Datasheet

LV5026MC
No.A2042-7/16
Given that the period when current flows into coil is
DutyI =
T
_
c+T
_
d
T
Ipk ×
1
2
× (Duty × T)/T = ILED
Ipk ×
2 × ILED
DutyI
(1) since Ipk ×
VREF
_
IN
Rcs
Rcs ×
VFEF
_
IN
Ipk
=
DutyI × VFEF
_
IN
2ILED
(2)
Since formula for LED current is different between on period and off period as shown above,
Ipk ×
Vac-V
ƒ
L
× T_c =
V
ƒ
L
× T_d (3)
Since T_c + T_d = DutyI × T, T_c = DutyI × T - T_d (4)
Based on the result of (3) and (4), T_d = DutyI × T ×
Vac-V
ƒ
Vac
(5)
To obtain L from the equation (1), (3), (5),
L ×
V
ƒ × DutyI
2 × ILED
× DutyI × T =
Vac - V
ƒ
Vac
=
V
ƒ
2 × ILED
×
1
ƒ osc
×
Vac - V
ƒ
Vac
× (DutyI)
2
(6)
Since LED and inductor are connected in serial in non-isolation mode, LED current flows only when AC voltage exceed
VF.
Given that the ratio of inductor current to AC input is DutyAC.
DutyAC =
90 - arcsin (
V
ƒ
√
2Vrms
)
90
Since the period when the inductor current flows are limited by DutyAC, the formula (6) is represented as follows:
L =
V
ƒ
2 × ILED
×
1
ƒ osc
×
Vac - V
ƒ
V
IN
× (DutyI)
2
×
90 - arcsin (
V
ƒ
√
2Vrms
)
90
(7)
Ipk: peak inductor current
Vf: LED forward voltage drop
Vac: effective value(R.M.S value)
VREF: Built-in reference voltage (0.605V)
VREF_IN: REF_IN voltage (6 pin)
Rs: External sense resistor
Vzd: Zener diode voltage (REF_IN pin)
2
√2 × Vrms
VF
Vac
(AC voltage, R.M.S)
Inductor current
Arcsin (Vf/√2Vrms)
Arcsin (√2Vrms/√2Vrms)
=90 (Deg)
Arcsin (Vf/√2Vrms)