How to power a UV-C LED

[Kevin Reynolds]

I'm a chemist not an engineer and imagine this must a really basic problem but I'm a complete newbie.
I'm trying to light a UVC LED, with 6.5V forward voltage and 200mA forward current.
I connected to a 30 V benchtop power supply set to 6.5V but nothing happens.
As i missing something fundamental here? All help appreciated.
https://docs.rs-online.com/86f6/A700000006912426.pdf

 

[bertus]

Hello,

Be carefull with UV light.
It can be harmfull to humans:
https://www.safety.rochester.edu/ih/uvlight.html

Keep in mind that leds are current driven elements and not controlled by a voltage.
Does the power supply have a current limiting setting?
if so, set it at about 200 mA.
The voltage setting may be set higher as the 6.5 Volts.
Keep the cooling of the led in mind.

Bertus

 

[Harald Kapp]

nothing happens.

How do you know?
You won't be able to see the deep UV light. Measure the current as an indirect indicator of the LED's function.
Note that you cannot operate an LED on a voltage source alone without current limiting. It will easily go into thermal runaway and burn. The method proposed by @bertus is a good way to protect the LED. Read our resource on LEDs for more detailed information why and how to limit LED current.
At 6.5 V and 200 mA the power dissipation of the LED is 1.3 W. Cooling as also suggested by @bertus is required. Large solder pads (see the datasheet for recommendations) may suffice.

 

[Kevin Reynolds]

As it is now its not emitting - checked with UV sensor and also no fluorescence when placing white paper on top and not seeing a blue glow.
Not sure if my power supply is current limiting - will check today.
Ultimately i want to get to a simple set up with a phone charger type plug in power supply; the samples are to be tested at a university.
Is there an off the shelf plug in device that i could connect to an make it glow?

 

[Kevin Reynolds]

Thanks by the way.

 

[Harald Kapp]

As it is now its not emitting - checked with UV sensor and also no fluorescence when placing white paper on top and not seeing a blue glow.

I assume you are aware that an LED needs to be supplied with the correct polarity, unlike an incandescant lamp - of course you are
Chances are that you destroyed the LED in your first attempt without proper current limiting (either by the power supply or by a (nonexistent) series resistor. An LED will draw a very high current when not limited and this will easily burn the chip.

Is there an off the shelf plug in device that i could connect to an make it glow?

Not totally off the shelf, but easy to build from these components:

• DC-DC step-up converter e.g. one like this
• Current limiting resistor. E.g. when setting up the DC-DC converter to 7 V, the current limiting resistor needs to drop 500 mV at 200 mA which results in 2.5 Ω, 0.1 W (250 mW would be a good choice). Read the resource I linked in post #3 for details how to apply the resistor.
• A micro USB breakout adapter (example) as input from a USB charger (wall wart) to the DC-DC converter

You will need a case to put these things in and probably a pair of screw terminals or similar to contact the LEDs to the output of the DC-DC converter plus resistor circuit.

Of course, you can forgo the DC-DC converter by using an adjustable power supply.

 

[Emesine]

I'm a chemist not an engineer and imagine this must a really basic problem but I'm a complete newbie.
I'm trying to light a UVC LED, with 6.5V forward voltage and 200mA forward current.
I connected to a 30 V benchtop power supply set to 6.5V but nothing happens.
As i missing something fundamental here? All help appreciated.
https://docs.rs-online.com/86f6/A700000006912426.pdf

Agree with everyone that you probably burned out your led as soon as you plugged it in. Also that you need a good heat sink. 1.3 watts will need about 1.3 square inches of metal to radiate the heat produced. Hopefully the LED is mounted on a "star" base already? If so just attach the star base to some aluminum with thermal epoxy or paste (aluminum channel works well) and you're good to go. You might try this device:

https://www.ledsupply.com/led-drivers/boostpuck-dc-boost-led-driver

It will boost your 5V from the USB power supply so that the voltage is appropriate for your LED. Off the shelf, can control it with just a few resistors.

Be careful, though, the voltage difference between the input (5V) and output (6.5 or there-abouts) might be too small for the boost system. These systems are very touchy. Would work better with a higher voltage output.

Also not the rated current is 350 mA, you'll have adjust the current output DOWN to have it work properly. Just takes a resistor across two prongs on the boost puck.

I would wire TWO of your UVC emitters in SERIES (for a total voltage of 13V). Then run 200 mA through them with a boost puck. Should work beautifully, and all you have to do is connect stuff together with a few resistors. Will pull about 611mA from your usb power supply.

Andrew

 

[bertus]

Hello,

@Emesine , The shown buck regulator is not suitable for the TS used leds.
The leds of the TS have an absolute maximum current of 250 mA.
The buck you showed is for 350 mA.

Bertus

 

[Emesine]

I'm a chemist not an engineer and imagine this must a really basic problem but I'm a complete newbie.
I'm trying to light a UVC LED, with 6.5V forward voltage and 200mA forward current.
I connected to a 30 V benchtop power supply set to 6.5V but nothing happens.
As i missing something fundamental here? All help appreciated.
https://docs.rs-online.com/86f6/A700000006912426.pdf

As Bertus points out- the Boost Puck is rated to 350 mA, which would fry your LEDs. He is right, it would ideal to use a driver that isn't capable of destroying the emitter.

However, the unit can be trimmed down very easily with a resistor across the "control" and "reference" pins on the device. With the proper resistor in place you can set the device output to your desired 200 mA ( or lower if you prefer). Just keep in mind, as Bertus pointed out, that if you don't have the resistor in place, of if you don't pick the correct value, then it will blow your leds.

Just my thoughts- I like the device because it is super user friendly. Pins are large and easy to solder to. I used to use these on LED lights when I knew next to nothing about electronics.

Good luck!

Andrew

 

[bertus]

Hello,

You can also use this simple constant current circuit:


Bertus