CS1600_1007 Datasheet, PDF (11/18 Pages) Cirrus Logic – LOW-cost PFC Controller for Electronic Ballasts

CS1600
5. FLUORESCENT BALLAST APPLICATION EXAMPLE
The following section gives an example for a front-end PFC stage design for an electronic ballast application. The equations that
follow may be used as guidelines for any other requirements using the CS1600.
D5
L1
D6
BR1 BR1
R1a ^RAC
R1b
CS1600
AC
Mains
1
C1
R1c
NC
3
IAC
2
STBY
4
FB
+12V
7
VDD
6
R3
GD
BR1 BR1
C2 ⁸
NC
5
GND
R_FB
R2a
R2b
R2c
Q1
C3a ^Clink
C3b
Figure 17. CS1600 Basic Application Circuit
5.1 Component Selection Guidelines
The following design example is for a wide-input-voltage
fluorescent ballast application using 2 T5 lamps in series for a
total nominal power of 108W.The target specifications for the
PFC portion of the design, assuming a 94% efficient second
stage, are as follows:
V_in(min)
V_in(max)
V_link
P_o
η
108 VAC
305 VAC
460 V
115 W
95%
5.1.1 I_AC and I_FB Sense Resistors
The rectified line voltage, V_AC, and the output voltage of the
PFC boost converter, V_link, are scaled as currents by using
sense resistors, whose values are estimated based on the
equations below:
R_FB
=
V_{-----l-i--n--k----–-----}V_----d---d-
I_ref
R_FB
=
---⁴----⁶---⁰-----–----¹----²----
130 × 10^–6
[Eq.4]
R_FB = 3.45MΩ
R_AC = R_FB
R_AC = 3.45MΩ
[Eq.5]
where
R_FB = Feedback resistor used to reflect the PFC output
voltage
R_AC = Feedforward resistor used to reflect the rectified line
voltage
V_link= PFC Output Voltage
V_DD = IC Supply Voltage
I_ref = Target reference current used for feedback
1% or lower tolerance resistors are recommended to
maximize the tightly toleranced system behavior provided by
the unique digital controller in the CS1600. Resistors may be
separated into two or more series elements if voltage
breakdown and/or regulatory compliance is of concern.
5.1.2 PFC Input Filter Capacitor
For a typical 115 W PFC output stage required to power up a
108 W fluorescent ballast, an input filter capacitance of
0.33 μF is recommended. Capacitor tolerances and the value
of the EMI filter capacitor need to be considered when
selecting the value of the capacitor to be used in this
application.
DS904A7
11