How could I install a new 12 volt backlight?

Okay, first of all you cannot just solder in a voltage regulator directly to your 80 volt output is just going to blow your new backlight. First things first we need to get some information about your new backlight, and your tv. Specifically what is the current rating of the light, and what is the current output of the TV power supply driver?

While hooking up a voltage regulator will change the output voltage it will not limit the current. This will be just like hooking up and led up directly to a battery. Once you have the current output and the current rating we can design a circuit that will limit the current, and drop the voltage, the circuit will most likely integrate a voltage regulator. You also probably need a couple of half watt or 1 watt resistors dropping from 80 volts down to 12 volts will cause a high rate of power dissipation, and since your television will be running for extended periods of time, you will want to make the circuit as close to indestructible as possible. Also keep in mind that the voltage regulator dropping from 80 down to 12 volts is also going to be dissipating a great deal of heat, you're going to have to have a heat sink attached to it and that will take up a bit of space, and you don't want that touching any of the plastic parts of the television.

Please post the following information:

Backlight power dissipation, and current rating.

Television monitor driver current output.

You should be able to find all this in the data sheet for the light bar, might have to do some digging to get the information about the television driver output. If you can't find the information for the television we can still probably design the circuit by assuming that the television current source will attempt to supply infinite current, it would just be nice to have that information handy.

Well, here's the problem. The backlight I purchased had literally no documentation attached. It's a cheap one from China. All I know is that the LED driver that it shipped with runs on 12 volts at least, and it needs an enable signal. I am very hesitant to attach my multimeter to read the current draw of it, as my multimeter has a 10 amp capacity and has no fuse (the milliamp setting is also unfused since the original fuse blew and I just decided to bypass it)

What I meant about tying a regulator to the 80v output, I meant attaching the new driver to that with the 12v regulator or something. The LED driver would then limit the current if I am not mistaken, since it ran just fine from the PC power supply. If I can grab power from somewhere else on the power board that turns off when it goes into sleep mode, then that would be great. The enable line on the LED driver can take as little as 5v (based on what I used on the PC power supply) to turn on, so that can be separate.

As for the calibration and whatnot, I don't really think that's necessary, because I ran the panel with the new backlight in there and I was very satisfied with the results. It works, but now I'm just looking for a way to run it as just the monitor, not a string of parts everywhere.

I will do some research on the monitor. It is an ASUS VK248. What I do know is that the power going to the logic is just 5v.

In my opinion, there appears to be plenty of space for a heat sink to fit within the metal shielding of the device. Here's some pictures to maybe give you guys a better idea. https://drive.google.com/folderview?id=0B5FOtrrp9MnYZDMwcHI1TUJxOUU&usp=sharing

Here is an idea of what you are doing.

Are you sure your led/diode is connected the correct way?

Just a thought.

P.S. I know the ground is connected, I just forgot to add that to the diagram.

Also, Please take Voltage readings for ground, and each "LEG" of the circuit, This will be most helpful.

I.E. reading at pin 2, than at pin3, resistor, then at diode/Led, both sides, etc.

Your power supply is on? right? No short connections ? right? No wrong opto-coupler connections? No blown opcto-coupler?

Good thinking, Hopefully If he posts the voltages on the circuit, this can be answered.

mudz wrote:

 

Your power supply is on? right? No short connections ? right?

supper_slash

Great circuit but the Base of the transistor remains unconnected.

ie Pin 6 is either unconnected or in some case tied to Pin 4 via a 1Mohm resistor.

Mark

Yes, my power supply turns on, and yes, the LED turns on.

I have jotted down a crude schematic of what I currently have connected. This is the FOD3184 chip. One interesting thing I noted here is that operating the LED generated slight negative voltage on the ground of one side, but not the other. There was no voltage being output by the sensor side of the coupler at all, as when I disconnected it, I got 0 on the output.

Here's my schematic with my voltage and amperage readings, and the link to the full-resolution

http://puu.sh/mMi2D/d4665b25e5.jpg

supper_slash is right. Remove all the connections first and check if opto coupler is working fine by giving input and checking out on Vo using multi meter. Most of the times when the circuit is not working I found that a floating ground pin was the fault. so carefully connect all ground connections.
On the second thought: Hey, look what I found:-

So you need to apply more voltage on VDD to turn the Vo pin high. Apply at least 13.5v-14v on VDD pin.
Hope this helps.

mudz

bwarren97

Clearly some comments are missing the point.

You have a 1.47v drop across the LED, which is within spec.

The second LED has a 2.98v drop across it (3.53-0.55 = 2.98).

This is resulting in the forward current being 5.5mA

(0.55v across 100ohms is .0055A).

The specs show you need 10-16mA

I suggest either find a lower forward voltage led or remove it and increase the series resistor back up to 220 ohms.

This optocoupler has a high output current and noise immunity, hence the fairly high input requirements.

Mark

bwarren97

BTW you are looking for 1-1.6v acrss the 100 ohm resistor if you change the LED.

Generally the higher output/brighter LED's require a higher forward voltage, so look for some lowly old red LED.

Mark

So, this was starting to make a lot more sense to me. However, I tried both switching the LED and removing it altogether. Still nothing

I got a reading of just over 10mA using the lower power LED, and got a reading of about 14mA when I removed it and increased the resistor. The output on the optocoupler remained 0.

Hi bwarren97
If you move to post number 30 (i.e. first post in this page & leave first two lines), you'll know why you are not getting a high on output (Vo pin)
It's because you are not applying enough voltage on the Vdd pin, use minimum of 13.5v.

mudz

Hi bwarren97
If you move to post number 30 (i.e. first post in this page & leave first two lines), you'll know why you are not getting a high on output (Vo pin)
It's because you are not applying enough voltage on the Vdd pin, use minimum of 13.5v.

mudz

So @mudz Do you think @Blake Warren can power the circuit from the 14-volt rail of the power circuit?

Or just replace the Opto to a lower level one?

What are you thinking?

I feel like a different Opto is in order.