Red Green Led 2 Leg

[EdW]

I have a circuit that changes polarity and it is in range of 6 to 12 dc. What would be a simple circuit so I could limit the voltage to use this led 3.3v light up red an green .
Thanks

 

[(*steve*)]

Place a 470Ω resistor in series with the LED.

 

[Audioguru]

3.3V is probably the green forward voltage and the red will be about 1.8V to 2.2V.
Use a single resistor to ground that is (12V - 1.8V)/20mA= 510 ohms or more. The resistor will dissipate (heat) with 0.2W so use a half-watt resistor.

 

[EdW]

The led is green when + - and red when - + and the voltage is variable at times.

 

[(*steve*)]

The led is green when + - and red when - + and the voltage is variable at times.

Yes, we know

 

[EdW]

Yes, we know

Even with the voltage can be anywhere from 6 to 20v a one size res will work.

 

[(*steve*)]

Yes it will. The brightness will vary, but the LED will be safe.

Does the variation in brightness concern you?

 

[EdW]

Yes it will. The brightness will vary, but the LED will be safe.

Does the variation in brightness concern you?

Yes it will. The brightness will vary, but the LED will be safe.

Does the variation in brightness concern you?

You say res on ground side. Polarity is changing all the time. And how could I use a 5v regulator with the polarity changing every few minutes?

 

[(*steve*)]

The resistor can be on either side of the LED, it doesn't matter.

The following circuit will limit the LED current to 10mA for an input voltage between +/-6V and probably +/-30V.

To operate correctly at 6V the diodes should be Schottky diodes.



Sorry about the quality.

Edit: transistors can be BC548 or similar.

 

[EdW]

The resistor can be on either side of the LED, it doesn't matter.

The following circuit will limit the LED current to 10mA for an input voltage between +/-6V and probably +/-30V.

To operate correctly at 6V the diodes should be Schottky diodes. I can't find 6v Schottky do you mean zener?

View attachment 31812

Sorry about the quality.

Edit: transistors can be BC548 or similar.

Are you saying to just use a 6v Schottky. I can't find 6v Schotty do you mead zener?

 

[(*steve*)]

No, I mean the 4 diodes shown on that circuit need at be Schottky diodes.

Having them rated for maybe twice the max input voltage would be safe. In this case 20V or more would be fine.

 

[EdW]

No, I mean the 4 diodes shown on that circuit need at be Schottky diodes.

Having them rated for maybe twice the max input voltage would be safe. In this case 20V or more would be fine.

Thanks