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

MP4033 Rev. 1.0

www.MonolithicPower.com

16

10/22/2014

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

© 2014 MPS. All Rights Reserved.

OPERATION

The MP4033 is a TRIAC-dimmable primary-side–

control, offline LED controller designed for high-

performance

LED

lighting.

The

MP4033

accurately controls the LED current using the

real-current–control method based on primary-

side information. The adaptive dimmer type

detection and phase-cut-based dimming control

bring good dimmer compatibility and deep

dimming range. It also achieves a high power

factor to eliminate noise pollution on the AC line.

The integrated VCC charging circuit achieves

fast start-up without any perceptible delay. The

programmable thermal current fold back function

prolongs the lifetime of the LED. With duty ratio

varies with dimming cycle, the DIM pin easily

supports color temperature and brightness

control for warm sunset dimming application. The

MP4033 is also available for analog dimming with

PWM input.

Boundary-Conduction Mode

rectified input voltage applied on the primary-side

inductor (Lm) makes the primary current thru Lm

then the external MOSFET turns off. The energy

stored in Lm forces the secondary side rectifier

diode to turn on, and the inductor current

decreases linearly from the peak value to zero.

turn on

0

Inductor

current

Figure 2: Boundary-Conduction Mode

When the current decreases to zero, the voltage

drop on the main MOSFET drain-to-source falls

and oscillates. The oscillation frequency is

determined by the primary side inductor and the

combined parasitic capacitances. The resonance

is reflected on the auxiliary winding (see Figure

2).

The zero-current detector generates the external

MOSFET turn-on signal when the ZCD voltage

and ensures the MOSFET turns on at a relatively

low voltage (see Figure 3).

Figure 3: Zero-Current Detector

As a result, there are relatively small primary

switching on losses and no secondary-diode

reverse-recovery losses. This ensures high

efficiency and low EMI noise.

Real-Current Control

The

proprietary

real-current–control

method

allows the MP4033 to control the secondary-side

LED current based on primary-side information.

The approximate output LED mean current can

be calculated as:

⋅

≈

⋅

REF

o

s

NV

I

2R

Where:

• N is the turn ratio of the primary side to the

secondary side,

(typically 0.414), and

MOSFET source and GND.