Andy1845c
Active Member
Any input or comments are welcome
I want to use some 3w luxeon LEDs in a project. Their max forward current is 700mA, but I was thinking of running them at somthing closer to 500 mA.
I want to use 4 of them in series on truck with a 12v system. I am figuring a voltage of 13.8 when the engine is running and 12v or just below with the engine off.
Typical Vf is 2.2v * 4 = 8.8
13.8 - 8.8 = 5v
5v/.500 = 10Ω
.500 * 5 = 2.5 watts
I know this would waste power, but its not a huge concern.
I was going to go with 5 or 10 watt resistors. I have a bit of room to mount them. The duty cycle is also not 100%, so I don't think the heat would be a huge problem.
My other idea is to use an LM317 as a constant current supply.
The reason I am at this point leaning toward the resistors is less parts = more reliable.
Also, would it be smart to add a diode inline with the luxeons to protect them from any reverse polarity spikes?
I want to use some 3w luxeon LEDs in a project. Their max forward current is 700mA, but I was thinking of running them at somthing closer to 500 mA.
I want to use 4 of them in series on truck with a 12v system. I am figuring a voltage of 13.8 when the engine is running and 12v or just below with the engine off.
Typical Vf is 2.2v * 4 = 8.8
13.8 - 8.8 = 5v
5v/.500 = 10Ω
.500 * 5 = 2.5 watts
I know this would waste power, but its not a huge concern.
I was going to go with 5 or 10 watt resistors. I have a bit of room to mount them. The duty cycle is also not 100%, so I don't think the heat would be a huge problem.
My other idea is to use an LM317 as a constant current supply.
The reason I am at this point leaning toward the resistors is less parts = more reliable.
Also, would it be smart to add a diode inline with the luxeons to protect them from any reverse polarity spikes?