attempt to clone LED TV Backlight Tester

[capwizard]

Re: attempt to clone LED TV Backlight Tester

Yes, one or two LEDs voltage drop more on the MOSFET . I will Put a switch for low and high voltage usage. low switch for one to one led strip testing, high switch for Dled tv whole screen and Eled tv strip testing. Or variable power supply.

[capwizard]

Re: attempt to clone LED TV Backlight Tester

RT7320 also provides a thermal regulation protection, instead of traditional thermal shutdown, to suppress the
rise of IC junction temperature and prevent LED lamps from flicker.


Page 3: Thermal Regulation Protection

When the IC junction temperature rises above 125°C (typ.), this
function starts to gradually reduce the regulated LED
current, depending on the rise of the junction temperature.
Meanwhile, the system power dissipation is also reduced.
Finally, the temperatures in the system will be well
controlled and enter their steady-state. The function can
achieve both of the two targets : to protect LED lamps and
to prevent them from flicker.

The maximum power dissipation can be calculated by the following formula :
PD(MAX) = (TJ(MAX) − TA) / θJA
where TJ(MAX) is the maximum junction temperature, TA is the ambient temperature, and θJA is the junction to ambient thermal resistance. For recommended operating condition specifications, the maximum junction temperature is 125°C. The junction to ambient thermal resistance, θJA, is layout dependent. For SOP-8 (Exposed Pad) package, the thermal resistance, θJA, is 29°C/W on a standard JEDEC 51-7 four-layer
thermal test board. The maximum power dissipation at TA = 25°C can be calculated by the following formula : PD(MAX) = (125°C − 25°C) / (29°C/W) = 3.44W for
SOP-8 (Exposed Pad) package The maximum power dissipation depends on the operating ambient temperature for fixed TJ(MAX) and thermal resistance, θJA. The derating curve in Figure 1 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation.

Is that mean IC never going to burn out?

At picture 2: When temperature rising to 125c, The power dissipation go to 0.0 w.

[llonen]

Re: attempt to clone LED TV Backlight Tester

Are you not better off just using a variable precision bench power supply with adjustable current limiting.

[budm]

Re: attempt to clone LED TV Backlight Tester

"At picture 2: When temperature rising to 125c, The power dissipation go to 0.0 w" It means at that point, there will be no current flow through the device to produce any heat, no Vdrops no heat, the higher the ambient the less current you can let it pass through the device otherwise it will be damaged.

[capwizard]

Re: attempt to clone LED TV Backlight Tester

llonen: using a variable precision bench power supply with adjustable current limiting.
B&K Precision 9803 The output can be varied from 0 to 300 V with 0.1 V programming resolution. $2,950.00 (Each)
http://www.alliedelec.com/b-k-precis...i9MaAsuc8P8HAQ

But our budget have only around $10. .

[llonen]

Re: attempt to clone LED TV Backlight Tester

Nice looking power supply, not one I would choose to testing back lights though,

I think I paid around £5.00 for one of these which I use for various applications including testing back-light strips.

https://wiki.london.hackspace.org.uk...0_Power_Supply

[capwizard]

Re: attempt to clone LED TV Backlight Tester

Nice,it could supply up to 60V DC. But To test edge led tv strips ( 4 of them for 60" ) each needs 186v dc, then you will need that plus 10x 9v battery to test.

[sardarshams]

Re: attempt to clone LED TV Backlight Tester

Hello
I need the schematic backlight tester Gj2c
thanks
http://www.ebay.com/p/Sid-Gj2c-LED-T...ter/1373031177

[capwizard]

Re: attempt to clone LED TV Backlight Tester

Mi amigo, está aquí..............Probador LED cuesta sólo $ 5. El probador es inseguro pero barato, por favor no lo use en armas nucleares.

https://www.badcaps.net/forum/showthread.php?t=59136

If you find this forum helpful? You might consider to donate here.

[capwizard]

Re: attempt to clone LED TV Backlight Tester

"I need the schematic for backlight tester Gj2c"

Although SID GJ2C is made in China, it may has copyright, but we teach you how to catch fish. you don't need the schematic, because you can make A better one, like battery powered Oled display LED tester or use microcontroller shows how many LEDs and protection diodes inside the screen and panel's suppose working voltage and current, would that be nice?

If you find this forum helpful? You might consider to donate here.

At the very bottom of this https://www.badcaps.net/forum/index.php page, Push the Orange button.

[sardarshams]

Re: attempt to clone LED TV Backlight Tester

"I need the schematic for backlight tester Gj2c"

Although SID GJ2C is made in China, it may has copyright, but we teach you how to catch fish. you don't need the schematic, because you can make A better one, like battery powered Oled display LED tester or use microcontroller shows how many LEDs and protection diodes inside the screen and panel's suppose working voltage and current, would that be nice?

If you find this forum helpful? You might consider to donate here.

At the very bottom of this https://www.badcaps.net/forum/index.php page, Push the Orange button.

thank you very much

[capwizard]

Re: attempt to clone LED TV Backlight Tester

You're more than welcome.
Eres más que bienvenido.

We are a bunch of electronic hobbyists to help each other like A big family.
And our mission is to Recycle the World.

[sardarshams]

Re: attempt to clone LED TV Backlight Tester

I wish the best for you

[rievax_60]

Re: attempt to clone LED TV Backlight Tester

I did some tests on a GJ2C loaded with resistors from 470 ohms to 10K. The open circuit voltage is about 330v. When I connect a resistor, there is a brief spike of about 5ma then it settles briefly to 1ma then it ramps exponentially for 2 to 3 seconds to about 30ma.
The built in voltage meter is accurate.

[capwizard]

Re: attempt to clone LED TV Backlight Tester

Thanks for your testing results.

330v dc / 1.414= 233.38v AC. So SID GJ2C use a 1 : 1 isolation transformer but over 110v AC region they use 1 : 2 isolation transformer or ac doubler. SID GJ2C testing voltage is DC 330v / 3v LED = It can test 110 LEDs

" ......to about 30ma. " Current is too high for LEDs long time testing. 110 LEDs x 30ma = 3.300ma = 3.3A

"..........then it ramps exponentially for 2 to 3 seconds" In pic1 We can change C2 to 10uf - 100uf capacitor, give the circuit 2 - 3 seconds to charge to 1.2v for it to reach the current limited. ( I constant = 1.2v / R).

[rievax_60]

Re: attempt to clone LED TV Backlight Tester

The interesting areas of the PCB are covered with a very tough black epoxy. There appears to be a MOSFET in series with the output that does the fast current control. There is a large drum inductor which must be part of a Buck regulator on the isolated side also.
The current ramps up in steps so must be controlled by the same micro-controller that does the voltage meter function.

[rievax_60]

Re: attempt to clone LED TV Backlight Tester

The TV had 2 series groups of 40 LEDs each. The tester developed about 150v for the 40 series LEDs.

[capwizard]

Re: attempt to clone LED TV Backlight Tester

"There appears to be a MOSFET in series with the output that does the fast current control. " My guess, it is the LR8 (HV version of LM317)?

" a large drum inductor which must be part of a Buck regulator on the isolated side also." My guess, That is for smooth the output voltage?

"The current ramps up in steps so must be controlled by the same micro-controller that does the voltage meter function." My guess, U6 only uses for voltage meter? The current ramps up using capacitor.

PS: Why they use Epoxy because they don't want you to know it is so easy to built.

The poormans LED tester current is at 6.8ma, with no ramps up current I can calculate LEDs characteristics. Pic2.

[gabiz_ro]

Re: attempt to clone LED TV Backlight Tester

" ......to about 30ma. " Current is too high for LEDs long time testing. 110 LEDs x 30ma = 3.300ma = 3.3A

That's wrong
Current is 30mA no matters LED's number.
110 Led's -> 330V
330V x 0.03A (same 30mA as people say previous) = 9.9W
Almost 10W,I think is a little too much for simple or single LR8K

Also I don't see isolation transformer or 1:1.
Could be live connected.
Also for 110V line could be using some voltage doubler.

That little transformer could be some part of SMPS that deliver power to microcontroller and 330V at 30mA or only for microcontroller and LED's voltage is from main line.

More clear and detailed photos can be usefull to solve the mistery.

[capwizard]

Re: attempt to clone LED TV Backlight Tester

You're right.....My bad, Constant current means all LEDs in series at 30ma.

"Also I don't see isolation transformer or 1:1." This I just guess because I did not have this LED tester.