attempt to clone LED TV Backlight Tester

[rievax_60]

Re: attempt to clone LED TV Backlight Tester

The photo in post 38 is different. The one I have has more parts.

[rievax_60]

Re: attempt to clone LED TV Backlight Tester

I took some photos of its PCB. Although it was purchased by someone else, I think the price is reasonable.

[budm]

Re: attempt to clone LED TV Backlight Tester

The more LEDs in series the less power dissipation for the LR8K because you will have less Vdrops on the IC, it is worst when you test 1 LED.

[gabiz_ro]

Re: attempt to clone LED TV Backlight Tester

That's right.

On my attempt to build one,testing one single LED,input voltage was drop to 140V (due to my setup) LR8K4 was configured for 10mA and mounted on little heat sink.
After few minutes 5-10 heat sink was a little warmer than my fingers.

As for voltage drop that I said previous,I try to keep it safe,isolated from mains.
So I use two little (too little) transformers until I found one little enough 1:1
Their specs was 230V 60mA input 6V 400mA output
But was not enough,voltage dropping too much.

[capwizard]

Re: attempt to clone LED TV Backlight Tester

rievax_60 Thank you for the fotos. This one do has a MOSFET, Maybe they designed similar to this circuit.

gabiz_ro Would you please try to design A battery powered LED tester? If you have time.

[gabiz_ro]

Re: attempt to clone LED TV Backlight Tester

Using some boost converter may be done.

Looking for something like that I see this
https://www.amazon.com/Qianson-Volta.../dp/B01J2T48L6

but not clear what say

Output current: 2-20mA.( if you want to add current, pls put insurance below the transformer replaced the 0ohm resistor, maximum 50mA, but does not recommend increased.)

We need 300V at 20-30-40mA
It may be enough even at 20mA if description is for real.

Or better this
https://www.amazon.com/gp/aw/d/B01JL...ID=61guzKBeQpL
But seems to powerfull for that.

[redwire]

Re: attempt to clone LED TV Backlight Tester

I whip together a HV constant-current source using depletion mode MOSFET. It needs a heatsink because it is in linear mode. It's a couple resistors and a diode, good to 400-1,000V. Then I use any HV DC power supply.
See:
IXYS 10M45S and Supertex DN2540
IXYS IXTP08N100D2 depletion mode MOSFET 1,000V

Resistor calculator here

[capwizard]

Re: attempt to clone LED TV Backlight Tester

i never heard.... Switchable Current Regulators IXCP 10M45S...People used for Tube Asylum(tube current source). Thank you, I've learned from you.

Why can we use junk LED power board from manufacturer, Modify it to A variable current and variable voltage power source.........From the feedback of the driver IC maybe it just needs two Potentiometers for voltage divider. .......... as A LED tester and LEDs strips (screen) power supply? This gonna be my next homework.

[capwizard]

Re: attempt to clone LED TV Backlight Tester

SID GJ2C's competitor. it Looks like a AC Adapter, LED voltage meter + current mode boost converter of which is for higher current purpose.

Who knows in the picture (pic4) the question mark aera circuit is for?

[gabiz_ro]

Re: attempt to clone LED TV Backlight Tester

May be some voltage comparator.
Nothing connected SMPS is driven by optocoupler D1
Some LED's connected depending on voltage resulted D2 or D3 override somehow D1 as result SMPS output could be 50V or 150V or 300V
That decrease power disipated by series regulator.

But maybe I'm wrong.Who knows.

[capwizard]

Re: attempt to clone LED TV Backlight Tester

More LED testers, they copy each other's circuit.............

I bet yu. Next generation LED tester will be battery power, V & A adjustable, OLED or LCD V And A display, Microcontroller shows what type LED and how many of LEDs in one or total strip, LEDs brightness(LUX) and and lifetime span.

With WiFi add -on the tester will reach the Database and finds out what kind screen youre testing and who made that LEDs or LED strips by reference current, voltage, LUX, and wattage parameters. By that time, we don't need LED tester (as CCFL tester anymore), we will need is OLED tester.

[budm]

Re: attempt to clone LED TV Backlight Tester

https://www.badcaps.net/forum/attach...5&d=1490812596

Hmm something is not right, it shows 20 LEDs, but the Voltage reading is showing 18.1V

[budm]

Re: attempt to clone LED TV Backlight Tester

SID GJ2C's competitor. it Looks like a AC Adapter, LED voltage meter + current mode boost converter of which is for higher current purpose.

Who knows in the picture (pic4) the question mark aera circuit is for?

https://www.badcaps.net/forum/attach...9&d=1490803893
The section you marked as 'CURRENT MODE BOOST' is the hot primary side SMPS showing the SMD power MOSFET driving the primary winding of the power transformer, you can see the Drian pin connected to one pin of the transformer and the RCD Snubber network (R2, C3, VD8).

[capwizard]

Re: attempt to clone LED TV Backlight Tester

" it shows 20 LEDs, but the Voltage reading is showing 18.1V" ............18.1v / (20 / 2) = 1.81v The color of LEDs are amber because they are cheaper than white one. http://www.torchstar.us/5m-5050-ambe...ip-lights.html

[budm]

Re: attempt to clone LED TV Backlight Tester

They look white to me, unless the photo is not color corrected.

"18.1v / (20 / 2) = 1.81v " are they two strings of 10-LED per string connected in parallel?

[capwizard]

Re: attempt to clone LED TV Backlight Tester

"18.1v / (20 / 2) = 1.81v " are they two strings of 10-LED per string connected in parallel?

Yes it is.

pic1 : Clone LED tester for sale $14.90 but shipping and payment ? Be careful.

[budm]

Re: attempt to clone LED TV Backlight Tester

Link to that LRF?

[vinceroger69]

Re: attempt to clone LED TV Backlight Tester

https://www.hklrf.com/0-300V-Smart-F...pair_1948.html

I have just tried to create a account it says a extra 10.10 postage to the uk

[budm]

Re: attempt to clone LED TV Backlight Tester

https://www.hklrf.com/0-300V-Smart-F...pair_1948.html
Notice:
Please, if you are used to the LED lamps finished, unplug the power supply before!
Because it is likely to form a loop, which in Abnormal test!
Additional application:
The capacitance voltage
The voltage regulator
worth 3 lamp drive voltage test!
Examination skills:
Plug IN POWER, it can be used after 5 to 10 seconds (first time, the machine needs to warm up!).
Soft Start mode make the backlight brighter always slow.
No burning, if you can not make the "+" and "-", do not connect the probes to the LED will be tested for a long time.
Open ciruit protection: Do not touch the output terminal of probes for a long time. It is safe for Touch the probes in the shortest time.
Double isolate design makes our testers safety with high strength and flame retardant materials.
Safe / smart / precise / highly efficient
Double isolated safe protection no burning, no electric shock, voltage and current intellgent setting,
High brightness disassemble no need.
Single LED light bar backlight check:
make sure the anode and acthode.
connect the probes to the anode and the cathode.
light up the single LED light bar backlight.
light up the double LED light bar backlight.
So these testers have the so called SOFTSTART circuit that ramp up the Output Voltage, so if you turn it on and not connected to any load (LED) then I expect the output Voltage will reach 300VDC (unless it has open circuit protection) then if you connect the output probe to ONE LED, I wonder if the circuit will react fast enough to drop that output Voltage down to 3V and not damaging the LED since if there is filter cap at the output then that cap will have to be discharged to drop the Voltage down. Any one out there has one to try out.

BTW, I wonder what this means "Because it is likely to form a loop, which in Abnormal test!"

[vinceroger69]

Re: attempt to clone LED TV Backlight Tester

budm is it true that a shorted led can still light up? im sure ive read somewhere they can.