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Resonant LLC Converter: Operation and Design
14
Application Note AN 2012-09
V1.0 September 2012
݀
݀ܨ
ܭ
(
ܳ
௔௫
, ݉, ܨ
௑௠
)
ೌೣ
., .
= 0 ܨ
௑௠
= 0.489
݂
_
= ܨ
௑௠
݂
= 48.9݇ܪݖ
Step 4: Voltage Gain Verification
Since the power is derated at lower input voltages as listed in the specifications, we have to calculate the
maximum Q value at the minimum input voltage case (ܳ
௔௫@௏௠
), as follows. Note that this power derating
specification is related to the solar panel I-V characterestics. (In case of other applications where power
rating is the same across the input voltage range, we only have a single Qmax value).
ܳ
௔௫@௏௠
= ܳ
௔௫
ܸ
_
ܸ
_ ௔௫
= 0.2
Then we can calculate the maximum gain reached at the minimum switching frequency for the ܳ
௔௫@௏௠
condition, or we can look it up from the gain plot as shown in Figure 5.2.
ܭ
௔௫
= ܭ
(
ܳ
௔௫@௏௠
, ݉, ܨ
௑௠
)
= 1.974
ܭ
௔௫
= 1.974 > ܯ
௔௫
= 1.833 No need for tuning the m value
Figure
5
.
Step 5: Calculating Resonant Components Values
The reflected load resistance at full load is,
ܴ
_
=
8
ߨ
ܰ
ܰ
ܸ
௨௧
ܲ
,
ܴ
_
= 3.534
Next we solve the equations below to obtain the resonant tank components values
ܳ
௔௫
= 0.4 =
ܮ
/ܥ
3.534
݂
= 100݇ܪݖ=
1
2ߨ
ܮ
ܥ
݉ = 6.3 =
ܮ
+ ܮ
ܮ
ܮ
= 2.25ߤܪܮ
= 11.93ߤܪܥ
= 1.13ߤܨ
0.489
0.1 1 10
0
1
2
3
K .2 m Fx( )
K .3 m Fx( )
K .4 m Fx( )
Fx
1.974
Q
max
=0.4
Q
max@Vmin
=0.2