MP4033—PRIMARY-SIDE–CONTROL, OFFLINE LED CONTROLLER WITH PFC

MP4033 Rev. 1.0

www.MonolithicPower.com

17

10/22/2014

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

© 2014 MPS. All Rights Reserved.

Power-Factor Correction

The MULT pin is connected to the tap of a

resistor divider from the rectified instantaneous

line voltage, driving a sinusoidal multiplier output.

This signal provides the reference for the current

comparator, which shapes the primary-peak

current into a sinusoid and has the same phase

with the input line voltage. This guarantees a

high power factor.

Inductor current

Multiplier output

Figure 4: Power-Factor Correction

The multiplier’s maximum output voltage to the

limit the cycle-by-cycle current. The multiplier’s

to ensure a turn-on signal during the TRIAC

dimming OFF interval, which pulls down the

rectifier input voltage and accurately detects the

dimming phase.

VCC Timing Sequence

The VCC timing sequence is shown in Figure5.

Initially, VCC charges through the internal

charging circuit from the AC line. When VCC

charging, the control logic initializes and the

internal main MOSFET begins to switch. The

auxiliary winding takes over the power supply.

However, the initial auxiliary-winding positive

voltage may not be large enough to charge VCC,

causing VCC to drop. Instead, if the VCC voltage

This cycle repeats until the auxiliary winding

voltage is high enough to power VCC.

If any fault occurs during this time, the switching

and the internal charging circuit stop, and VCC

internal re-charge is enabled to auto-restart.

Auto Start

The MP4033 contains an auto starter that starts

timing when the MOSFET turns off. If ZCD fails

will automatically send a turn-on signal to avoid

unnecessary shutdown.

Minimum OFF Time

The MP4033 operates with a variable switching

frequency; the frequency changes with the

instantaneous input line voltage. In order to limit

the maximum frequency and get a good EMI

performance, the MP4033 employs an internal

minimum off time.

Figure 5: VCC Timing Sequence

Leading-Edge Blanking

In order to avoid premature switching-pulse

termination due to the parasitic capacitances

discharging when the MOSFET turns on, an

internal leading-edge-blanking (LEB) time is

introduced on S pin. The current comparator

blocks the input path from S pin during the

blanking time. Figure 6 shows the leading-edge

blanking.

t

Figure 6: Leading-Edge Blanking