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

MP4033 Rev. 1.0

www.MonolithicPower.com

19

10/22/2014

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Adaptive Dimmer Type Detection

The MP4033 integrates adaptive dimmer type

detection to accurately detect which kind of

dimmer is connected at the system start-up,

leading edge dimmer, trailing edge dimmer or no

dimmer. The MP4033 works in different modes

depending on these dimmer types to achieve the

best

dimmer compatibility at the highest

performance.

Phase-Cut-Based Dimming Control

The

MP4033

implements

phase-cut-based

dimming control (both for leading edge and

trailing edge dimmers). For the leading edge

dimmer, most of them are TRIAC-based.. The

TRIAC dimmer usually consists of a bi-directional

SCR and an adjustable turn on phase. Figure 10

shows

the

leading-edge

TRIAC

dimmer

waveforms.

Line voltage

after TRIAC

dimmer

Input line

voltage before

TRIAC dimm er

Rectified line

voltage

Dimmer

turn on

phase

Line cycle

Figure 10: Leading Edge Dimmer Waveforms

For the Trailing edge dimmer, the waveforms are

shown in Figure 11.

Figure 11: Trailing Edge Dimmer Waveforms

The MP4033 detects the dimming turn-on cycle

through the MULT pin. Based on the turn-on

cycle, the control circuitry adjusts the internal

reference voltage. MULT voltage exceeding

dimmer turn-off signal. The MP4033 has a 30%

line-cycle-detection blanking time at each line

cycle, the real phase detector output added this

blanking time to determine the reference voltage,

if it is higher than 100%, the reference voltage is

clamped to 100%. As shown in FigureError!

Reference source not found.

12. That means if

the turn-on cycle exceeds 70% of the line cycle,

the reference maintains the maximum value,

which makes the maximum output current with

different dimmers is almost the same with the

rated output current.

Figure12: Dimming Turn-On Cycle Detector

When the turn-on cycle decreases to less than

70% of the line cycle, the internal reference

voltage decreases, lowering the output current.

As the dimming turn-on cycle decreases, the

COMP voltage also decreases. For leading edge

dimmer, once the COMP voltage reaches

decreases slowly to maintain the TRIAC holding

current and avoid random flicker. Figure Error!

Reference source not found.

13 shows the

relationship between the leading edge dimming

turn-on phase and output current.