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:

• replacing the fluorescent tubes with with power efficient LED backlighting,

• replacing the switching mode power supply with a clean linear power supply

• shielding the main board.

  Disclaimer: The statements made in this document are based on the experience of an individual who suffers from EHS. The modifications have helped alleviate some, but not all of the ill symptoms from using the monitor..The author is not responsible for any losses which may incur from modifying your monitor.

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

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.