MP4700 – HIGH-BRIGHTNESS BCM, LOW SIDE BUCK WLED DRIVE WLED DRIVER

MP4700 Rev. 1.0

www.MonolithicPower.com

12

10/29/2012

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© 2012 MPS. All Rights Reserved.

DESIGN EXAMPLE

TV LED Backlighting

The design example introduces an MP4700-

based high-performance TV LED backlighting

solution. Figure 2 shows the structure of this

total system solution—Flyback+MP4700 low-

side buck for single-string TV LED backlight.

The flyback converts the AC input line voltage

to the system output supply voltage 13V/2A,

and also outputs a DC bus voltage (around

280V) to the LED driver. The flyback is based

on the MPS quasi-resonant flyback controller,

HFC0100. The MP4700 acts as the LED driver

stage as a boundary conduction mode (BCM)

low-side buck.

Figure 2: Power System Structure

Specifications:

Description

Parameter

Units

Input voltage

110 to 265

VAC

Input frequency

50

Hz

Output DC Bus voltage

13.4

V

Output DC Bus current

2

A

LED Voltage

210

V

LED Current

250

mA

Protection: short LED protection, open LED

protection and 13V over-voltage protection.

Schematics:

Figure 3 and Figure 4 show the schematics of

the HFC0100 flyback stage and the MP4700

LED driver stage. The parameters of the power

transformer T2 are as follow:

Turn ratio:

In this application example, the bus voltage

uses 2 windings. Each winding outputs half of

the bus voltage (140V) after the rectifier,

dividing the voltage stress across each rectifier

diode. The reduced stress allows for the use of

800V diodes.

Both the 13V voltage and the 280V bus voltage

feed back to the flyback control circuit, which

decreases the influence of the cross regulation.

The 13V system voltage also supplies the

MP4700.

The following describes the design of the

MP4700 LED driver. The design procedure for

the HFC0100 flyback is not described here, but

rather in the HFC0100 design materials.