STEVAL-ILL013V1 Datasheet, PDF (40/43 Pages) STMicroelectronics – 80 W offline LED driver with PFC

UM0670
Design calculation
Power loss on the STPSC806D diode is:
Equation 17
P_{LOSS D}= I_{AVR D} × V_F= 0.8 × 0.7 = 0.56W
where forward diode voltage was found for the average diode current 0.8 A in the datasheet
(see datasheet Section 11: References and related materials: 4.).
Calculated junction diode temperature without using heat sink is:
Equation 18
T_J= P_{LOSS D} × (R_thJC + R_thCA) + T_A= 0.56 × (2.4 + 60) + 30= 65° C
Junction-to-case thermal resistance is available in the datasheet for the STPSC806D and
case-to-ambient temperature is determined by the device package used. In this case, the
TO-220 package is used and its thermal resistance is typically 60 °C / W.
Calculated junction diode temperature without using a heat sink is much lower than the
maximum junction temperature for the STPSC806D, and therefore this diode is suitable for
the design.
One of the most important things to consider is proper inductor design. The inductor size
was calculated in Equation 8, but generally the inductor size by itself is not enough to ensure
proper inductor design and therefore several additional equations are used for completing
overall inductor construction.
First, the inductor core size must be selected and for this selection it is very helpful to
calculate the minimum area product using application parameters. Minimum required core
area product (AP), where the flux swing is limited by core saturation is:
Equation 19
AP_MIN=
⎛
⎝
L_-----×_----B--l_{--PM---E--A--A-X--K---×--}×_---C--l_{--R-l---M----S--⎠⎞}
4_--
3
=
⎛
⎜
⎝
-₀---^1.-₃--^.--⁶-_×----^×--₄---¹²----⁰⁰---^–--_×-³----^×₀----_.-₅-¹---^.-_×-⁴-----^×₁---₀--¹--_–--₄- _{⎠⎟⎞}
4_--
3
=
0.2518cm⁴
where the constant is Cl = J_MAX x C_R x 10^–4 = 420 x 0.5 x 10^–4.
The inductor core E25 from EPCOS was selected. The minimum core cross section is 51.5
mm² and the winding cross section is 61 mm² (see datasheet Section 11: References and
related materials: 5.) and the calculated product area is:
Equation 20
AP= A_N × A_MIN= 61 × 51.5= 0, 31415cm⁴
The calculated product area is bigger than the minimum required product area, and
therefore the inductor core E25 can be used.
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