MP4026 – PRIMARY SIDE CONTROL, OFFLINE LED CONTROLLER WITH ACTIVE PFC

MP4026 Rev. 1.1

www.MonolithicPower.com

10

9/9/2015

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© 2015 MPS. All Rights Reserved.

OPERATION

The MP4026 is a primary-side-controlled, offline

LED controller for high-performance LED

lighting. It has primary-side real-current control

for accurate LED current regulation. It also has

active power factor correction (PFC) to

eliminate harmonic noise on the AC line. The

rich protections can achieve a high safety and

reliability in real application.

Start Up

control logic starts. Then the power supply is

taken over by the auxiliary winding when the

voltage of auxiliary winding builds up.

below 9.3V.

The high hysteretic voltage allows for a small

VCC capacitor (typically 4.7μF) to shorten the

start-up time.

Valley Switching Mode

the energy stored in the inductor is transferred

to the secondary-side, which activates the

secondary-side diode to power the load. The

its peak value to zero. When the secondary

current decreases to zero, the MOSFET drain-

source voltage starts oscillating, which is

caused

by

the

primary-side

magnetizing

inductance and parasitic capacitances—the

voltage ring also is reflected on the auxiliary

winding (see Figure 2). To improve primary-

control precision, the chip monitors when ZCD

voltage falls to zero twice before the next

switching period. The zero-current detector

from CS/ZCD generates GATE turn-on signal

when the ZCD voltage falls below 0.295V the

second time (see Figure 3).

This virtually eliminates switch turn-on loss and

diode reverse-recovery losses, ensuring high

efficiency and low EMI noise.

0

Magnetizing

Current

Turn On

Figure 2: Valley Switching Mode

Figure 3: Zero-Current Detector

Real-Current Control

The proprietary real-current-control method

allows the MP4026 to control the secondary-

side LED current using primary-side information.

The mean output LED current is approximately:

FB

o

s

NV

I

2R

⋅

≈

⋅

Where:

• N is the primary-side-to-secondary-side turn

ratio,

(typically 0.413V), and

between the MOSFET source and GND.