Samsung UN32F5500 with bad LEDs

[budm]

Re: Samsung UN32F5500 with bad LEDs

https://cdn.badcaps-static.com/pdfs/...96450c2ac1.pdf

The Vf will not be at 1V when forward current is at 200~300mA, do the experiment of the Vf VS If.
Vf of the LED varies with If and the temperature, same for diode.

[dskall]

Re: Samsung UN32F5500 with bad LEDs

I still say they should rename this forum to badbacklights.net

[dskall]

Re: Samsung UN32F5500 with bad LEDs

So there must be a way to lower the current and adjust feedback to take load off of leds

[budm]

Re: Samsung UN32F5500 with bad LEDs

Change the value of the current sensing resistor, you can limit the maximum value current to be up to the point that the circuit will still function.

[reyronaldo]

Re: Samsung UN32F5500 with bad LEDs

Resistors can be a good way to lower the current, but, if you are using high power LEDs with a few hundreds of mA, that will be tougher to drive. I suggest you use a switching current regulator instead.

[budm]

Re: Samsung UN32F5500 with bad LEDs

The LED driver in the TV is the constant current power supply, it regulates the curent by measuring the Vdrops on the current sensing resistor, the return current for the LED is through the PWM controlled Power MOSFET and then the current sensing resistor in on the Source pin, another end of the resistor is then to the circuit GND.

[reyronaldo]

Re: Samsung UN32F5500 with bad LEDs

Oh, yes, I agree the Vf is not 1V when If is 200-300 mA (high ampere) but 0.80-0.83V from the graph. Thank you.

[budm]

Re: Samsung UN32F5500 with bad LEDs

And it will be even less as the temperature goes up.
http://conceptselectronics.com/diode...aracteristics/

[reyronaldo]

Re: Samsung UN32F5500 with bad LEDs

I wonder if I can use a piece of 3v or 3v3 zener diode for every busted LED with voltage rating of 3-3.3v at a constant current supply of 200-500mA by the LED driver. What do you think?

[reyronaldo]

Re: Samsung UN32F5500 with bad LEDs

Yes, I confirmed using zener diodes for every busted leds (1:1) in reverse bias, instead of, using 1N4007 silicon diodes. I used a simulation software livewire and it did work well. Nice!!!

Note: Just use 1 Watt zener if constant current supply is below 300mA; 10 Watts for more than 300mA