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| Powering an LED backlight http://forum.lcdinfo.com/viewtopic.php?f=6&t=2167 |
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| Author: | djmonte [ Mon Mar 12, 2007 18:17 ] |
| Post subject: | Powering an LED backlight |
Hi, i have sucessfully replaced an old 240x64 LCD display with a much newer one. i can read the display and the contrast works fine. the next hurdle to overcome is powering the backlight. the old LCD had an EL backlight that was powered from an AC power supply. when i test the power supply it reads 83 volts AC. the new LCD requires 5 volts DC for power. can anyone shed some light on how i would be able to alter the power source to get the 5 volts DC i need. i am not very experienced in electronics but have a basic knowledge and can follow directions very well. Some thoughts i had based on pure speculation: can i take the output of the current AC power supply to power a new DC power supply? should i somehow cut into the current power supply before the inverter to get the DC power i need. again, i have no idea how to accomplish what i'm trying to do, so any info anyone can give me is greatly appreciated. i have the schematics of the current power supply if that will help. thanks nick |
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| Author: | mentallysilent [ Wed Mar 14, 2007 22:06 ] |
| Post subject: | |
if you have an old computer PSU sitting around, just hook up its ground and +5 terminals to a suitable 5 volt voltage regulator. (left most pin = +Vcc, middle = Ground, right most pin = regulated output voltage you feed your LCD with, all of this is of course looking at the voltage regulator when you would want to read the fine print on the package). |
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| Author: | cex [ Thu Mar 15, 2007 18:03 ] |
| Post subject: | Just take off the inverter |
Hello, I think that your old LCD used an electroluminicent sheet or perhaps a CCFL lamp. These devices need AC voltage source. Usually they are powered by a little module called inverter which is connected to the LCD using different wires than the data signals. If the LCD interface logic uses 5V it is very probable that the inverter input was also 5V, so you can take the inverter out of your device and take the 5V to your new LCD. Please note that if your new LCD uses LED diodes is very probable that you need to supply the LEDS via a current limiting resistor to avoid burning the backlight. First of all I'd try to locate the inverted and measure the input voltage with a voltmeter (I suppose you have one, if not, then buy one. Are some models very cheap and you will find it very useful). Hope this helps. Cex. |
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| Author: | djmonte [ Wed Mar 21, 2007 22:26 ] |
| Post subject: | thanks cex! |
worked like a charm. the main power feed to the inverter AC section was +5 volts. i simply removed the first resistor which cut the power to the inverter section. then i had a fresh 5 volt power source for my new backlight. nick |
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