Infineon XDPL8218, Руководство по конструкции

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Design Guide 7 of 48 V 1.0
2018-06-06
XDPL8218 design guide
For high power factor flyback converter with constant voltage output
Transformer design
As a result, the primary main winding inductance L
p
can be defined and calculated as:
𝐿
𝑝
=
𝑉
𝐴𝐶,𝑚𝑖𝑛(𝑝𝑘)
∙ 𝑁 ∙ (𝑉
𝑜𝑢𝑡,𝑠𝑒𝑡𝑝𝑜𝑖𝑛𝑡
+ 𝑉
𝑑
)
𝐼
𝑝𝑟𝑖(𝑝𝑘),𝑚𝑎𝑥
∙ 𝑓
𝑠𝑤,𝑚𝑖𝑛,𝑎𝑡,𝑃,𝑜𝑢𝑡,𝑓𝑢𝑙𝑙
∙ [𝑉
𝐴𝐶,𝑚𝑖𝑛(𝑝𝑘)
+ 𝑁 ∙ (𝑉
𝑜𝑢𝑡,𝑠𝑒𝑡𝑝𝑜𝑖𝑛𝑡
+ 𝑉
𝑑
)]
(3)
𝐿
𝑝
=
√2 ∙ 90 ∙ 3.2 ∙ (54 + 0.7)
2.606 ∙ 52 ∙ 10
3
∙ [√2 ∙ 90 + 3.2 ∙ (54 + 0.7)]
𝑳
𝒑
= 𝟓𝟒𝟒 𝝁𝑯
Based on core cross-sectional area, A
e
= 120.1 mm
2
and saturation flux density at 100°C, B
sat(T=100°C)
= 0.41 Tesla
for TDG PQ26/20 core with TPW33 material, the transformer primary main winding turns N
p
can be defined as:
𝑁
𝑝
≥
𝐿
𝑝
∙ 𝐼
𝑝𝑟𝑖(𝑝𝑘),𝑚𝑎𝑥
𝐴
𝑒
∙ 𝐵
𝑠𝑎𝑡(𝑇=100°𝐶)
∙ 𝐷
𝑓,𝐵𝑠𝑎𝑡
(4)
Where D
f,Bsat
is the derating factor to ensure the designed transformer maximum flux density B
max
is below
B
sat(T=100°C)
by a margin of (100 percent - D
f,Bsat
) from saturation, and it is typical to set D
f,Bsat
in the range of 85
percent to 95 percent for a margin of 5 percent to 15 percent from transformer core saturation.
Taking D
f,Bsat
= 90 percent, N
p
can then be calculated as:
𝑁
𝑝
≥
544 ∙ 10
−6
∙ 2.606
120.1 ∙ 10
−6
∙ 0.41 ∙ 90%
= 31.99
Based on the above, N
p
= 32 is selected.
The transformer secondary main winding turns N
s
can then be calculated as:
𝑁
𝑠
=
𝑁
𝑝
𝑁
=
32
3.2
𝑵
𝒔
= 𝟏𝟎
To ensure fast V
CC
supply takeover from the primary auxiliary winding for avoiding IC reset during start-up, and
also to be able to deliver peak gate-drive voltage V
GD,peak
of 12 V with high enough primary auxiliary winding V
CC
supply during steady-state, the minimum primary auxiliary winding demagnetization voltage V
a,min
is therefore
defined as 14 V. As a result, the recommended minimum primary auxiliary winding turns N
a,min
can be defined
and calculated as:
𝑁
𝑎,𝑚𝑖𝑛
=
𝑉
𝑎,𝑚𝑖𝑛
∙ 𝑁
𝑠
(𝑉
𝑜𝑢𝑡,𝑠𝑒𝑡𝑝𝑜𝑖𝑛𝑡
+ 𝑉
𝑑
)
=
14 ∙ 10
(54 + 0.7)
= 2.56
(5)
To ensure proper HV pin line synchronization, V
CC
voltage should be lower than 19 V, the maximum auxiliary
winding demagnetization voltage V
a,max
is therefore defined as 19 V. As a result, the recommended maximum
primary auxiliary winding turns N
a,max
can be defined and calculated as:
𝑁
𝑎,𝑚𝑎𝑥
=
𝑉
𝑎,𝑚𝑎𝑥
∙ 𝑁
𝑠
(𝑉
𝑜𝑢𝑡,𝑠𝑒𝑡𝑝𝑜𝑖𝑛𝑡
+ 𝑉
𝑑
)
=
19 ∙ 10
(54 + 0.7)
= 3.47
(6)
Based on the calculation results of equations (5) and (6), primary auxiliary winding turns N
a
= 3 is selected.
A secondary auxiliary winding is added to supply the operating voltage of the Secondary Side Regulation (SSR)
FB circuit, since its op-amp or shunt regulator’s maximum operating voltage is less than V
out,setpoint
of 54 V. The
recommended minimum secondary auxiliary winding turns N
a,sec,min
and recommended maximum secondary
auxiliary winding turns N
a,sec,max
can be defined respectively as per N
a,min
and N
a,max
, as shown below:
𝑁
𝑎,𝑠𝑒𝑐,𝑚𝑖𝑛
= 𝑁
𝑎,𝑚𝑖𝑛
= 2.56
(7)
𝑁
𝑎,𝑠𝑒𝑐,𝑚𝑎𝑥
= 𝑁
𝑎,𝑚𝑎𝑥
= 3.47
(8)
Based on the calculation results of equations (7) and (8), secondary auxiliary winding turns N
a,sec
= 3 is selected.