4x20 634 Negative current draw


New member
I am looking to purchase a 634 4x20 serial LCD and the the negative backlit version caught my eye. However, to actually see the characters, does the backlight has to be on all of the time? If so, does it still use the same current draw as the standard backlit display (525mA or so)? I am concerned because this project will be running off of a 9v battery regulated down to 5v. Any info please?
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New member
Yes, the backlight has to be on all the time to see the characters. Also you will have to adjust the brightness & contrast levels when you get it working for the first time, and the characters display super bright on a washed-out, brighter-than-black background. (It won't resemble the advertised product pictures until you adjust the brightness & contrast levels)

As far as power draw I am not sure, sorry! :confused:

Oh something to add: if you don't adjust the brightness & contrast, the display runs pretty hot...at normal levels (illuminated charcters on black background) the display hardly generates any heat. You could logically assume that the higher brightness could increase power draw, unless at full brightness & contrast it already uses 525mA but decreases as you turn down the brightness & contrast...
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CF Tech

trophoblast is n the right track.

The backlight in the negative version is the same as the positive version.

The brightness is controlled by a PWM, so if the backlight is set to 50%, then the average current (and also power) will be reduced to 50%. Peak current is still the same.

If you are talking about a small rectangular 9v battery, the 525mA is going to discharge the battery very quickly. Plus, 4/9 of the power is going to be wasted as heat in the regulator.

It would be better to use 4 AA batteries in series (for 6v nominal) do the waste in the regulator will be smaller. Even then the big backlight on the 634 is going to chew through the batteries at a pretty quick rate.
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