ML4835CS datasheet(7/17 Pages) MICRO-LINEAR

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ML4835

Figure 3. ML4835 PFC Controller Section

FUNCTIONAL DESCRIPTION (Continued)

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).

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 RSENSE. The duty cycle

control timing is shown in Figure 3.

–

LAMP

NETWORK

INVERTER

LAMP

SW2

SW1

RSENSE

VOUT

EMI

FILTER

PIFB

PIFBO

CRAMP

PFC OUT

PVFB/OVP

–A

VREF1

OSC

PIFBO

RAMP

CLK

PFC OUT

CLK

V TO I

PEAO

START

HIGH Q

LOW Q

OPERATION

PREHEAT

ML4835

SET TIME VALUES

FOR PREHEAT,

START AND OPERATION,

AND RESTART

Figure 2. Three Frequency Design Model

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