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Please help me with this LED circuit.

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cadusir

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Hi
First of all I'm a newbie in electronics so please don't get angry with my primitive questions.
Concept:
I want to use LED's as back-light for a LCD monitor.
(Powers is perfect but inverter is gone and parts are not available. they want 65$ for a "used" "repaired" inverter so I decided to do this)
=========================================
I read a lot about back lighting and other things. finally found a probably good circuit diagram for my purpose in a Russian site (used Google translate).
here it is:
MC34063A.jpg
the circuit seem perfect for me but I have to do some modifications:
1. I have to use 60 LED's
2. I want to have the option of dimming the LED's (not logical, a simple potentiometer would be OK).
Now what I want to know:
1. Is it better to make two units for every 30 LED's?
2. this circuit has 41 LED's but I want to use 30 or 60, what should I do? 3 rows of 10 LED's? 4 rows of 15 LED's? or else?
3. I found a website (MC 34063 Step-Up/Down Calculator) that calculates all the values and give the parts, but I'm confused because:
a) It wont give standard values for the parts. (the most important of them for me is L1)
b) I don't know how to configure the LED's so I can't calculate needed voltage and other parameters.
what I have:
1. 14V power source.
2. 60 LED's (SMD-3528) VF 3.2v, If 20mA, Pd 173mW.
3. 5 volts on/off signal to feed the FET for turning on/off the circuit.
OK, I know it's kind of rudeness but the final request would be:
1. LED configuration.
2. part values.
Any suggestions would be appreciated even referring me to further reading would be OK.
Thank you
 
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tpetar

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cadusir

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Thanks tpetar.
Check this:

Conversion of LCD Monitor to LED
LCD Backlight Conversion to LED
I already saw that before.
I think it's kind a strange and dangerous to do this.
I'm using smd LED's so I can put them inside the ccfl holder instead of drilling them :)
That was helpful.
Actually I do have that type of flexible LED strings but the LED's are too faraway from each other so I decided to remove them and again soldier them in smaller package.
Look this circuit solutions:
LED Backlight Driver For Medium/Large Displays
https://circuits.datasheetdir.com/58/A8512-circuits.jpg

6-Channel Current Regulator For LED Backlight Application
https://circuits.datasheetdir.com/58/LM3432-circuits.jpg
Circuits are great but I'n not sure if I can find A8512.
Tomorrow I'll go to electronic stores and ask for them.
Unfortunately I can't buy from internet stores.
Thank you it was very helpful.
Best Regards
 

cadusir

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Dont worry I will send You simpler circuit with some user friendly uC or just IC. :wink:
Thanks.
Actually this circuit with LM3432 seems perfect, today I'm going to find out if it's available in local stores.
And something funny...
I tried the method in that youtube video, can't believe it because it's really working but there is some problems. there is no control over the back light and it's always turned on. to turn it off I have to unplug the main power cable.
I tried to find a start circuit or kind of control circuit between the power section and inverter section but unfortunately 14v line goes directly to FET and HVT.
So dear tpetar I'm still searching for the good circuit and rely upon no one but three; you, google and ***! :lol:

P.S. what about this (***)?
Hey they censored him!
I should know that our erathtly science doesn't have anything in common with the almighty :wink:
 
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tpetar

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there is no control over the back light and it's always turned on. to turn it off I have to unplug the main power cable.

You can add optocoupler on power in monitor when present turn LED on or off.
You can sense direct hight voltage or some lower in monitor.
My suggestion is to find some low voltage in monitor and sense him with optocoupler.

Look this for 220V its simple :
c_507_phonecontroller_sens_pic.jpg
 
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cadusir

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OK, no LED controlling IC for me!
I listed 15 different types but none of them available here.
So it seems that I have to stick to the 12v LED string and that optocoupler or some simple transistor circuit.
tpetar I want to thank you for your help and sharing your knowledge with me.
Best regards
 

tpetar

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Dont worry I will help You.

---------- Post added at 21:18 ---------- Previous post was at 20:13 ----------

I suggest You that for switch use optocoupler with some mosfet as switch (turn On when sense current in monitor).

Look this circuit examples may be useful:
Web location :
Led drivers | Electronics Projects , Electronic Circuits Diagrams and Schematics
**broken link removed**

**broken link removed****broken link removed****broken link removed****broken link removed**

Also You can always make easy circuits (ok 3 in line, but consider usage of voltage boosters):
Build a Mechanical TV Monitor, Part 2

Schematics of delabs: Constant Current Source LED Drive
**broken link removed**

MAX6969
MAX6969 16-Port, 5.5V Constant-Current LED Driver - Overview
**broken link removed**


4809.gifcurrent-source.pngISL97672A-led-driver.jpgLNK407EG-15W-LED-driver-circuit.jpgLT3746-32-channel-led-driver.jpgltc_fig_2.jpg


LM3530 white LED driver circuit design
LM3530 white LED driver circuit design electronic project
LM3530-led-driver.jpg

ISL97671
6-Ch 45V/40mA per ch LED Driver
Display Power - Power Management
isl97671_block.jpg

See this than we continue...
 
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cadusir

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Oh tpetar I don't know how to thank you.
one more thank for the invitation to the group.:grin:
I'll start reading right now!
 

tpetar

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See this simple:

The circuit below can be modified to drive up to 30 white LEDs.
The effectiveness of a LED array increases when they are spread out slightly and this makes them more efficient than a single 1 watt or 2 watt LED. The two modifications to the circuit make the BC337 work harder and this is the limit of the inductor. The current consumption is about 95mA.

LED.gif
 

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