Hello All.

Newbie here.
I am working with 4 high power Cree leds. I need recommendations on a constant-current power.
Notes:
1. 4x Green XP-E2 LED [ Max Drive Current: Up to 1000mA / probably run them at 350ma / FWD v 3.2 (3.7 max) at 350mA)
2. Power supply input @ 120v
3. Needs to be dimmable via PWM.

I am really not sure what to get.
Any help?
Thank you for your time.

 

OK, so if you want to have dimming control of the the four at the same time, you can put them in series and use a variable 12 volt one amp switcher power supply Start with the voltage lower and adjust it up until they draw the 350 milliamps. If the supply is fairly stable you would not even need a series resistor.

 

Hello All.

Newbie here.
I am working with 4 high power Cree leds. I need recommendations on a constant-current power.
Notes:
1. 4x Green XP-E2 LED [ Max Drive Current: Up to 1000mA / probably run them at 350ma / FWD v 3.2 (3.7 max) at 350mA)
2. Power supply input @ 120v
3. Needs to be dimmable via PWM.

I am really not sure what to get.
Any help?
Thank you for your time.

Suggest this, all LEDs wired in series.
Power Supply

 

A constant current supply as @sghioto suggested would be the most reliable solution.

 

OK, so if you want to have dimming control of the the four at the same time, you can put them in series and use a variable 12 volt one amp switcher power supply Start with the voltage lower and adjust it up until they draw the 350 milliamps. If the supply is fairly stable you would not even need a series resistor.

For four green LEDs in series, the total Vf can vary between 10.8 and 13 V, so a simple 12 V switcher might not have a wide enough output voltage adjustment range to cut it.

LED Vf has a significant temperature coefficient. If you dangle-bias the LEDs to 350 mA when power is applied, the current through them minutes / hours later will increase as the Vf decreases. The combined Vf value can change by almost 300 mV over a 60 degree temperature change (25C cold/characterization temperature to 85C operating temperature). With a fixed-output-voltage power source, this is a possible thermal runaway situation.

I recommend shopping on amazon or ebay for a true constant current LED power source, one with a compliance range of at least 9 V to 15 V.

ak

 

Thank you for the additional information and recommendations- I will check them out.
I left out a couple of details:
1. They will be wired in series.
2. The four will be dimmed collectively- not individually.
3. Indoor
4. It is for a photo enlarger. Exposures are only on for about 5-20 seconds [LEDs on]. About 5-10 minutes between exposures [LED off].
5. Most of the time, LEDs will be dimmed. Don't need full power- I think.

 

OK, yes, I know that the forward voltage changes with temperature. Some power supplies also include a current limit function.

Besides that, these LEDs are rated for 1000 mA max, , being set to run ate only 350 mA, which means that even if the currentdoubles, they will be well within their safe area. Certainly a series resistor could be added.
BUT, for the application described in post #6, there should be no problems. AND the TS also mentions dimming by PWM. But with an adjustable power supply will that be required???