MP4056—TRIAC DIMMABLE, NON-ISOLATED OFFLINE LED CONTROLLER WITH APFC

MP4056 Rev.1.01

www.MonolithicPower.com

19

11/9/2016

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

© 2016 MPS. All Rights Reserved.

Thermal Shutdown

To prevent IC from thermal damage, the MP4056

latches off the switching cycle when the junction

temperature is higher than 150°C. When the

VCC drops below UVLO, it restarts again.

Adaptive Dimmer Type Detection

The MP4056 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 MP4056 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

MP4056

implements

phase-cut-based

dimming control (both for leading edge and

trailing edge dimmers). For

leading edge

dimmers, 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 dimmer

Rectified line

voltage

Dimmer

turn on

phase

Line cycle

Figure 10: Leading Edge Dimmer Waveforms

For trailing edge dimmers, the waveforms are

shown in Figure 11.

Dimmer turn

on Phase

Line Cycle

Input line

voltage

before TRIAC

dimmer

Input line

voltage after

TRIAC

dimmer

Rectified

line voltage

Figure 11: Trailing Edge Dimmer Waveforms

MP4056 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. MP4056 has a 30% line-

cycle-detection blanking time at each line cycle.

The real phase detector output adds this blanking

time to determine the reference voltage, if it is

higher than 100%, the reference voltage is

clamped to 100%, as shown in Figure 12. This

means if the turn-on cycle exceeds 70% of the

line cycle, the reference maintains the maximum

current value, which keeps the maximum output

current with different dimmers is almost the same

with the rated output current.

MULT

Comparator

Output

30% line cycle

blanking

Turn on cycle

detector output

Figure 12: Dimming Turn-On Cycle Detector

When the turn-on cycle decreases to less than

70%, the internal reference voltage decreases,

lowers the output current. As the dimming turn-on

cycle

decreases,

the

COMP

voltage

also

decreases. For leading edge dimmers, once the

The output current decreases slowly to maintain

the TRIAC holding current and avoid random

flicker. Figure 13 shows the relationship between

the leading edge dimming turn-on phase and

output current.