How to operate four blue OSTARs LE B S2W

I want to built an underwater (scuba) fluorescence lamp with blue light for research. I received 2 Blue Sharks and have the following conditions.
1. Akku 12 Volt, 9 Ah
2. 4 pieces SMT (blue, 4-chip) OSTAR LE B S2W
OSRAM Semiconductors provided these SMTs unmounted. Since I have no possibility to fix them by reflow, I asked them to mount them on a board comparable to the white OSTARs (same star design as LUXEON). Unfortunately they prepared them in parallel way rather than serial. Instead only 1 Plus and one Minus in the Standard OSTARs, I have 4 Plus and 1 Minus. Every sub LED in the 4-LED-Chip has a separate red wire (plus) and all a common minus(black). I expected serial connection of the 4 LEDs in the 4-Chip-Type (forward voltage around 4 x 3,5 >14 Volt, 700 mA).
In this case I could operate two 4-Chip OSTARs with one Blue Shark (around 28 Volt).
Since my knowledge in electronics is pure, I have the following question:
How can I operate 4 pieces of parallel wired OSTARs LE B S2W (4-Chip-LEDs) on my 12 V Akku?
I would be thankful for suggestions.

Hate to say this, but you're not going to be able to use the Blue Sharks for that, looks like you're going to have to get a Shark Buck instead, given that you're now looking for an output of around 3.5 V at 2.8 A. I think this one is the one you'd be looking for.

Thank you so much for the quick answer. I also have contacted OSRAM. In the case that they will donate serial OSTARs, I think I could use the Blue Sharks. Otherwise with the "parallels" in my hands, I will follow your suggestion.

One more question. So I need for my 4 pieces 4-Chip-OSTARs a total amount of four Shark Buck 3 A with maximum output configuration of 3 Amp each. Would be happy about your comment.

I think you could get away with using only two Shark Bucks by putting two of the Ostars in series with each other to create two strings that will require ~7V at 2.8 amps, then drive each string with a Shark Buck.

That said, I'd prefer if a more experienced member would chip in with his/her views on this.

Thank you for this excellent recommendation and help. Please let me know that I understood you right. I can use my Akku 12 V, 9 Ah and follow your advice. Under these conditions every sub-chip of the two 4-chip-OSTARs (i.e. total number 8) get 3.5 Volt and 700 mA?
The same arrangement I will perform with the two other 4-chip-OSTARs. So I need two Shark Bucks for my lamp only.
Would be nice if you could confirm my a little bit stupid questions. Regards Horst

If you wire the two Ostars in series then the Vf would be 3.5V + 3.5V or 7V. This can be driven with one Shark Buck as long as you keep the battery voltage a couple volts higher than 7V. Two drivers each driving two Ostars.

Wayne

Thank you very much indeed. Your information helps me a lot. If OSRAM offers no other approach (cheaper) I will order two Shark Bucks (3 Amp).
Best wishes
Horst

Hi Wayne,

I have alreday ordered two Blue Bucks with 3 Amp.
The mechanical parts of my fluorescence lamp are finished. Now I have found out that in 3 Ostars one of the four chips each is not working.The forward current of the SMTs is maximum 1000 mA. Do you think I could operate the remaining 3 chips (in a string instead of 8 now 6 only) with one Blue Buck. The result would be 7.5 Volt at the Buck with 3 Amp. Is this correct?

Thank you in advance for your comments.

Regards

Horst

horstartur said:

Hi Wayne,

I have alreday ordered two Blue Bucks with 3 Amp.
The mechanical parts of my fluorescence lamp are finished. Now I have found out that in 3 Ostars one of the four chips each is not working.The forward current of the SMTs is maximum 1000 mA. Do you think I could operate the remaining 3 chips (in a string instead of 8 now 6 only) with one Blue Buck. The result would be 7.5 Volt at the Buck with 3 Amp. Is this correct?

Thank you in advance for your comments.

Regards

Horst

Click to expand...

If you ordered Blue Sharks they are boost mode converters. If you ordered Shark Buck 3A then those are buck mode converters.

If only three of the 4 dies are working and the Vf is only 3 * ~3.5V then you will have no problems driving 3 die with one Shark Buck.

If one of the die has gone caput I would suspect something is not correct. Is it possible that the LED is not thermally mounted correct. Did the one die during usage? If so, you might want to double check the LED mounting and or redo them to ensure a good thermal path to the heatsink.

Wayne

Thank you very much for the quick reply. So I will operate two SMTs (with 3 Chips each) in series with a Shark Buck (3 Amp) resulting in 7 Volt, 3 Amp.

Regards

Horst

Hi Wayne,

I just received the two Shark Bucks with 3 Amp. I am a little bit confused. In the foto the LED + (output) is shown in the center of the buck, the LED- at the rimb. The LED+ gives Minus in the voltmeter and has connection to the heatsink(ground). The LED(-) gives plus in the voltmeter. I already wondered, why the LED+ is so closely located to the heatsink at the backside. I soldered very carefully under the stero microscope that there is no contact between LED+ and the heat sink (ground). On the other hand LED- , ground and Vin are very easy to connect with wires without risk to come in contact to other parts.
When I connect the LED- to the Plus and the LED+ to the Minus of the voltmeter (the correct connection LED+ to Plus and LED- to Minus gives me a negative value) it shows me the value of my akku > 12.5 Volt. However the OSTAR (SMT) shows no reaction.
I also measured the untreated other buck > there is also a connection between LED+ and heatsink (ground).
What is wrong?

Hi everybody,

Wayne is perhaps very busy or in holidays. Therefore my question to the community. I received two Shark Bucks (3A). I found out that the LED+ (Plus) has contact to the ground and Copper C. I did not make any soldering that I create problems by heat or an artifical bridge.
Did also somebody else have similar problems with Bucks? I found out that Wayne offered in several cases replacement of the bad (defective) Shark Bucks.
Please let me know your experience. For my stupid understanding: VIn must be connected with Plus of the source. Ground with Minus of the source. Of course LED+ to the positive In of the LED and LED- to the negative entrance of the LED.
Thanks in advance Regards Horst

Hi, were you find the blue Ostar?

I received them for scientific tests directly from OSRAM.

Regards

Horst

Thanks, remember post photos where you are done... Good luck...