LCD power supply VO

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jetro57070
LCD?
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Joined: Thu Jun 22, 2006 9:51 am

LCD power supply VO

Post by jetro57070 » Thu Jun 22, 2006 9:56 am

Why is the LCD voltage different than the logic power supply? The datasheet shows a pot to create VDD-VO at the VO pin on the LCD. is this for contrast? I thought contrast is controlled by software commands.

Also why would you need a pot? datasheet shows VDD-VO to be 0.5v, why not use a voltage divider? or tie them both together?

Raquel
Matrix Orbital
Matrix Orbital
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Post by Raquel » Thu Jun 22, 2006 1:30 pm

Hi jetro57070,

Thank you for posting on the forum.

The MOP series does not have software controlled contrast. If you go to our website (www.matrixorbital.com). The Parallel (MOP) series is one of the few series that does not have software controlled contrast.

The pot in the datasheet is suggested so that you may be able to easily have a range of contrast which will suit different lighting conditions.
Raquel Malinis
Design and Development
Matrix Orbital

AlphaByte
LCD?
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Joined: Tue Feb 03, 2009 3:33 pm

Re: LCD power supply VO

Post by AlphaByte » Fri Jun 04, 2010 6:28 am

jetro57070 wrote:Why is the LCD voltage different than the logic power supply? The datasheet shows a pot to create VDD-VO at the VO pin on the LCD. is this for contrast? I thought contrast is controlled by software commands.

Also why would you need a pot? datasheet shows VDD-VO to be 0.5v, why not use a voltage divider? or tie them both together?
Optimal contrast occurs at a very specific voltage. This voltage is beyond
the 5 volt range of the LCD controller. It occurs close to about -7V with
respect to ground. That's about -12V with respect to the 5V rail.

The display module circuit board contains a chip called an inverting voltage
tripler. 5V x -3 = -15V. That -15V is output on pin 20, adjusted by the
divider on the application board, and returned to the display module at V0.

On the display module the V0 is used to generate V1 though V5 for LCD
waveform generation.

In a nutshell, liquid crystal requires more than 5V to polarize.

Clark
Matrix Orbital
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Post by Clark » Fri Jun 04, 2010 4:19 pm

Hi AlphaByte,

Thanks for the info, it'll provide a great insight for our MOP community.

To clarify your point, our alphanumeric units are usually readable with an LCD supply voltage of around 0v, however, our graphic units will definitely need negative voltage. A negative voltage output will be provided on many of our graphic units, but if need be the info and circuit information you have provided will be a great help.

~Troy
Troy Clark
Design & Development
Matrix Orbital

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