20.1+-0.3
22.0 MAX
1.0x0.4
25.5 MAX
13.5 MAX
26.5 MAX
3.76
29.7+-0.2
1.1x0.4
5.0
E F D 3 0
31.0 MAX
14.0 MAX
32.0 MAX
0.64
2.2+/-0.1
ICE COMPONENTS, INC.
5.0
27.0+/-0.2
www.icecomponents.com
PH 800-729-2099
PT-6
Switch Mode Power Supply Transformers
E E 2 5 / 0 6
E E 4 2 / 1 5
PT-7
ICE COMPONENTS, INC.
E E 3 5 / 1 0
E E 4 2 / 2 0
w w w. i c e c o m p o n e n t s . c o m
E E 4 1 / 1 3
E E 5 5 / 2 1
PH 800-729-2099