Use stripped TV as light/backlit sign. Ballast?

[JDC]

I have an LG 39LN5300 that I was using as a backlit sign (no panel, proper pins jumped to power on and light the LEDS, main board removed and sold). Long story short (get it?), the board died.

According to my LED tester (http://www.shopjimmy.com/sid-gj2c-le...ght-tester.htm), I need 100V to light it up. What can I use in place of a power board to do this?

[dick_barton]

Re: Use stripped TV as light/backlit sign. Ballast?

See if any of these are any good. https://tinyurl.com/y8tqgfzj

[Andrew F. Ali]

Re: Use stripped TV as light/backlit sign. Ballast?

I like these and am wondering.....If I'm not getting BL-ON signal from the Main Bd, and everything else works, if I could use with the corrector close enough voltage/current output in a LED TV. I could probably wire the PS-ON signal to close the contacts on a relay to supply this wit 120Vac?

[freakaftr8]

Re: Use stripped TV as light/backlit sign. Ballast?

I stripped down a 60 inch Vizio that had a cracked screen and stripped the power supply out leaving the LED strips and used one of those LED bulbs you get at the store as the supply voltage. I stripped out the led's out of the bulb and wired its transformer directly into the LED strips. I just rewired all the LED strips in parallel. Works great!

The LED light bulb outputs 24v. The LED strips have 11 LEDs across which worked out to 2.18vdc. Well in spec for operating voltage for the LEDs on the strips.

[JDC]

Re: Use stripped TV as light/backlit sign. Ballast?

See if any of these are any good. https://tinyurl.com/y8tqgfzj

They could be but I wouldn't know which one to choose, I'm sad to say.

[budm]

Re: Use stripped TV as light/backlit sign. Ballast?

Can we see the pictures of your power supply/LED driver board top and bottom side and the LED connector to see how many LED strings it has and how the strings are connected together?
The power supply has to be able to supply enough Vf (Forward bias Voltage) for the LED string and then you can pick the power supply with the required Voltage and current for the LED, I would suggest not to drive the LED with more than 300mA.
LED is driven by constant current.

[lookimback]

Re: Use stripped TV as light/backlit sign. Ballast?

You could rewire the strips in parallel. I have an LED light box for photography. I used 25 strips of 5 LEDs. I replaced all the LEDs to get the correct color temp, but you wouldn't have to. I used a cheap 48v, 150 watt SMPS from China, and modified it so it output 31 volts. Figure out what voltage 1 strip requires, and if you have an ammeter, put it in series with your LED tester to find the current drawn. From there, we can figure out the required wattage for a power supply. The model number is S-150-48. I think it was under $15.

[budm]

Re: Use stripped TV as light/backlit sign. Ballast?

That typical LED tester can only put out maybe 30mA at most.
What you have to watch out is the amount of current being force through the LED, here is the sample graph of Vf vs If.
LED is the current device.

[JDC]

Re: Use stripped TV as light/backlit sign. Ballast?

A lot of great ideas here. So something that can put our 100V 300mA? Maybe 90v, doesn't need to be super maxed out bright.

[budm]

Re: Use stripped TV as light/backlit sign. Ballast?

The Voltage has to be high enough to forward bias the LED.

[lookimback]

Re: Use stripped TV as light/backlit sign. Ballast?

How many LEDs are there, and how many per strip?

[budm]

Re: Use stripped TV as light/backlit sign. Ballast?

What is the LED panel number? Panel Sticker Number: T390HVN02.2, HC390DUN-VCFP1-11xx, HC390DUN-VCFP1-21xx?????
http://www.shopjimmy.com/auo-t390hvn...s-8-strips.htm

36 LEDs, so at 300mA I expect the total Vf of the whole LED string (it looks like the LED strips are connected in series to form one long LED string) to be about 36*3.2V = 115V or so

[lookimback]

Re: Use stripped TV as light/backlit sign. Ballast?

What is the LED panel number? Panel Sticker Number: T390HVN02.2, HC390DUN-VCFP1-11xx, HC390DUN-VCFP1-21xx?????
http://www.shopjimmy.com/auo-t390hvn...s-8-strips.htm

36 LEDs, so at 300mA I expect the total Vf of the whole LED string (it looks like the LED strips are connected in series to form one long LED string) to be about 36*3.2V = 115V or so

So, if they were rewired in parallel, it would be 25.8v, still 300ma. Maybe find a 24v supply rated for a half amp. And that output could be adjusted to 25.8 if necessary.

[budm]

Re: Use stripped TV as light/backlit sign. Ballast?

When you wire semiconductors in parallel, the one with the lowest Vf will conduct, the one with higher Vf may conduct or may not conduct until the Vf threshold is met. You need series element (I.E. resistor, constant current control, etc. for each string.
https://www.edn.com/design/led/44245...el-LED-strings
https://electronics.stackexchange.co...ds-in-parallel

[lookimback]

Re: Use stripped TV as light/backlit sign. Ballast?

When you wire semiconductors in parallel, the one with the lowest Vf will conduct, the one with higher Vf may conduct or may not conduct until the Vf threshold is met. You need series element (I.E. resistor, constant current control, etc. for each string.
https://www.edn.com/design/led/44245...el-LED-strings
https://electronics.stackexchange.co...ds-in-parallel

I was thinking there should be a current limiting resistor for each string.

[budm]

Re: Use stripped TV as light/backlit sign. Ballast?

In TV that has mutiple string LED that are not connected in series to form one big string, they will have PWM Controlled power MOSFET and current sensing resistor on the low side to maintain constant current per string.

[lookimback]

Re: Use stripped TV as light/backlit sign. Ballast?

So, it's not as simple as just adding a current limiting resistor. Is it because the series resistance of the strip varies and changes with temp?

[budm]

Re: Use stripped TV as light/backlit sign. Ballast?

You can use resistor in each string, the resistor will take care of the current limiting string, but by using passive device, when the Vf of the LEDs changes, the current will change, but if you use constant method then the current flowing through will be constant regardless of the variation in the LED string. Using resistor is cheap if you do not care about the evenness of the LED lights.
Think of it this way:
You have 10V PS and 1K resistor as the current limiting element, and the load is 1K resistor then the current will be 5mA, if the load resistance has gone down to 400 Ohms, then the current flow will be more, opposite is true if the resistance goes up instead.

[lookimback]

Re: Use stripped TV as light/backlit sign. Ballast?

You can use resistor in each string, the resistor will take care of the current limiting string, but by using passive device, when the Vf of the LEDs changes, the current will change, but if you use constant method then the current flowing through will be constant regardless of the variation in the LED string. Using resistor is cheap if you do not care about the evenness of the LED lights.
Think of it this way:
You have 10V PS and 1K resistor as the current limiting element, and the load is 1K resistor then the current will be 5mA, if the load resistance has gone down to 400 Ohms, then the current flow will be more, opposite is true if the resistance goes up instead.

I see. So a resistor on each string would work if it isn't important that all the strings have the same brightness, such as maybe using them for lights under shelves in my shop. But, for something like a TV or a sign, where it would be noticeable and likely affect the device's usability, they should be driven by a constant current source.

[freakaftr8]

Re: Use stripped TV as light/backlit sign. Ballast?

Hence the reason I use a standard LED light bulb. I strip the plastic lens then strip the led's out and wire positive and negative into the LED strips of a TV wired in parallel