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

MP4056 Rev.1.01

www.MonolithicPower.com

21

11/9/2016

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

© 2016 MPS. All Rights Reserved.

Opto-coupler

Circuit

DIM

Ra

LED String1:

LED String 2:

LED+

LED+

LED-

LED-

Figure 16: Color Temperature and Brightness

Control Circuit

The DIM pin of MP4056 outputs a driving signal

for an external MOSFET. The DIM signal logic

waveforms are shown in Figure 17.

MULT

DIM Signal

30 % Line-cycle

blanking

Turn on cycle

detector output

Figure 17: Dim Signal Logic

DIM turn-on signal is the compliment signal of the

dimming turn-on signal. This means the longer

the dimming turn-on cycle, the smaller the DIM

turn-on cycle. When the dimming turn-on cycle is

greater than 70%, the DIM stays low, and the

string. As the dimming turn-on cycle decreases,

the

DIM

turn-on

duty

cycle

proportionally

stays constant. This current balance achieves

color temperature and brightness control. The

Dimming Depth Enlargement

Driving a MOSFET to pull down a resistor from

auxiliary winding to GND forms a dummy load,

which to help distribute the output current. The

DIM pin working timing makes the smaller

dimming duty cycle is, the bigger dummy load

distribution current is, the dimming depth is

enlarged. The dimming depth enlargement circuit

is shown in figure 18.

VCC

DIM

Figure 18: Dimming Depth Enlargement circuit

Programmable Thermal Fold-back (NTC)

The NTC pin is used as the LED programmable

thermal fold-back. A NTC resistor is connected to

this pin directly to monitor the LED temperature.

The LED current reduces as the voltage drops on

NTC. Figure 19 shows the NTC curve.

Io

Iset/3

0

Iset

Figure 19: NTC Curve

If the voltage on the NTC pin is lower than the

value. The minimum output current is determined

by the minimum on time (LEB time) of the main

MOSFET.

Analog dimming with PWM Input

The MP4056 enables direct control of analog

dimming. Applying a PWM signal (>200Hz) on

NTC achieves analog dimming. The output

current will linearly change with the PWM duty

cycle from maximum to minimum. This feature

dramatically reduces the BOM cost for the PWM

dimming system.