a7c0001aa01cj40 lcd panel voltage brands

Monochrome character, graphic and static displays require different input voltages. All the different LCD voltage symbols can be confusing, but believe it or not, there is a system to the madness.

The voltages VCC, VDD, VSS and VEE are used in describing voltages at various common power supply terminals. The differences between these voltages stem from their origins in the transistor circuits they were originally used for.

This LCD voltage terminology originated from the terminals of each type of transistor and their common connections in logic circuits. In other words, VCC is often applied to BJT (Bipolar Junction Transistor) collectors, VEE to BJT emitters, VDD to FET (Field-Effect Transistor) drains and VSS to FET sources. Most CMOS (Complementary metal–oxide–semiconductor) IC data sheets now use VCC and GND to designate the positive and negative supply pins.

In the Pleistocene era (1960’s or earlier), logic was implemented with bipolar transistors. NPN (Negative-Positive-Negative) were used because they were faster. It made sense to call positive supply voltage VCC where the “C” stands for collector. The negative supply was called VEE where “E” stands for emitter.

When FET transistor logic came around a similar naming convention was used, but now positive supply was VDD where “D” stands for drain. The negative supply was called VSS where “S” stands for source. Now that CMOS is the most common logic this makes no sense. The “C” in CMOS is for “complementary” but the naming convention still persists. In practice today VCC/VDD means positive power supply voltage and VEE/VSS is for negative supply or ground.

The convention of VAB means the voltage potential between VA and VB. The convention of using 3 letters was used to show power supply and ground reference voltages as well. In some cases a processor may have both an analog and digital power supply. In this case VCCA/VCCD and VSSA/VSSD are used. Another reason for the 3 letters is in an NPN circuit with a load resister between the collector and VCC. VC would be the collector voltage. In this case VCC is the positive power supply voltage and would be higher than VC.

Pin three (3) is Vo and is the difference in voltage between VDD and VSS. This LCD voltage is adjusted to provide the sharpest contrast. The adjustment can be accomplished through a fixed resistor or a variable potentiometer. Many products have firmware that monitor the temperature and automatically adjust the contrast voltage.

In a Liquid Crystal Display (LCD), V0 is used to vary the screen brightness or contrast. Contrast, simply put is the ratio of the light areas to the dark areas in a LCD. This is usually done in a production setting with values which are optimized for most users. Temperature can have an undesirable effect on the display brightness and for this reason a varying resister or potentiometer is used to accommodate the desires of the user.

Below is a data sheet of a 16x2 Character LCD module that shows various recommended driving voltages. The LCD voltage can range from MIN (minimum) to TYP (Typical) to Max (maximum).

If the supplied LCD voltage drops too low, the display is ‘under-driven’ and will produce segments that are ‘grey’. The lower the LCD voltage falls below the acceptable threshold, the lower the contrast will be.

If the LCD is over-driven, you may see ghosting. This is where segments that should not be ‘on’ are gray. They are not as dark as the segments that should be on, but they can be seen and may cause confusion for the end user.

There are times when a customer needs to replace a display that has been discontinued or EOL (End-Of -Life) by their previous LCD supplier. The previous LCD’s pin-outs may be different than Focus’ standard, off-the-shelf display. This is not a large problem to overcome.

The third option is to pull power from pins one and two. This is the same location from which the LCD is pulling its power. Focus does not recommend this option and can modify the PCB for the customer to connect the backlight from a different location.

Many LCD Modules will require more than one internal voltage/current. This may make it necessary for the customer to supply the needed inputs. They may need to supply 3V, 5V, 9V, -12V etc.

The solution for this is to integrate a charge pump (or booster circuit) into the LCD circuitry. This solution works in most applications, but if the product will be operating in an intrinsic environment, care must be taken with layout of the circuit board.

Intrinsically-safe LCDs are Liquid Crystal Displays that are designed to operate in conditions where an arc or spark can cause an explosion. In these cases, charge pumps cannot be employed. In fact, the total capacitive value of the display needs to be kept to a minimum.

Focus Display Solutions does not build a display that is labeled ‘Intrinsically safe’ but we do design the LCD to meet the requirements of the engineer. In meeting the design engineer’s requirements, the display may need to contain two or three independent inputs. Focus can redesign the PCB and lay out the traces to allow for these additional inputs.

LCD panel interfaces have changed over the years as resolutions have moved from 640×480 to 3840×2160. The following outlines the common ones that we support with our LCD controllers and cable kits. They cover most of the large size and higher resolution LCD panels on the market:

LVDS: LVDS was introduced in the late 1990’s and enabled connection for higher resolution panels with the benefit of reducing EMI. The LVDS interface is supported by most Digital View LCD controllers and covers panel resolutions from 640×480 to 3840×2160 though newer formats are replacing it for higher resolutions. It remains very popular for HD type resolutions, ie up to around 1920×1200. Most LCD panel manufacturers have LCD panels supporting LVDS, including AUO, BOE, Innolux, JDI, Kyocera, LG, Mitsubishi, Sharp, Tianma. LVDS is Low Voltage Differential Switching.

V-by-One: Increasingly common on 4K resolution panels typically 55″ and larger though I did find a 32″ 1920×1080 panel and 28″ 3840×2160 panel listed as in production. A benefit of V-by-One compared to LVDS is the reduction in cables for high resolution signal support and reduced EMI. LCD panel brands using V-by-One include AUO, BOE, Innolux, LG, Samsung, Sharp. I thought of V-by-One as replacing LVDS but apparently it was developed to replace FPD-Link.

eDP: First introduced in 2008 it is widely adopted by LCD panels used in laptops and similar devices. We are also now seeing it being used in higher resolution and brightness LCD panels but still typically smaller sizes, ie 30″ or smaller. Digital View LCD controller models supporting eDP include SVX-4096, SVX-2560, SVH-1920v2 and the new DD-1920-HDMI-EDPT. Brands using it include AUO, BOE, Innolux, LG, Panasonic, Samsung, Sharp, Tianma.

TTL: Supported by the ALR-1400v2 and HLR-1400v2 controllers this was the common panel interface when Digital View was founded in 1995. VGA (640×480) to XGA (1024×768) resolutions were mainstream at that time. Still used in commercial and industrial display applications AUO, Innolux, Kyocera, Mitsubishi, Samsung, Sharp, Tianma have LCD panels in production with resolutions such as 640×480, 800×480, 800×600, 1024×768. The name TTL is short for Transistor-Transistor Logic.

FPD-Link: The original low voltage differential switching signal but not to be confused with the LVDS interface on many panels as described above. It is now often used in the automotive market and currently up to FPD-Link III. It is not currently supported by any Digital View’s standard controller models though we are looking at it as a custom development option.

I skipped a few voltage tests on this repair as ive seen this before. i immediately was trying to determine if it was display vs tcon. unplug tcon, vertical bands dissapeared immediately and the tv was fine. Replaced tcon board and the tv would turn on and shut itself down. while trying to read cycling voltages on main board and tcon, about the 5th cycle, the vertical bands are back and again, dissapear when i unplug the lvds to tcon.

If it was the lcd display, the lines would still be present regardless of the tcon i suppose. if it is a voltage issue blowing the tcon, the display is just a feedback loop through tcon to main board as opposed to the main board being the output to the tcon. is my thinking in the ball park on this?

So this image is from the new board ordered, after power cycling a few times while getting readings. it would turn on and then shut itself down. like the original board, now the tv stays powered on with the lines. once i disconnect the tcon, the lines disappear and the tv stays powered on with backlight. Off of what you had posted in your reply @oldturkey03 , it appears that the driver boards are connected to the powerboard and the lcd panel. the tcon board is connected to the lcd panel and the main board. if the driver boards and tcon are connected on this unit, it is internal and through the lcd it appears. it looks weird haha. but to trouble shoot the driver boards, i have disconnected each side of the lcd boards one at a time and the the tv will go through post and shut down.