Polaroid P40LED13 fixed

[tom66]

Found in the trash area at my apartment block.

Was powering on with no backlight but faint picture visible under flashlight.

This set had *five* open circuit LEDs. I bridged them all as it is a series string with constant-current regulation for the whole string, so this is acceptable.

Now fully working. 12,100 hours on the internal hour counter.

Going to set backlight to the medium setting as high setting is too much current for these LEDs obviously.

[budm]

Re: Polaroid P40LED13 fixed

PWM Controlled power MOSFET is not getting too hot due to more Vdrops on the MOSFET?

[tom66]

Re: Polaroid P40LED13 fixed

No, the power supply drops the voltage. It is a constant current regulator with all LEDs in series.

[budm]

Re: Polaroid P40LED13 fixed

Most LED driver has fixed boosted output Voltage and the use the PWM Controlled MOSFET to regulate the current on the return side, I had to replace many the burnt MOSFET when people bypassed the bad LEDs so the Vdrops on the MOSFET goes up and caused it to over heat.
What kind of LED driver IC is used in that TV?

[tom66]

Re: Polaroid P40LED13 fixed

http://www.monolithicpower.com/Deskt...cument?id=1260

It would appear that the IC regulates the boost current from the sum of the LED currents, according to the diagram on page 8.

Though I can't be sure - I misread current-mode as current-controlled on the first page.

The regulation MOSFETs are inside the device, so it cannot dissipate much power. All four channels are tied in parallel. The design of the set allows for many different configurations to be used which makes interpreting the labyrinth of the schematic () difficult.