voltage divider for vizio hack

[goontron]

i have attached a small diagram for the voltage dividers the purpose of the dividers is to provide driving voltage to an older vizio lcd tv inverter board to cause it to act as a lighting fixture. my question is: will it provide the correct current at 3v to switch the inverter?

[budm]

Re: voltage divider for vizio hack

Power on can be connected to the +5V through 1K resistor, same for the BL_ON signals, the ON signal is used for driving the BASE of the transistor, so it only need the current in mili-amp range. You will also need the dimming signal control signal which can be PWM type or analog 0~5VDC variable signal.
The bl_0n signal should be delayed on after the power supply on signal is applied because you want the power supply to be stable first before trying to draw lots of current when the inverter is turned on.
You should look up the spec of the LCD panel, it will give you all the pinout of the boards on the panel.

[goontron]

Re: voltage divider for vizio hack

the inverter dims by the controller pulling voltage down on the dimming rail but i don't want dimming so that can be left alone. for delaying the BL_ON signal i wouldn't have a clue.

[budm]

Re: voltage divider for vizio hack

So it is using analog dimming then? 5V= Max brightness, 0v = min, 2.5V = 50% brightness.

[goontron]

Re: voltage divider for vizio hack

So it is using analog dimming then? 5V= Max brightness, 0v = min, 2.5V = 50% brightness.

dim to no connection=full bright, dim to gnd=off and the delay for BL_ON still has me.

[budm]

Re: voltage divider for vizio hack

That sounds like it uses PWM dimming instead of analog dimming. You may be able to get simple delayed on by using RC delay circuit, the timing will have to be figure out what it should be by looking at the spec sheet of your LCD panel.
See example on page 16 for the timing, notes the spec attached does not have PWM dimming, but yours may have both options.

[goontron]

Re: voltage divider for vizio hack

its going over a reptile tank so it doesn't need dimming

[budm]

Re: voltage divider for vizio hack

OK, then you will just need about 1 second delayed on circuit the for the Backlights on signal.

[goontron]

Re: voltage divider for vizio hack

how would i do that?

[budm]

Re: voltage divider for vizio hack

See this thread here:
Notes: the Anode of the Diode will be connected directly to the Gate of the MOSFET, no cap between the Anode and the Gate, or you can leave out the Diode and the 100 Ohms resistor (they are for quick discharging the timing cap when the TV is powered off).
https://www.badcaps.net/forum/showth...elayed+circuit

[goontron]

Re: voltage divider for vizio hack

i just realised its an lg inverter part# 3pcgm10002a-r with no 24v or bright.

[budm]

Re: voltage divider for vizio hack

Same timing still applied for the BL_ON pin. If you can monitor the PS_ON pin and the BL_ON pin when you turn on the TV, you will see the bl_on will happen second later after the PS_ON signal. That inverter uses 380VDC to run it.

[goontron]

Re: voltage divider for vizio hack

ok i get it now, could i replace A1 with a switch and 1k resistor to 5v stby?

[goontron]

Re: voltage divider for vizio hack

do you think this schematic will work?
btw the voltage on these things can cause an arc to jump, in this case to my finger! ouch

[tom66]

Re: voltage divider for vizio hack

That is excessively complicated.

Just use a 10k resistor and 47uF capacitor in series; output across the capacitor. 10k limits current due to 3V logic input. Delay = 3 * R * C = about 1.5 seconds.

[budm]

Re: voltage divider for vizio hack

At 10K x 47uF = 1TC of 0.47 second. At 1 TC the cap will charge up to 63% of the applied voltage, so at 5V after 1TC, the voltage on the cap will be 3.15V which will be within the ON volatge range. 10K can be too high since we do not know the input resistance we are feeding, it may be enough to bias the transistor.

[tom66]

Re: voltage divider for vizio hack

OK, 470 ohms usually works, and a large capacitor of 1000uF gives 1.41 seconds, assuming charging up to 5V. Charging stop voltage can be lowered by adding a resistor in parallel with the cap, around 680 ohm would work.

[budm]

Re: voltage divider for vizio hack

See COMPLEX CIRCUIT for parallel/sereries RC circuits.
http://openbookproject.net/electricC.../DC/DC_16.html

[goontron]

Re: voltage divider for vizio hack

would a 555 timer like this work?

[tom66]

Re: voltage divider for vizio hack

Since you are using gschem (I do too), try zooming in closer and selecting 3200x2400 when exporting the image, and we may be able to see it clearer, at present I cannot see anything there and I doubt anyone else can.