Hi all,
We are working on a project that is using an Optrex DMF-50840 LCD display
module. As in many (most?) LCD displays we need to supply a drive voltage in
the range of -15V to -25V (I am waiting for details on the current
requirements). Does anyone have experience with these things who can shed some
light on the current requirements? I am also very, very interested in the ways
people have generated these voltages. We may only have a +5V supply available
(not fully defined yet). Any suggestions are greatly appreciated. Thanks.
Mark A. Corio
Rochester MicroSystems, Inc.
200 Buell Road, Suite 9
Rochester, NY 14624
Tel: 716-328-5850
Fax: 716-328-1144 http://www.frontiernet.net/~rmi/
****** Designing Electronics for Research and Industry ******
>Hi all,
>We are working on a project that is using an Optrex DMF-50840 LCD
display
>module. As in many (most?) LCD displays we need to supply a drive
voltage in
>the range of -15V to -25V (I am waiting for details on the current
>requirements). Does anyone have experience with these things who can
shed some
>light on the current requirements? I am also very, very interested in
the ways
>people have generated these voltages. We may only have a +5V supply
available
>(not fully defined yet). Any suggestions are greatly appreciated.
Thanks.
Very little. mAs or less. A charge pump, or inverting boost converter
would serve well.
> Hi all,
> We are working on a project that is using an Optrex DMF-50840 LCD display
> module. As in many (most?) LCD displays we need to supply a drive voltage in
> the range of -15V to -25V (I am waiting for details on the current
> requirements). Does anyone have experience with these things who can shed some
> light on the current requirements? I am also very, very interested in the ways
> people have generated these voltages. We may only have a +5V supply available
> (not fully defined yet). Any suggestions are greatly appreciated. Thanks.
The easy way is, to use a canned converter for this purpose (usually makes
-28V from +5V). Displays do not draw serious current through the - supply
unless they are graphical color displays, which changes the figure
completely. 30 mA @-26V peak for B/W at 640x200 is a real figure. Jameco
and Mouser have some of these in their catalogs.
The other way is, to have a power supply that already gives -28V. Laptop
modular supplies do just that.
The third way is, to make this voltage using a converter.
Note that large color displays change the requirements completely, and
often only work with the recommended power supply (in a can).
There are issues re: the order of voltage turn-on and turn-off both to
meet the specs of the LCD and to prevent all the pixels from becoming
visible or 'washed out' during power cycling or after switch-off.
The current requirements for the LCD itself are minimal, in the picoamp
range. To
make this contrast voltage adjustable, connect a pot across the source of
the contrast voltage, and feed the output from the wiper of the pot to the
LCD module.
As to how to generate this voltage, you can use a LDO (Low Drop Out)
switching voltage regluator in the buck mode to generate the negative
voltage required. Suitable regulators of this type are available from many
sources, but I have had good luck with MAXIM parts.
Another way to generate this voltage, and I've done this several times, is
to connect two 9 volt transistor radio batteries in series, and use that as
the source. From this point on out it is the same as mentioned above. The
batteries will last almost as long as their shelf life. This would be okay
for development, but for production I recommend the regulator route.
Hope this helps you out.
Regards,
Jim
----------
> From: Mark A. Corio <spam_OUTMcorioTakeThisOuTAOL.COM>
> To: .....PICLISTKILLspam@spam@MITVMA.MIT.EDU
> Subject: LCD drive/ contrast adj voltage generation
> Date: Thursday, October 15, 1998 10:17 AM
>
> Hi all,
> We are working on a project that is using an Optrex DMF-50840 LCD display
> module. As in many (most?) LCD displays we need to supply a drive voltage
in
> the range of -15V to -25V (I am waiting for details on the current
> requirements). Does anyone have experience with these things who can shed
some
> light on the current requirements? I am also very, very interested in the
ways
> people have generated these voltages. We may only have a +5V supply
available {Quote hidden}
> (not fully defined yet). Any suggestions are greatly appreciated. Thanks.
>
> Mark A. Corio
> Rochester MicroSystems, Inc.
> 200 Buell Road, Suite 9
> Rochester, NY 14624
> Tel: 716-328-5850
> Fax: 716-328-1144
> http://www.frontiernet.net/~rmi/
> ****** Designing Electronics for Research and Industry ******
About that negative voltage thing...
Say I have some logic or micros controlling the display, and I need
about -12 V for my LCD, would connecting a +5V supply and a +12V
supply in series do the trick? Say I connected the - side of the
12V supply to the - LCD supply, and + side of the 12V supply and the
- side of the +5V supply to the system ground, and then just used
the + side of the +5V supply to power the logic... Would this
suffice? Or will something fry if I did this? I saw something
similar to this to make a -12V - 0 - +12V supply somewhere...
>Hi all,
>We are working on a project that is using an Optrex DMF-50840 LCD display
>module. As in many (most?) LCD displays we need to supply a drive voltage
in
>the range of -15V to -25V (I am waiting for details on the current
>requirements). Does anyone have experience with these things who can shed
some
>light on the current requirements? I am also very, very interested in the
ways
>people have generated these voltages. We may only have a +5V supply
available {Quote hidden}
>(not fully defined yet). Any suggestions are greatly appreciated. Thanks.
>
>Mark A. Corio
>Rochester MicroSystems, Inc.
>200 Buell Road, Suite 9
>Rochester, NY 14624
>Tel: 716-328-5850
>Fax: 716-328-1144
>http://www.frontiernet.net/~rmi/
>****** Designing Electronics for Research and Industry ******
>
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