Toasted my LCD screen

LCD was working perfectly until I was fixing something that wasn't broken ( bad habit of wanting to 'make it better' ).

Connected something incorrect, and the LCD has shown garbage since.

So got a new 20 x 4 screen today, but am a little unsure about the current for the backlight.

Datasheets for the 2 show the following for the backlight :

old LCD : Typical Vf = 4.2V ( min --- max 4.6 ) Typical If = 280 mA ( min --- max 480 mA )

new LCD : Typical Vf = 5.0V ( min --- max --- ) Max If = 260 mA ( min --- typical --- max 260 mA )

With the old screen, my 5V supply had a 1N4007 diode in series, and the reading at the LCD was 4.1V

I assume ( am guessing, so reason for the post ) that the diode dropped the current to the range required by the old LCD ( just the backlight ) and therefore no current limiting resistor was required, even though the backlight is ( I imagine ) an array of LEDs - because the voltage is the same as required by the backlight, it will only draw as much current as it needs from the supply ( which in this case is a 3A supply ).

My experience with LEDs to date has always been that they need a current limiting resistor, so I am a little unsure about this now.

If my understanding is correct, would it then also be correct that I should now remove the diode and supply the full 5V direct to the backlight, and as that is the same as required by the backlight, it will only draw the 260mA ( max ) mentioned in the specs, or would I now need a current limiting resistor ?

At present, I have the diode still in place, as well as a small resistor which has reduced the voltage to the backlight to 3.6V. It does light up, but understandably only very slightly.

Link to datasheet?

MarkT: Link to datasheet?

Hi MarkT

old LCD :

new LCD :

It appears the new unit has a built in resistor, so If I was me, I would give it 5 volts, which it states as typical.