Constant Current Driver For Deep UV\UV-C LEDs - Page 1
Forum section: electronics / projects

author: KJ-90
author_rank: Contributor
timestamp: December 20, 2016, 01:20:17 am
content: I was wondering if anyone knows of a driver circuit specifically designed for deep UV\UV-C LEDs. These very expensive devices have a forward voltage of about 6.5 - 8.0 Vdc, with a forward current of a few hundred mA.

author: georges80
author_rank: Frequent Contributor
timestamp: December 20, 2016, 01:41:42 am
content: Constant current is constant current...You just need a constant current LED driver that runs at the drive current you desire. Regardless of whether your UV led is 'expensive' or not, it just needs constant current - nothing 'special'.At the most you may have thermal monitoring to roll output current back if the LED/heatsink gets too hot - but that's no different than any other LED.You would need to specify a lot more regarding what driver you need. You make no mention of input voltage range or specific drive current or whether you need to adjust output current or provide PWM etc. The devil is in the details...cheers,george.

author: KJ-90
author_rank: Contributor
timestamp: December 20, 2016, 11:05:19 pm
content: I'm sorry I forgot to publish detailed LED technical data, since georges80 was asking about that. The LED in question would be a SETi"UVCLEAN265-3" ( capitals used only for part number, not shouting here ). The device has detailed technical data at:www.qphotonics.com/Deep-UV-LED-lamp-1-3mW-265nm.html. As we can see from the data sheet, the typical Vf is 6.5 volts ( maximum of 8 Volts ), with a typical If of 60mA and an absolute maximum of 80mA. The basic problem with driving this type of LED is the fact that the If has to be very tightly and reliably controlled, due to the very high cost of the device ( about $365 US ). The device actually costs dozens of times more than the circuitry necessary to operate it. Deep UV LEDs are very easily destroyed by excessive If- as you can see from the data sheet, the absolute maximum If ( 80mA ) is only 20mA above the safe If. This means that current sensing should also be done right at the LED terminals. Voltage sensing is not difficult, using an MC3423 connected to the LED terminals, with the 3423 overvoltage trip connected to a tiny solid state relay in series with the LED. Should the voltage go too high ( e.g. 7.5 V ), the 3423 will trip the SSR, protecting the LED. The SSR can also be turned off from a redundant current limiting circuit.Even if one used hi-rel components for the constant current driver, a redundant overcurrent trip is needed for the LED because of its very high cost. Readers can assume the LED driving circuit would be powered by 12 V, and the diode runs in CW mode only ( no PWM ). Unfortunately, very few deep UV LEDs have internal photodiodes to monitor output power ( like laser diodes ). Otherwise, onecould probably use a modified laser diode driver circuit. If I recall correctly, when I was in high school in the early 2000s, the first UV LED made by Nichia actually had an internal photodiode, and the company recommended it be run like a laser diode.

author: Benta
author_rank: Super Contributor
timestamp: December 20, 2016, 11:40:23 pm
content: Quite frankly, driving the LED at the correct current is trivial.I see a much bigger issue after looking at the link you provided, which is thermal management. The specifications are listed at 25 C, which I suspect is case temperature.You'll really need to look at chip temperature and thermal resistance first before you can design reliably.Benta.