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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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LCD LED backlight question
Hi,
I just installed this LCD: http://www.mouser.com/catalog/specsheets/M16327UYT.pdf to replace the dead one in an Alesis QuadraVerb (this doesn't really matter, it's more of a generic question). The LCD display itself work fine but to get power to the backlight I ran the 5V source and ground that supplies the LCD part to the LED blacklight and it works too. However I'm wondering if I need to add a resistor to limit the current to the backlight like I normally would with regular 5mm LED. I've read the specs on the backlight but they aren't given as simply as: # 30mA (max) # Typical Voltage is 2.0, with a maximum voltage of 2.8V like I'm used to. Can anyone point me in the correct direction? Thanks! Reply » |
#2
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LCD LED backlight question
"stoneattic" wrote in message
oups.com See page 11 of the spec sheet. VF(typ) = 4.1V @ IF = 112ma. So you will need a series resistor sized to drop .9V at 112ma. -- James T. White |
#3
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LCD LED backlight question
James T. White wrote: "stoneattic" wrote in message oups.com See page 11 of the spec sheet. VF(typ) = 4.1V @ IF = 112ma. So you will need a series resistor sized to drop .9V at 112ma. -- James T. White Thanks! That's actually what I thought but I wasn't sure I was reading that correctly on the spec sheet. So an 8 ohm resistor is the way to go? I assume a 1/4w would be fine? Thanks again |
#4
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LCD LED backlight question
stoneattic wrote:
James T. White wrote: "stoneattic" wrote in message groups.com See page 11 of the spec sheet. VF(typ) = 4.1V @ IF = 112ma. So you will need a series resistor sized to drop .9V at 112ma. -- James T. White Thanks! That's actually what I thought but I wasn't sure I was reading that correctly on the spec sheet. So an 8 ohm resistor is the way to go? I assume a 1/4w would be fine? Thanks again In a pinch you can start with a 500 ohm or so pot, then set it to max resistance, measure the current with a DMM and adjust the pot to get the desired current/brightness and then disconnect the pot, measure the resistance of that and choose a fixed resistor as close as you can get. 1/4W should be plenty, 1/8W should work too. |
#5
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LCD LED backlight question
James Sweet wrote: stoneattic wrote: James T. White wrote: "stoneattic" wrote in message groups.com See page 11 of the spec sheet. VF(typ) = 4.1V @ IF = 112ma. So you will need a series resistor sized to drop .9V at 112ma. -- James T. White Thanks! That's actually what I thought but I wasn't sure I was reading that correctly on the spec sheet. So an 8 ohm resistor is the way to go? I assume a 1/4w would be fine? Thanks again In a pinch you can start with a 500 ohm or so pot, then set it to max resistance, measure the current with a DMM and adjust the pot to get the desired current/brightness and then disconnect the pot, measure the resistance of that and choose a fixed resistor as close as you can get. 1/4W should be plenty, 1/8W should work too. Since I use this thing in the dark mostly I would lean towards the brightest I could get out of it which would be at a resistance of 0. hehe Obviously that's not a good idea. Do you think the 8 ohms would give me the best brightness and still protect the LED enough? I've got 10ohms resistors (1/8 and 1/4W) laying around so I may toss one of those in and call it done. How does that sound? Thanks again! |
#6
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LCD LED backlight question
You don't need it at its brightest if you use it in the
dark. stoneattic wrote: Since I use this thing in the dark mostly I would lean towards the brightest I could get out of it which would be at a resistance of 0. hehe Obviously that's not a good idea. Do you think the 8 ohms would give me the best brightness and still protect the LED enough? I've got 10ohms resistors (1/8 and 1/4W) laying around so I may toss one of those in and call it done. How does that sound? Thanks again! |
#7
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LCD LED backlight question
Since I use this thing in the dark mostly I would lean towards the brightest I could get out of it which would be at a resistance of 0. hehe Obviously that's not a good idea. Do you think the 8 ohms would give me the best brightness and still protect the LED enough? I've got 10ohms resistors (1/8 and 1/4W) laying around so I may toss one of those in and call it done. How does that sound? Thanks again! Measure the current, don't exceed 20mA or the LED will not last long. |
#8
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LCD LED backlight question
James Sweet wrote: Since I use this thing in the dark mostly I would lean towards the brightest I could get out of it which would be at a resistance of 0. hehe Obviously that's not a good idea. Do you think the 8 ohms would give me the best brightness and still protect the LED enough? I've got 10ohms resistors (1/8 and 1/4W) laying around so I may toss one of those in and call it done. How does that sound? Thanks again! Measure the current, don't exceed 20mA or the LED will not last long. Don't I want (nominally) 112mA? |
#9
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LCD LED backlight question
stoneattic wrote: James Sweet wrote: Since I use this thing in the dark mostly I would lean towards the brightest I could get out of it which would be at a resistance of 0. hehe Obviously that's not a good idea. Do you think the 8 ohms would give me the best brightness and still protect the LED enough? I've got 10ohms resistors (1/8 and 1/4W) laying around so I may toss one of those in and call it done. How does that sound? Thanks again! Measure the current, don't exceed 20mA or the LED will not last long. Don't I want (nominally) 112mA? I put a 10 ohm resistor in and get 90mA on the ammeter. Nice bright backlight too. |
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