HV9923 Datasheet, PDF (7/10 Pages) Supertex, Inc – 3-Pin Switch-Mode LED Lamp Driver ICs

HV9921/HV9922/HV9923
Let us assume that the overall efficiency η = 0.7.
Select L1 68mH, I=30mA. Typical SRF=170KHz. Calculate
the coil capacitance.
C_L
=
1
L1⋅( 2π ⋅ SRF )²
=
1
68mH ⋅( 2π ⋅ 170KHz )²
≈ 13 pF
Switching power loss:
P_SWITCH
≈
1 _(264V
2 ⋅ 10.5µs
⋅ 31pF
+ 2 ⋅ 100mA ⋅ 20ns)^{⎛⎜⎝} 264V
− ^41V
0.7
⎞
⎟⎠
P_SWITCH ≈ 120mW
Step 2. Selecting D1
Usually, the reverse recovery characteristics of ultra-
fast rectifiers at I_F=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.
Select D1 MUR160 with V_R = 600V, t_rr ≈ 20ns (I_F=20mA,
I_RR=100mA) and C_J ≈ 8pF (V_F>50V).
Minimum duty ratio:
D_m = 41V /(0.7 ⋅ 264V ⋅ 2 ) ≈ 0.16
Conduction power loss:
P_COND = 0.25 ⋅ (20mA)² ⋅ 210Ω + 0.63 ⋅ 200µ A ⋅ 264V ≈ 55mW
Step 3. Calculating total parasitic capacitance using (3)
C_P = 5 pF + 5 pF + 13 pF + 8 pF = 31pF
Total power dissipation in HV9921:
P_TOTAL = 120mW + 55mW = 175mW
Step 4. Calculating the leading edge spike duration using
(4), (5)
T_SPIKE
=
264V ⋅ 2 ⋅ 31pF
100mA
+ 20ns
≈ 136ns
< T_{BLANK ( MIN )}
Step 6. Selecting input capacitor C_IN
Output Power = 41V ⋅ 20mA = 820mW
Select C_IN ECQ-E4104KF by Panasonic (0.1µF, 400V,
Metalized Polyester Film).
Step 5. Estimating power dissipation in HV9921 at 264VAC
using (8) and (10)
Figure 2. Universal 85-264VAC LED Lamp Driver
D2 D3
L_IN
C_IN2
C_IN
C_O
D4 D5
D1
AC Line
85-264V
VRD1
F1
U1
HV9921/22/23
C_DD
3 V_DD
DRAIN ¹
GND
2
LED₁ -LED₁₂
L1
7
NR092005