Design Guide
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V 1.0
2018-06-06
XDPL8218 design guide
For high power factor flyback converter with constant voltage output
HV pin-related design
7
HV pin-related design
As shown in
, HV series resistor R
HV
is connected from the HV pin to the cathodes of HV diode D
HV1
and
D
HV2
, while bridge rectifier AC input should be applied across the D
HV1
anode and D
HV2
anode.
Additionally, a HV capacitor C
HV
should also be connected between the HV pin and ground.
R
HV
HV
~ ~
C
HV
D
HV1
D
HV2
Bridge rectifier
`
Figure 9
HV pin, R
HV
, C
HV
, D
HV1
and D
HV2
connections
The recommended minimum HV series resistor value R
HV,min
is defined and calculated as:
𝑅
𝐻𝑉,𝑚𝑖𝑛
=
𝑉
𝑖𝑛,ℎ𝑖𝑔ℎ(𝑝𝑘)
𝐼
𝐻𝑉,𝑚𝑎𝑥
(21)
Where I
HV,max
is the HV pin maximum peak input current of 9.6 mA.
𝑅
𝐻𝑉,𝑚𝑖𝑛
=
√2 ∙ 326
9.6 ∙ 10
−3
= 48
kΩ
The recommended maximum HV series resistor value R
HV,max
is defined and calculated as:
𝑅
𝐻𝑉,𝑚𝑎𝑥
=
𝑉
𝐴𝐶,𝑚𝑖𝑛(𝑟𝑒𝑐𝑡,𝑎𝑣𝑔)
− 𝑉
𝑉𝐶𝐶𝑂𝑁,𝑚𝑎𝑥
𝐼
𝐻𝑉,𝑚𝑖𝑛(𝑎𝑣𝑔)
∙ [1 −
2
𝜋
∙ 𝑠𝑖𝑛
−1
(
𝑉
𝑉𝐶𝐶𝑂𝑁,𝑚𝑎𝑥
𝑉
𝐴𝐶,𝑚𝑖𝑛(𝑝𝑘)
)]
(22)
Where V
AC,min(rect,avg)
is the average value of the rectified V
AC,min
, while V
VCCON,max
is the maximum V
CC
turn-on voltage
threshold of 22 V, and I
HV,min(avg)
is the recommended HV pin minimum average input current of 1 mA.
𝑅
𝐻𝑉,𝑚𝑎𝑥
=
0.9 ∙ 90 − 22
1 ∙ 10
−3
∙ [1 −
2
𝜋
∙ 𝑠𝑖𝑛
−1
(
22
√2 ∙ 90
)]
𝑅
𝐻𝑉,𝑚𝑎𝑥
= 52.5 𝑘Ω
Based on the above, R
HV
= 52 kΩ is selected in this design example.
The HV series resistor dielectric withstand voltage should be above the total of V
AC,max(pk)
and V
margin,FET
(see
Section 4
for their respective values), which is equivalent to 521.3 V. As an example, the selected R
HV
= 52 kΩ in
this design example can be formed using a 36 kΩ 0.5 W resistor (dielectric withstand of 350 V) in series with a 16
kΩ 0.25 W resistor (dielectric withstand of 200 V).
For better line synchronization stability against noise interference, C
HV
shown in
is needed. In addition,
C
HV
also improves the surge and ESD capability of the HV pin.
C
HV
= 1 nF is recommended and selected in this design example.
