ML4835CP MICRO-LINEAR [Micro Linear Corporation], ML4835CP Datasheet - Page 7

• Manufacturer Part Number: ML4835CP
• Description: Compact Fluorescent Electronic Dimming Ballast Controller
• Manufacturer: MICRO-LINEAR [Micro Linear Corporation]

FUNCTIONAL DESCRIPTION
The ML4835 implements a triple frequency operation
scheme: programmable three-frequency sequence for pre-
heat, ignition, and dimming, that extends lamp life,
simplifies lamp network design, and starts lamps at any
dimming level without flashing. This addresses the need
for a high-Q network for starting sequence and low-Q
network for operation, minimizing parasitic losses and
improving overall power efficiency. The values for the
pre-heat, start, operation, and restart can be programmed
or selected (Figure 2).
PFC OUT
CLK
RAMP
FILTER
EMI
PIFBO
PIFB
START AND OPERATION,
3
SET TIME VALUES
FOR PREHEAT,
AND RESTART
–A
PIFBO
Figure 3. ML4835 PFC Controller Section
Figure 2. Three Frequency Design Model
R
L
SENSE
13
4
(Continued)
C
C
RAMP
RAMP
+
–
18
PFC OUT
ML4835
OSC
V
TO
I
SW1
SW2
POWER FACTOR SECTION
The ML4835 power factor section is a peak or average
current sensing boost mode PFC control circuit in which
only voltage loop compensation is needed. It is simpler
than a conventional average current control method. It
consists of a voltage error amplifier, a current sense
amplifier (no compensation is needed), an integrator, a
comparator, and a logic control block. In the boost
topology, power factor correction is achieved by sensing
the output voltage and the current flowing through the
current sense resistor. Duty cycle control is achieved by
comparing the integrated voltage signal of the error
amplifier and the voltage across R
control timing is shown in Figure 3.
2
S
R
HIGH Q
R1
PEAO
START
C1
PEAO
Q
CLK
f 2
C2
–
+
PREHEAT
f 1
LOW Q
RA
RB
VREF1
V
OUT
OPERATION
f 3
INVERTER
PVFB/OVP
1
NETWORK
SENSE
LAMP
. The duty cycle
ML4835
LAMP
LAMP
7