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UV LED Boards with Blue LEDs

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I need to have 8 3/4" or 1"W x 28"L rigid LED strips made. I would like 1 high intensity/power LED per inch for a total of 28 LEDs spaced out evenly (Jupiter, Rigel 1watt?). Now for the LEDs themselves I will need two types. Blue LEDs at 460nm range and UV-B LEDs at 310nm range. The beam angle I would like is 30 degrees. I need the LEDs to alternate, 1 blue, 1 UV-B, 1 blue, 1 UV-B and so on. I would like four (4) of the strips to start with a blue LED and the other 4 strips to start with a UV-B LED.

I would like to try and avoid 8 separate plugs. I would like 4 strips linked together to 1 plug/adapter. The strips need to alternate from each other though. So 1 strip that has a blue starting bulb and then the next strip that has a UV-B starting bulb. Basically what I am trying to say is that the same color should not be side-by-side between the two strips. So I would need the 8 total strips split up into groups of 4. Each group should contain 2 LED strips that start with a blue diode and 2 LED strips that start with a UV-B diode. Wire those 4 strips together into 1 120v plug or 12v adapter. Or would a 24v be better? Would I even need a 24v? I have no idea on this part, but just so you know these strips are going to be plugged into a wall.

The 4 strips wired together are going to be spaced about 3 inches apart from each other so they do need enough slack in the wire so they can be mounted properly. Which reminds me; there will have to a place where a screw can mount them into place without damaging the board. The spacing for the screws should be every 7 inches. And then the wires from each strip just has to tie into 1 plug.

I did some poking around for the UV-B LEDs I am looking for. I found a company called Seoul Optodevice Co.,Ltd. They produce what they call BioUV 310nm LEDs.

So, if this can indeed be done for me I guess I need to know approximate costs for this type of work. I am hoping this should be fairly simple in terms of construction. It is just a matter of getting those UV-B LEDs in that 310nm range. I am not so sure how readily available they are. Anyway, I look forward to what you guys have to say about it. Thank you

Power Dissipation from 1 Watt LEDs

Assuming you choose to power the LEDs at one watt, you will dissipate 28 total watts of energy. This may require some advanced thermal management, as a standard circuit board will make this more difficult. An aluminum board can provide better thermal transfer properties. For an even lower junction temperature, a finned heat sink can be added to the rear side of the LED board. Nichia tests for lumen maintenance at 90 degrees Celsius, so it would be wise not to exceed this limit. However, an even lower junction temperature is obviously better yet.

310nm UV LEDs

The UV 310nm LED will be somewhat difficult to source, assuming the specifications for beam angle and power rating provided. Even if someone produced an LED with a wavelength this low and a beam angle this narrow, it would be extremely expensive, and dangerous to the human eyes. Nichia currently offers a surface mount LED rated at 310nm peak wavelength, and 270nm on the low end. This only applied from the P7 rank, so you may have to accept other ranks as well. The P9 rank goes up to 390nm. Seoul also offers several UV LEDs that may work well in this application.

Optics for Nichia UV LED

The Nichia SMT UV LED features a full beam angle many times wider than 30 degrees. To achieve this narrow angle, you will certainly require a secondary optic. The optic will attached to the top surface of the LED, which will focus your beam into the narrow pattern required. A custom designed and manufactured optic may be necessary if an off-the-shelf version is not offered.

Alternating Blue and UV LEDs

Alternating between blue and UV LEDs should not be difficult. There are two basic ways to configure the LED circuits. One way is to break them out into two separate circuit channels, allowing for independent operation of blue, UV or both. The second way would be to simply interconnect the blue and UV LEDs in series. This would allow them to operate together, and would not provide the flexibility of unique color combinations.

For method one, two main wires may connect back into a microcontroller responsible for activating the circuit. One wire for blues, another for UVs. The most obvious configuration would include a MOSFET configured an a low-side driver, connected to the cathodes of the LEDs. There would be one MOSFET for blue, and another for UV. The two signal wires will connect from the gate back to the LED controller. On the high side, a constant current source is highly preferred. A resistor would not perform well in this circuit due to the amount of current.

The later method may also include a switching transistor if precise control, such as dimming, was required. In this configuration, the blue LEDs and UV LEDs can be connected in series. If single color options are not required, the circuit would not have to be broken out into sub-colors. The constant current source is still critical.

Since you require a special pattern that alternates between blue and UV, you will require at least two unique configurations during the SMT assembly process. One will start the board off from a blue LED, and the other from a UV-B LED. The only downside here is that your assembly costs will probably increase due to this special assembly process.

Powering LED Strips

Branching power to the LED strips should be easy. As long as your main power supply can source sufficient current, there is no reason why a simple power bus configuration would not work. Simply run the power and ground leads from the main power source out to each of the four LED strips. Make sure the jumper wires are rated for the total amperage of the system, and also avoid excess wire lengths. Longer wires can result in unwanted resistance, and thus lead to voltage drops across the line.

Voltage for Blue and UV LEDs

A 24 volt power supply should be slightly more efficient than a 12 volt power supply. This is because you can configure more LEDs in series using a higher voltage, which means that you require fewer number of LED drivers. Fewer drivers not only results in less heat dissipation, but also reduced cost. The disadvantage is reduced redundancy. Using the higher voltage, you have half the total number of circuits, but almost the same total number of components. Chance of circuit failure is almost the same, but now you loose twice as many LEDs if and when this occurs. At any rate, it is not likely that an LED circuit would fail unless resulting from defective parts, poor design, poor assembly, or an unfavorable operation condition.

LED Project Costs

The major production costs associated with this design will certainly be the UV LEDs, since they are by far the most expensive LEDs on the market. Some may cost in excess of $50.00 each, even in volume. Another problem associated with UV LEDs is that they tend to have much shorter life expectancies, compared to many white or blue LEDs. The costs associated with a custom design work may range up to several thousand dollars or so, depending on the number of prototypes required. Our Free Design Support program allows you to progress through the design free of cost, but does not include items such as schematic capture, board layout, prototyping, or bench testing.