How to power MT6820-B controller

[omer123]

How to power MT6820-B controller that connect to the panel with universal 1ch 6bit 40pins
lvds cable ?
The panel specification is :
                                                  Min.  Typ.  Max.
Power Supply Voltage VCCS     3.0    3.3    3.6
                                                                                   Min.   Typ.    Max.

Converter Input power supply voltage LED_Vccs       6.0    12.0    21.0

 

                                                                             Min.     Typ.     Max.
LED Light Bar Power Supply Voltage VL               28.6    31.9     33

 

 

Thanks in advance

[mariushm]

Some pictures of the board would help.

Usually there's just one input (ex 12-18v) and a voltage regulator on the board produces 3.3v so you don't need separate 3.3v input .. but no idea without pictures of the board. 

Check the board, look for printed text by the headers...

 

[omer123]

41 minutes ago, mariushm said:

Some pictures of the board would help.

Usually there's just one input (ex 12-18v) and a voltage regulator on the board produces 3.3v so you don't need separate 3.3v input .. but no idea without pictures of the board. 

Check the board, look for printed text by the headers...

 

The lvds cable:
https://www.aliexpress.com/item/32958971843.html
6 power wires plug to the board power socket
https://www.aliexpress.com/item/4001343641436.html

GND
GND
5V
5V
ADJ
BL

 

[mariushm]

The LVDS cable only carries the data and some voltage (3.3v or 5v) to the chips on the LCD panel.

The power required to power the backlight is not sent through that cable.

 

The controller board in the second link is only the video processor, the chip which takes the VGA signal and processes it (optional rescaling, cleaning up etc) and sends the digital conversion through the LVDS cable to the LCD panel.

It's powered by 5v through that connector - you have there two background pins and two 5v pins.  The connector also has ADJ and BL which are adjust brightness, and backlight enable pins ... those go to a separate backlight driver board which takes in some voltage (typically 10v...24v) and produces the voltage required to light up a CFFL backlight, or the LED strips inside the panel.

Adjust brightness is a signal produced by that video processor on the board and goes to the backlight driver board to control brightness.

BL enable is an on/off for the backlight - think for example when the monitor is in stand-by / sleep, the video processor can send the command to the backlight driver to turn off backlight..

 

If the LCD panel has CFFL lamps (like fluorescent tubes), then you need a universal backlight driver for CFFL, here's an example:

 

4 lamp backlight driver : https://www.ebay.com/itm/183586913336

connector is simple ... voltage x 2 (min 10v, max 25v) , backlight enable, adjust brightness, ground x 2

2 lamp backlight driver : https://www.ebay.com/itm/273658959472

same connector

 

You panel seems to have a LED backlight ... so you'd need to figure out the voltage (apparently it's 28.6 .. 33v) and the current amount.

 

You must limit the current otherwise the leds will blow up.

Basically that forward voltage of 28..33v tells you the monitor probably has 10 x 3v leds in series or groups of 10 x 2.8v..3.3v leds in series ... or maybe 5 x 6v leds in series

 

If the individual leds are rated for 60mA  and you have 50 leds on each led strip and there's groups of 10 leds in series, that means there's 5 groups of 10 leds, and each group consumes 60mA, so your led driver must be limited at 10 x 60mA = 600 mA of current ... you'll probably want to limit it at 500mA.

 

Here's for example a LED driver board from a ViewSonic monitor, which can drive up to 4 led strips : https://www.ebay.com/itm/373898268156?hash=item570e12cdfc:g:7PQAAOSwFmNh7WtR

Same connector with input voltage, backlight enable, adjust and ground

 

 

If you look at the picture, you can read the code of that led driver chip, which is OB3365RP , from OnBright ... and here's the datasheet for it : OB3362RP.pdf

 

So you get some valuable information from the datasheet...

First page tells you chip's input voltage is 6v...30v so probably 10-12v would make sense, and 16.5v..19v from a laptop adapter would also work.

 

In the typical application example on first page, you can see PIN 5 is ISET which means set current , and page 7 tells you the current must be between 18mA and 200mA on each channel,  and formula is   Current = 3000 x 1.2v / resistor value  ... so for example if a 20kOhm resistor is used, then current would be limited to 3600 / 20000 = 0.18A of current on each of the 4 channels / led strips.

 

The chip is upside down in the picture, pin 1 is on bottom right where that dot is in the corner, so you go up and 5th pin is the max current ... and I think - but not sure - the circuit board above uses two resistors in parallel to get a more precise current value set.

 

Page 10 in datasheet even has an example circuit with resistor values for the settings listed under the schematic (10..30v input voltage, 180mA per channel, 10 leds per channel)

[omer123]

Thanks for the detailed answer mariushm

 

[omer123]

Is powering typical 12V backlight panel with 5V
can damage the panel in the long term use ?
https://youtu.be/qLR4iiOV1Sg?t=237

[mariushm]

In the video, he's using a 14" 1366x768 6bit per color (meh) panel with led backlight driver on the circuit board, from AU Optronics, model B140XW01 v0 

 

So you can get datasheet of the panel ... Ihere's the v.0  datasheet:  http://www.yslcd.com.tw/docs/product/B140XW01 V.0.pdf

 

On page 11, you can see LED power in the connector, and you can see there's a LED Boost and current balance circuit which boosts the input voltage to the voltage needed for the led light bar. 

 

 

Page 13 tells you that the LCD panel needs 3.3v and up to 364 mA  or 1.2 watts ... so most likely there's a small linear regulator converting 5v to 3.3v on the circuit board on the panel or the processor board has a 3.3v regulator. Either way, the idea is that your power supply should reserve around 1.5 watts for the lcd display. 

 

page 15 tells you the backlight properties..

 

They use individual leds with forward voltage between 2.8v and 3.4v (typical 3.2v)  and each led uses 20mA or 0.02 A  and the total power consumption (at 100% brightness) would be 3.36 watts.  So this tells you that the led strip has 3.36 w / 3.2v (typical forward voltage of 1 led) / 0.02 = ~ 52 leds in the led strip.  I would be more conservative and say most likely there's 48 leds, arranged in 3 groups of 16 leds, which means the led boost and current balance circuit takes 7v...21v and boosts it to 3.2v x 16 = ~ 51v   

 

 

So the input voltage for the LED backlight recommended here is MINIMUM 7v, TYPICAL 12v, MAX 21v   but if you go down to page 18 and 19 you will see there they recommend  "LED power supply 7.5v... 21v"  

 

So basically that LED Boost and Current Balance circuit" takes the input voltage (7v...21v) and boosts it up to be at least equal or higher than the voltage of the leds in series in the backlight - if I'm right, that would be 16 leds x 2.8v..3.2v typical forward voltage per led = 45v..52v 

 

The circuit is designed to multiply the input voltage by some ratio, in this case it seems to be 7v -> 52v = 7.5x times   and the lower range would be 21v -> 52v = ~ 2.5x ... so it wants to multiply voltage by 2.5x ... 7.5x max. 

 

If you power it with 5v,  you're basically forcing the chip to multiply the input voltage almost 10 times, as you do 5v -> 52v  = 10x

So you're stressing the chip and the components it uses to boost the voltage.  You could overheat the chip or you could gradually damage the components used by the chip, and eventually after a few hours or hundreds of hours of operation, those components could break. 

It may work, it may not work. 

My advice would be to aim for powering with a 9v or a 12v power supply. You could use a 5v linear regulator (7805 , LM317 , LM1084) to get 5v from 9v...12v. 

 

Your power supply would have to able to provide at least 1.2 watts for the LCD panel and at least 3.5 watts for the led backlight.... so I'd use a 5w power supply  

 

Keep in mind that the lower that multiplier is, the more efficient that led backlight driver would be.  If you power it with 5v or 7v, the minimum, that circuit may be only 80 efficient at boosting the voltage to 50v or whatever is needed, so your 3.36w backlight circuit may need 4w to work.  

But, if you power it with 12v...19v, the circuit may be 90% efficient and your 3.36w backlight may need only around 3.5 watts to work.

 

 

[mariushm]

Alternatively, if you must insist on using 5v  (if you want to power it from a USB port on your computer), get a boost (step-up) dc-dc regulator , you can get cheap, basic ones on eBay for a dollar or two. Here's some examples : 

 

1$ with MT3068 chip : https://www.ebay.com/itm/113229103989  or  https://www.ebay.com/itm/284012265284

Set the output to 9..12v (adjust with potentiometer) and you're good to go.   connect ground to Vin- and Vout-  , Vin+ to 5v, Vout+ to the display wires that carry voltage to the backlight circuit.

 

1$ with SX1308 chip : https://www.ebay.com/itm/400985272876

same story, adjust voltage to 9v..12v using the potentiometer and you're good. 

 

~2$ with XL6009 chip : https://www.ebay.com/itm/393900099653

same deal

 

[omer123]

Can you recommend a power supply with 3 out wires - 12V,5V and ground -

that will fit for direct connection ?