Small bi-color LED circuit

Thread Starter

Teq

Joined May 19, 2007
2
I'm not an electronics expert by any means (about 6 months experience 14 years ago), so would like a little help with a project I am working on.

I am trying to power a bi-color LED from a 5 volt supply, in the 0 state this should glow red, when 1 blue. (red having 2.1 and blue having 3.3 forward voltages), I've thought of a not gate circuit but am not sure if this will work properly for my means. (if you do come up with a solution a resister ohms value, any diode and transister models that would fit into the project would also be helpful).
 

Papabravo

Joined Feb 24, 2006
12,301
I'm not an electronics expert by any means (about 6 months experience 14 years ago), so would like a little help with a project I am working on.

I am trying to power a bi-color LED from a 5 volt supply, in the 0 state this should glow red, when 1 blue. (red having 2.1 and blue having 3.3 forward voltages), I've thought of a not gate circuit but am not sure if this will work properly for my means. (if you do come up with a solution a resister ohms value, any diode and transister models that would fit into the project would also be helpful).
Is this a two lead or a three lead bicolor?
 

hgmjr

Joined Jan 28, 2005
9,029
A part number and manufacturer's name for the LED you are using would also help us in providing you guidance.

hgmjr
 

bloguetronica

Joined Apr 27, 2007
1,359
It seems to me that it is a bicolor led that glows green when biased in one direction and red on the other. If that is the case, nothing better than a H-bridge with transistors, like the ones used to drive a bidirectional motor.
 

Papabravo

Joined Feb 24, 2006
12,301
Some bicolor LEDs are RED/GREEN, but not all. He might have a RED/BLUE bicolor and the problem is more complex than you might think. Because the BLUE LED has a much higher forward voltage, the resistor you would compute for the RED half would not allow sufficient current through the BLUE half. So an H-bridge with two resistors might work
 

hgmjr

Joined Jan 28, 2005
9,029
The mystery should disappear once we get a datasheet in hand.

hgmjr
 

Thread Starter

Teq

Joined May 19, 2007
2
Sorry I didn't have the data sheet at hand. I've actually now solved my problem using a 4069 CMOS logic driver.

Just FYI the LED did have two forward voltages on a 3 pin package. Red being 2.1v, Blue 3.3v.
 

hgmjr

Joined Jan 28, 2005
9,029
I don't suppose you would be willing to post your final solution for the benefit of others who might have a similar project in mind.

hgmjr
 

Papabravo

Joined Feb 24, 2006
12,301
Sorry I didn't have the data sheet at hand. I've actually now solved my problem using a 4069 CMOS logic driver.

Just FYI the LED did have two forward voltages on a 3 pin package. Red being 2.1v, Blue 3.3v.
Danger Will Robinson. You're going to be quite disappointed in the 4069's ability to light a LED especially the BLUE one from a 5V supply. The spec sheet says you can expect less than 1mA. I guess this is OK if they are very bright and super efficient. If the 4069 does not work, may I suggest a 74AC04 which should be more than enough drive at 24 mA.
 

hgmjr

Joined Jan 28, 2005
9,029
I agree with papabravo that you will get far better results by directly driving your LEDs using a 74AC04 than you can directly driving them using a 4069B.

If you find the brightness of the LEDs is not what you were looking for, then at least you have another option.

We would still be interested in seeing your circuit diagram.

hgmjr
 
Top