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
RAC
RFB
R1a
R1b
R1c
R2a
R2b
R2c
BR1
BR1
CS1600
Clink
1
3
7
8
2
4
6
5
C3a
C3b
NC
STBY
C1
AC
Mains
IAC
VDD
NC
FB
GD
+12V
Q1
R3
C2
BR1
BR1
GND
Figure 17. CS1600 Basic Application Circuit
5.1
Component Selection Guidelines
[Eq.5]
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:
RAC = RFB
RAC = 3.45MΩ
where
V
V
108 VAC
305 VAC
460 V
in(min)
RFB = Feedback resistor used to reflect the PFC output
voltage
in(max)
RAC = Feedforward resistor used to reflect the rectified line
voltage
V
link
P
115 W
95%
o
Vlink= PFC Output Voltage
η
V
DD = IC Supply Voltage
I
ref = Target reference current used for feedback
5.1.1 IAC and IFB Sense Resistors
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.
The rectified line voltage, VAC, and the output voltage of the
PFC boost converter, Vlink, are scaled as currents by using
sense resistors, whose values are estimated based on the
equations below:
V
link – Vdd
5.1.2 PFC Input Filter Capacitor
---------------------------
[Eq.4]
RFB
RFB
=
=
Iref
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.
460 – 12
---------------------------
130 × 10–6
RFB = 3.45MΩ
DS904A5
11
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