MP4030—PRIMARY-SIDE-CONTROL, OFFLINE LED CONTROLLER WITH PFC

MP4030 Rev.1.02

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15

4/16/2013

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OCP

signal

0.9V

Latch

ZCD

Gate

RS

R1

R2

LEB

Figure 10: ZCD Over-Current Protection Circuit

Thermal Shutdown

To prevent internal temperatures from exceeding

150°C and causing lethal thermal damage, the

MP4030 shuts down the switching cycle and

restarts again.

TRIAC-Based Dimming Control

The MP4030 can implement TRIAC-based

dimming. The TRIAC dimmer usually consists of

a bi-directional SCR with an adjustable turn-on

phase. Figure 11 shows the leading-edge TRIAC

dimmer waveforms.

Line voltage

after TRIAC

dimmer

Input line

voltage before

TRIAC dim mer

Rectified line

voltage

Dimm er

turn on

phase

Line cycle

Figure 11: TRIAC Dimmer Waveforms

The MP4030 detects the dimming turn-on cycle

through the MULT pin, which is fed into the

control loop to adjust the internal reference

voltage. When the MULT voltage exceeds 0.35V,

the device treats this signal as a dimmer turn-on

signal. When the MULT voltage falls below 0.15V,

the system treats this as a dimmer turn-off signal.

The MP4030 has a 25% line-cycle–detection

blanking time with each line cycle, The real

phase detector output adds this time, as shown

in Figure 12. That means if the turn-on cycle

exceeds 75% of the line cycle, the output

remains at the same maximum current. It

improves the line regulation during the maximum

TRIAC turn-on cycle or without a dimmer.

Figure 12: Dimming Turn-On Cycle Detector

If the turn-on cycle decreases to less than 75% of

the line cycle, the internal reference voltage

decreases as the dimming turn-on phase

decreasing, and the output current decreases

accordingly to implement dimming. As the

dimming turn-on cycle decreases, the COMP

voltage also decreases. Once the COMP voltage

reaches to 1.9V, it is clamped so that the output

current decreases slowly to maintain the TRIAC

holding current and avoid random flicker. Figure

13 shows the relationship between the dimming

turn-on phase and output current.