LCD Monitor with LED Backlighting and Linear Power Supply Tutorial



by Eli, www.ahappyhabitat.com



Purpose

Today's electronic devices are making people ill and impairing them with an ailment called Electromagnetic Hypersensitivity (EHS). The impairment can become so severe such that using a computer is too painful. It is the goal of this tutorial to describe how to modify a standard LCD monitor to make it more tolerable. Primary modifications include:





Overview










Main Components of the Monitor

  1. LCD monitor

  2. Remote linear power supply in shielded case

  3. Power supply extension cable

  4. Connector for power supply extension cable

  5. Shielded AC cord for the remote power supply



This picture shows the main components of the LCD monitor. At the rear of the monitor is the connection receptacle for the remote power supply. Note that the “IP board” or switching power supply has been gutted from the chassis of the monitor and replaced with the remote power supply. The AC power chord no longer connects directly to the monitor, but rather connects to the remote power supply. The components include:


    Parts List



Description

MFR Part #

Vendor Part #

Quantity

LCD Monitor

Samsung 731BF


1

LEDs

Lumileds Lighting

LXHL-PW09

Future Electronics, inc

8

Heat Sink

HS374-ND

Digi-Key NZ-5533

2

Silicon Grease

CT40-5-ND

Digi-Key NZ-263

1

Crimp Pin Contact (Male)

02-06-2103 (Molex)

NewarkInOne 35C4909

1

Crimp Socket Contact (Female)

02-06-1103 (Molex)

NewarkInOne 35C4908

1

12 Contact Connector -(Female)

19-09-1126 (Molex)

NewarkInOne 83C8069

2

12 Contact Connector (Male)

19-09-2126 (Molex)

NewarkInone 22C6724

2

Bridge Rectifier

International Rectifier

KBPC6005

NewarkInone 06F8797

2

Voltage Regulator

National Semiconductor

LM338T

NewarkInone 07B6484

2

PCB Prototyping Board

Vector Electronics

8015-1


2

Toroidal Power Transformer 50VA

Hammond 182N6

NewarkInone 95B5026

1 or 2

Or

Transformer Kit


www.Toroid.com

1 or 2

Hook-up wire (AWG 18)

Dearborn 171819-100-9

NewarkInone 03F4432

1 (100 ft)

Hook-up wire (AWG 20)




Electrolytic Capacitor (4700 uF)

Multicomp MCHT472MICB-1633-RH

NewarkInone 79K3628

6

Electrolytic Capacitor (47uF)

CDE Mallory SKA470M035

NewarkInOne 16F2302

2

AC Power Cable

Radio Shack



LCD Monitor Service Manual (731BF, 931BF)


www.justmanuals.com


Mu metal (0.006” thick – 15” x ?)


Ad-Vance Magnetics, Inc

AD-MU-80 Foil


Resistor (1.8 Ohm)

5073NW1R800J

NewarkInOne 94C2294

1

Resistors (½ Watts – 120, 330, 39 ohm)
























Installing LEDs















































LEDs Installed in Upper Part of Monitor

  1. 20 AWG wire

  2. LEDs

    After the fluorescent tubes are removed, the LEDs can be added. A total of 8 LEDs are installed, 4 on top, 4 on the bottom. The above picture shows the top 4 LEDs. The LEDs are all wired in parallel. Each is glued to the metal chassis of the monitor. The metal chassis serves two purposes; to hold the LEDs securely in place, and to serve as a heat sink. The LEDs are simply glued to the chassis with crazy glue.





























LED Schematic

Power Supply















































Expanded View of the Power Supplies.

  1. Mu metal case

  2. Toroid Transformer

  3. 5 volt LCD power supply

  4. 700 mA LED power supply

  5. 12 volt fan

  6. AC Power chord

  7. 12 volt cable for fan

  8. 18 ft cable from power supply to monitor



The power supply comprises a linear 5 volt regulated supply to power the main board of the LCD, and a 700 milli amp linear current regulated supply for the LEDs. A single toroidal transformer has two secondary windings, one for each power supply. If one is willing to pay the extra price, two independent 50 VA transformers was found to reduce the emitted magnetic field. An external 12 volt linear power supply is used to power the fan.



Each power supply is wrapped in a few layers of 0.006” mu metal foil to reduce the magnetic field. The transformer is placed on a towel to keep it centered in the mu metal case. Don't let the transformer come in contact with the shielding – keep some distance. The case is made of 0.06” thick mu metal shielding which was bought in bulk quantities at a hefty cost. One may want to use the 0.006” and wrap it into a few layers. The heavier the shielding, the less emitted magnetic field.













































    Close up View of LED power supply

  1. Rectifier

  2. Capacitor (power conditioning)

  3. Linear Voltage Regulator attached to heat sink

  4. Resistor

  5. Capacitor (output stabilization)

  6. PCB Prototyping Board



The electronic components are soldered into a PCB prototyping board. Connections are made with 18 AWG wire.





































    Schematic LCD 5 Volt Power Supply

    1. T1 – 50 VA Toroidal Power Transformer

    2. R1 – Rectifier

    3. C1 – 4700 uF Capacitor

    4. C2 – 4700 uF Capacitor

    5. C3 – 4700 uF Capacitor

    6. C4 – 47 uF Capacitor

    7. R1 – 120 Ohm

    8. R2 – 369 Ohm (39 + 330)





































Schematic LED 700 mA Current Regulated Power Supply

  1. T1 – Toroidal Power Transformers

  2. R1 – Rectifier

  3. C1 – 4700 uF Capacitor

  4. C2 – 4700 uF Capacitor

  5. C3 – 4700 uF Capacitor

  6. C4 – 47 uF Capacitor

  7. R1 – 1.8 Ohm

    .

Making the Power Cable

















































Insulated Power Cable

  1. Aluminum Foil

  2. 18 AWG Wire

  3. Bare, grounded wire



Insulated, multi-core cables are very expensive so it pays to take the time to make one yourself. Lay the wires out (18 ft in this case), including a bare (uninsulated) wire which is used to ground the aluminum shield. The grounded wire is then connected to a ground source. Add the Molex connectors to both ends.



Monitor Main Board Power Supply Filter






This filter goes between the DC linear power supply and the monitor. It's placed as close to the monitor controller board as possible. It's vital function is to prevent noise emitted from the LCD main board from being conducted onto the power cable. This filter reduces the 60 Hz and 30 kHz noise.