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

MP4026 Rev. 1.1

www.MonolithicPower.com

15

9/9/2015

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

© 2015 MPS. All Rights Reserved.

On the other hand, the non-dimmable solution

usually needs to cover universal input range.

The input range is very wide, from 85VAC to

264VAC. The MULT pin is used to detect the

input voltage signal, but the resistor divider of

MULT is fixed. So, at high line input, the signal

for MULT input is very low, which results in

adverse effect for internal multiplier sampling,

then affect the PFC performance.

Figure 12 shows an improved circuitry on MULT

resistor divider to adjust the ratio of the divider

to achieve better THD.

MULT

Multiplier

COMP

BUS

ZD1

Figure 12: THD Improved Circuitry

The ZD1 is a HV Zener diode. The common

voltage rating is from 80V to 130V.

At low line input, the BUS can not breaks down

ZD1, the MULT pin signal is

=×

+

MULT2

MULT

BUS

MULT1

MULT2

R

VV

RR

When the input voltage rises up, once the BUS

raise the MULT signal.

Figure 13: The MULT Signal with THD Improved

Circuitry

As Figure 13 shown, after adding the THD

improved circuitry, the top part of the MULT

voltage rises up as the dashed line. Then the

input current at top of BUS is increased while

the input current at the zero-crossing is reduced,

which results in the input current more like

sinusoid and then the THD is improved.