STEVAL-ILL013V1 Datasheet, PDF (38/43 Pages) STMicroelectronics – 80 W offline LED driver with PFC

UM0670
Design calculation
Resistor R202 limits the charging current and should be in the following range:
Equation 4
V_{GD MAX} – V_{ZCD CLAMP} – V_F
⎛ ^VGD
MIN
–
V
ZCD
CLAMP ^{– VF}⎞
-------------------------------------------------------------------------------
V_{ZCD CLAMP}
<
R ₂₀₂
< R₂₀₃ ×
⎜
⎝
----------------------_V----_Z---_C----_D-------_C---_L---_A----_M----_P-----------------------_⎠⎟
I_ZCD
MAX
+
----------------------------------
R ₂₀₃
Equation 5
-¹----⁵----–-----⁵---^.--⁷-----–----⁰----^.-⁷---
0.01
+
⎛
⎝
3^---5-9^--.-0^-7--0^{--⎠⎞}
<
R ₂₀₂
<
3900
×
⎛
⎝
9_----._-8_{-----–-----}55_---.._--77_{-----–----}0_---._--7_{--⎠⎞}
Equation 6
750 < R₂₀₂ < 2326
A 1 kΩ resistor is chosen for R202.
Capacitor C203 should be lower than 1.25 nF, and therefore a value of 220 pF was chosen:
Equation 7
C₂₀₃ < (C₂₀₄ | |
C₂₀₆
)
V_{ZCD CLAMP}
---------------------------------------------------------------------------------------
(V_{GD CMAX} – V_{ZCD CLAMP} – V_F)
=
1.89 ×
10^–9
--------------⁵---^.--⁷---------------
15 – 5.7 – 0.7
= 1.25nF
C₂₀₃ = 220 pF
Inductor size is calculated using following equation:
Equation 8
L = -------^V----^L---^E----^D-----^×-----^t--^O----^F---^F-------- = -⁸---⁰-----^×-----¹----⁶-----^×-----¹----⁰---^–---⁶- = 1.6mH
2 × (I_MAX – I_AVR) 2 × (1.4 – 1)
Two sense resistors are connected in parallel and their size is calculated:
Equation 9
R₂₀₄ | |
R₂₀₆
=
-^V----^C----^S---
I_MAX
=
1_----._-0_----8_--
1.04
=
0.77Ω
The output LED current of 1 A was precisely set by adjusting resistors R204 and R206, and
therefore their optimal resistance values are 1.5 Ω and 2.2 Ω.
R₂₀₄ = 1.5 Ω
R₂₀₆ = 2.2 Ω
In the next step the power MOSFET and its heat sink are calculated. The power MOSFET
RMS current is derived using the following equation:
Doc ID 15327 Rev 2
38/43