LED Voltage and current question

[Richard21]

According to the above circuit I need about 6 volts input to run a luxeon star LED. As I understand it, the regulator takes about 3v leaving 3v for the LED and the constant current regulator will will provide a fixed current of 320ma which is just fine.

My question is, can I use a higher input voltage here, such as 12v without affecting the luxeon star? Although I know that the current output is fixed, will the output voltage rise as the input voltage rises and burn out the LED?

Image & circuit reference http://led.linear1.org/a-cheap-current-regulated-luxeon-star-driver-design/1/

TIA

Richard

 

[MatajumotorS]

Current will stay the same on output, voltage will be depending of led , there will be larger drop acros the regulator - more heat @ 12V input, thats all.

 

[AsianSignals]

I don't use this circuit directly, but generally speaking this type of circuit will work harder to drop the voltage down to the correct level. The output will be maintained for the LED but the voltage regulator will get hotter as it does more work. If that temp exceeds a certain level, the part will de-rate and begin to stray from the previously set output. I think you'll see a slight increase in output current in this case.

The bottom line: If you put a heatsink in the transistor then you should be able to safely increase the input voltage.

 

[Richard21]

Thanks for your replies. I was trying to establish a safe working principle here, before using the circuit for my array. The actual setup will be running about 10 LEDs in a series parallel combination. The series strings of 2 LEDs will require 2x3.4volts = 6.8v and these 5 strings will be in parallel making up the full 10 LEDs. I expect the voltage from the regulator, given a 12 volt input will be about 9v leaving a 2.2v differential to drop. Of course the Current will increase because of the extra load from the LEDs.

If you have any other (better) ideas to build a LED light bar, I would be glad to hear ... My criteria is that it must be able to run off 12v supply (car battery(s) that may fluctuate in voltage between 12 and about 14.5 (maximum charger voltage) while in use. Leds must stay at a constant brightness (ish...) and be able to stand the fluctuations.

Thanks Richard