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Do not understand connections to the pin K

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vivek20055

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Hi,

I am using the LCD in my project.

I could not understand connections to this K,A pin this circuit diagram.

In datasheet it is clearly given to give current to A(anode) and ground the K(cathode).

What about connections to kathode. what is going on in this circuit


Best regards,
Vivek Alaparthicircuit2.png
 

keith1200rs

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It looks like an LED backlight with two brightness levels. One transistor will turn on the LED through R9 (and R2) giving a low current. The other transistor would turn on the LED with the current limited only by R2 so it will be a lot brighter.

Keith
 

vivek20055

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It looks like an LED backlight with two brightness levels. One transistor will turn on the LED through R9 (and R2) giving a low current. The other transistor would turn on the LED with the current limited only by R2 so it will be a lot brighter.

Keith

Hello keith,


why 2 transistors for lighting LED. What happens if I directly give the source through R9 (larger value) which will allow low current and dim the LED.


Best regards,
Vivek Alaparthi
 

keith1200rs

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Vivek ,

With two transistors you get the choice of no LED, dim LED & bright LED. If you always want the LED on, but dim, then you could connect one end of R9 to ground and leave off the second transistor, as you say.

Keith
 

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