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Enable a RGB LED with a single transistor)

lax

Sep 12, 2021
3
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Sep 12, 2021
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Hi,

I tried using a single transistor to enable/disable an RGB LED (SMD) where the RGB signals are coming from a stable source. .. It did not work. Can anybody tell me what I did wrong and how to do this?
 

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Martaine2005

May 12, 2015
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First of all, you need to understand a common cathode or common anode RGB LED. Which do you have?
 

Harald Kapp

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Nov 17, 2011
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Your schematic is incomplete - at least the part you've allowed us to see.
From the schematic I take it the LED is common cathode.
I annotated your schematic with 2 questions:
1661230286236.png
Also current limiting resistors for each single LED are missing or at least are not shown.
 

lax

Sep 12, 2021
3
Joined
Sep 12, 2021
Messages
3
Your schematic is incomplete - at least the part you've allowed us to see.
From the schematic I take it the LED is common cathode.
I annotated your schematic with 2 questions:
View attachment 55962
Also current limiting resistors for each single LED are missing or at least are not shown.
Yes, the GND is correct. It's actually described on the PCB diagram. This is a connection from another board, so the signals are coming from another circuit through a Pin/header.
The issue was tracked down to the RGB part needing more than the 3.3V that the circuit is using. And I think I should have put a WAAAAY bigger resistor for the RGB_ENABLE signal.

My question was mostly f the design is sound. I think with proper voltage management, it should work.

However ... the Red LCD should still work.
Thanks for your help
 

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