Magnetics Modeling In Spice Proximity Loss Workshop 2017/Ridley...Magnetics Modeling In Spice...
17
1 Magnetics Modeling In Spice Proximity Loss Dr. Ray Ridley www.ridleyengineering.com PSMA Magnetics Session
Transcript of Magnetics Modeling In Spice Proximity Loss Workshop 2017/Ridley...Magnetics Modeling In Spice...
11
Magnetics Modeling In Spice
Proximity Loss
Dr. Ray Ridley
www.ridleyengineering.com
PSMA Magnetics Session
2
The Biggest Problem with Magnetics Design
The single biggest issue with magnetics design is that 99.9% of engineers don’t
understand or apply proximity loss properly.
Example: Forward converter transformer
Winding loss if you don’t do proximity analysis:
1.04 W
Winding loss with full harmonic analysis
10.77 W
33
Proximity Effects Current Distribution
1
2
3
4
5
Relative Current Density (A)
Current into page
Current out of page
Core
44
1-Dimensional Field Solution from Dowell’s Equation
1
sinh 2 sin 2( )
cosh 2 cos 2iG
2
sinh cos cosh sin( )
cosh 2 cos 2iG
2 2
1
1
2
1(1 () 4 )( )
n
d w i i i i
i i
ii
i
G GP b l Hh
i
i
i ii
w
l
h
n IH
b
Mean turn length of layer
Porosity of layer (fill factor)
Height of layer
H field at boundary of layer
i
ii
h
Ratio of fields on either side of layer
Skin depth of layer including porosity
Normalized height of layer relative to skin depth
55
Proximity Loss Example
300 -
425 V
12 V 30 A100 kHz
Primary 51 turns 20 awg 3 layers
Secondary 5 turns 10 mil foil
66
Primary Proximity Loss
DC 0.097 Ohm100 kHz 2.42 Ohm
77
Primary Proximity Loss
Magnetics Test Setup
Clear Transformer Design
0
0.5
1
1.5
2
2.5
3
3.5
4
0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.018 0.020
Time (ms)
Switch Current (A)
88
Primary Proximity Loss
Magnetics Test Setup
Clear Transformer Design
0.010
0.100
1.000
10.000
100.000
10 100 1000 10000 100000 1000000 10000000 100000000
Resistance (Ohm)
Frequency (Hz)
Transformer Primary AC Resistance vs Frequency
DC Resistance = 0.09657
Ripple Frequency Resistance = 2.4239
Ohm
Ohm
99
Primary Proximity Loss
Magnetics Test Setup
Clear Transformer Design
0.010
0.100
1.000
10.000
100.000
10 100 1000 10000 100000 1000000 10000000 100000000
Resistance (Ohm)
Frequency (Hz)
Transformer Primary AC Resistance vs Frequency
DC Resistance = 0.09657
Ripple Frequency Resistance = 2.4239
Ohm
Ohm Transformer Primary Winding Proximity Model Transformer Secondary Winding Proximity Model
Proximity model active? 1 1=yes
Rac1 1.32 mΩ
Rac2 234.43 mΩ
Rac3 2938.35 mΩ
Rac4 6590.55 mΩ
Rac5 21402.18 mΩ
Lac1 41.39685 uH
Lac2 41.0829 uH
Lac3 29.89081 uH
Lac4 8.84732 uH
Lac5 2.55406 uH
1010
Primary Proximity Loss
Magnetics Test Setup
Clear Transformer Design
1111
Magnetics Test Setup
Clear Transformer Design
Primary Proximity Loss
1212
Secondary Proximity Loss 10 mil Foil
DC 0.00145 Ohm100 kHz 0.0102 Ohm
1313
Secondary Waveforms and Proximity Loss
0
5
10
15
20
25
30
35
40
0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.018 0.020
Time (ms)
Forward Diode Current (A)
1414
Secondary Proximity Loss
Secondary Winding
Primary Winding
0.0014569
0.0102
0.001
0.010
0.100
1.000
10 100 1000 10000 100000 1000000 10000000 100000000
Resistance (Ohm) Transformer Secondary AC Resistance vs Frequency
Frequency (Hz)DC Resistance =
Ripple Frequency Resistance =
Ohm
Ohm
1515
Secondary Proximity Loss Reduced Foil Thickness
10 mil Reduced to 5 mil Foil
10 mil Foil
2.93 W
1616
Secondary Proximity Loss Simulation
17
Winding Structure to Spice Model in 1 Step
Transformer Primary Winding Proximity Model Transformer Secondary Winding Proximity Model
Proximity model active? 1 1=yes
Rac1 1.32 mΩ
Rac2 234.43 mΩ
Rac3 2938.35 mΩ
Rac4 6590.55 mΩ
Rac5 21402.18 mΩ
Lac1 41.39685 uH
Lac2 41.0829 uH
Lac3 29.89081 uH
Lac4 8.84732 uH
Lac5 2.55406 uH
Transformer Secondary Winding Proximity Model
Proximity model active? 1 1=yes
Rac1 0.00 mΩ
Rac2 0.02 mΩ
Rac3 1.80 mΩ
Rac4 108.50 mΩ
Rac5 319.92 mΩ
Lac1 0.15451 uH
Lac2 0.15451 uH
Lac3 0.15451 uH
Lac4 0.14178 uH
Lac5 0.03818 uH
