AN11486_15 Datasheet, PDF (39/53 Pages) NXP Semiconductors – GreenChip SSL8516T PFC and flyback controller

NXP Semiconductors
AN11486
GreenChip SSL8516T PFC and flyback controller
9. Large signal component values calculation
Table 3 shows the initial requirements of an LED driver as example.
Table 3. Initial design requirements
Requirement
Symbol Choice
Example
low input voltage V_ac(rms)min 90 V (AC)
high input voltage V_ac(rms)max 305 V (AC)
100 V; 10 % margin
277 V; +10 % margin
THD at 305 V (AC) can be compromised when
a 450 V bus capacitor is used
output voltage
output current
holdup time
V_o(min)
V_o(max)
I_o(min)
I_o(max)
t_holdup
16 V
48 V
160 mA
1.6 A
0 ms
V_o(max) : V_o(min) = 3 : 1
75 W; 10 % dimmable LED driver
lower output capacitance and bus capacitance
can be used when no hold up time is required
flyback MOSFET V_DS(fb)max 800 V
voltage rating
allows high N_fbV_o:
• lower voltage stress on the secondary
rectifier
• less turn on losses due to deeper valley
fast transient
-
support
no (CC output) a smaller C_bus can be used when no transient
support is required when PFC is switched off
9.1 Bus capacitor
For the bus capacitor value calculation, several constraints apply:
• Voltage rating
• OVP level on the VOSENSE pin
• Holdup time
• Auto PFC on/off with load step support
9.1.1 Voltage rating
The target is to use a single 450 V bus capacitor C4.
• V_{C4max} = 450 V
• V_{busavgPFCon} = V_{mainsrmsmax}  2 = 305 2 = 431 V
• V_{busrippleppmax} = 2V_{C4max} – V_{busavgPFCon} = 38 V
The minimum bus capacitance due to the allowed voltage ripple based on the C4 voltage
rating is:
C4_rating
=
----------------------------------------------------^V---^o---^--^m---^a---^x--^---^---^I---^o--^--^m----^a--^x---^---------------------------------------------------
2    f_{acmin}  V_{busrippleppmax}  V_{busavgPFCon}  _total
(33)
 C4_rating = ₂-----_---_-----_---₅---₀-⁴---⁸_---₃--^-₈--¹---^._-⁶--₄---₃---₁----_---₀---_.--₉- = 16.6 F
AN11486
Application note
All information provided in this document is subject to legal disclaimers.
Rev. 1 — 17 July 2014
© NXP Semiconductors N.V. 2014. All rights reserved.
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