Hi,

I am using MCCOG21605B6W-SPTLYI LCD(Display) in my project. I need to dimmable the LCD.How I need to do this?



Best regards,
Vivek Alaparthi

 

Don't know about dimming. Most displays have a contrast adjustment which is controlled by a potentiometer or a voltage source.

After that you may need to use an explicit command to the display to set one or more discrete brightness levels.

 

Are you trying to dim the back-light of the LCD so it appears not too bright when all the surrounding lights are out?

Allen

 

Hi Allen,

I need to dimmable the LCD for long life. The LEDS inside this display must be supplied with typical current 32mA. Then the lifetime of the display will be around 50000 hours. I dont understand why this bjt is used in the circuit???


Best regards,
Vivek Alaparthi

 

The transistor is functioning as a switch controlled by a voltage (there must be a resistor in series, which isn't shown) coming in on the LCD B/L line.

If you want the backlight dim all the time, replace the 33 ohm resistor with a larger one. Or, pulse the LCD B/L line. But then what you'd be doing would be to alternate the LEDs between full brightness and off, which might actually be worse than running them at an even current. Is there some way you can run the LEDs under user control, only driving them when you need to look at the display?

 

Replace the 33 ohm resistor with a 1000 ohms preset so you can dim it like this...


http://cpc.farnell.com/bourns/3006p.../dp/RE04182?in_merch=Products From This Range

 

Hi john,


Thanks for your reply. I have modified the circuit as shown below. Can you please check whether this will work out or not



Thanks & regards,
Vivek Alaparthi

 

Don't run this circuit! You are likely to destroy the LEDs.

I see what you're trying to do, have a "bright" and a "dim" setting. And maybe you didn't actually remove the 33 ohm resistor, but just left it off the diagram. If so, no problem. You can run the "dim" setting with the 33 ohms in place--compared with 1K, it's almost negligible, but it has to be there for the "bright" setting. I'm slightly surprised that the lights are usable with 1K in series, but if it works for you, then that's fine.

Incidentally, both transistor bases are running off "LCD-B/L". I assume that's not the real intention.

 

Hello John,

Thanks for your reply,
Ithink this will work.

Generally what resistance is good to run the LEDS in series.


Best regards,
Vivek Alaparthi

 

If it were just one LED on a 5V supply, I'd say start with 330 ohms and see how it looks. I don't know. Maybe 1K is right, but it would depend on what's actually in the LCD unit and what your lighting conditions are. You're the designer--what does the project need?