MP4652—HIGH PERFORMANCE OFF-LINE TV LED DRIVER

MP4652 Rev. 1.01

www.MonolithicPower.com

14

9/23/2011

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© 2011 MPS. All Rights Reserved.

EXAMPLE APPLICATION

TV LED Backlight

This application example introduces a high

performance 2-stage LLC TV LED driver that is

designed to power the LED backlights for a 40-

inch TV. The total system power structure is

shown in Figure 6. It uses a 2-stage structure

with high efficiency and low cost. The PFC stage

outputs around 390V and is controlled by the

MPS PFC controller MP44010, which works in

BCM (Boundary Conduction Mode). The MP4652

acts as the LED driver stage: it controls a LLC

power stage to drive the LED strings. Another

flyback DC/DC stage outputs the 13V power

supply for the system: it uses the MPS quasi-

resonant flyback controller HFC0100.

PFC stage

MP44010

AC

input

LED Driver stage

MP4652 LLC

.

.

.

LED strings

Flyback DC/DC

HFC0100

13V/3A

PFC_390V

.

.

.

Figure 6—System Power Structure

The following introduces the detailed circuit of the

LED driver stage based on MP4652. The

specifications for this LED driver are listed below.

Specification:

Input: typically 390V, PFC Output.

Output: 4 strings at 55V/260mA per string,

connecting 2 strings in series. It could also output

2 strings at 110V/260mA per string.

Operating frequency: ~110kHz

PWM dimming frequency: 320Hz

Protection: Open LED protection, short LED

string protection, short LED+ to GND protection

Schematics:

Figure 7 shows the schematic of the LED driver

stage. The parameters of the power transformer

T2 are as follow:

NP: NS = 65:35, Leakage inductance = 450μH,

magnetic inductance = 1.6mH.