HV9921/HV9922/HV9923
Let us assume that the overall efficiency η = 0.7.
Switching power loss:
1
41V
Select L1 68mH, I=30mA. Typical SRF=170KHz. Calculate
the coil capacitance.
⎛
⎝
⎞
P
≈
264V ⋅31pF + 2 ⋅100mA⋅ 20ns 264V −
(
⎜
)
SWITCH
⎟
⎠
2 ⋅10.5µs
0.7
1
1
CL =
=
≈ 13pF
L1⋅(2π ⋅ SRF )2 68mH ⋅(2π ⋅170KHz)2
PSWITCH ≈ 120mW
Step 2. Selecting D1
Minimum duty ratio:
Dm = 41V /(0.7 ⋅ 264V ⋅ 2 ) ≈ 0.16
Usually, the reverse recovery characteristics of ultra-
fast rectifiers at IF=20~50mA are not provided in the
manufacturer’s data books. The designer may want to
experiment with different diodes to achieve the best result.
Conduction power loss:
P
= 0.25 ⋅ 20mA 2 ⋅ 210Ω + 0.63⋅ 200µ A⋅ 264V ≈ 55mW
(
)
COND
Select D1 MUR160 with VR = 600V, trr ≈ 20ns (IF=20mA,
IRR=100mA) and CJ ≈ 8pF (VF>50V).
Step 3. Calculating total parasitic capacitance using (3)
CP = 5 pF + 5 pF + 13pF + 8 pF = 31pF
Total power dissipation in HV9921:
P
= 120mW + 55mW = 175mW
TOTAL
Step 6. Selecting input capacitor CIN
Output Power = 41V ⋅ 20mA = 820mW
Step 4. Calculating the leading edge spike duration using
(4), (5)
264V ⋅ 2 ⋅31pF
TSPIKE
=
+ 20ns ≈ 136ns < TBLANK( MIN )
Select CIN ECQ-E4104KF by Panasonic (0.1µF, 400V,
Metalized Polyester Film).
100mA
Step 5. Estimating power dissipation in HV9921 at 264VAC
using (8) and (10)
Figure 2. Universal 85-264VAC LED Lamp Driver
LIN
LED1 -LED12
D2
D4
D3
D5
CIN
CIN2
CO
D1
U1
L1
AC Line
85-264V
VRD1
F1
HV9921/22/23
1
DRAIN
3
VDD
CDD
GND
2
NR092005
7
SUPERTEX [ Supertex, Inc ]
