Most of you know or are familiar with the Shark and Blue Shark.
We are adding to the family the Shark Buck a step down converter based on the same IC used in the Shark and Blue Shark.
The Shark Buck is the same diameter (0.75") as the other two, has the same trim pot and trim pot functionality. I Remora can be mounted on the Shark Buck and behave the same as the regular Shark (Note 1).
Since the control trim pot functions the same as a regular Shark you can use one external pot to control both the Shark and Shark Buck. Thus, one external pot or one Remora could control two Blue Sharks and one Shark Buck to drive two strings of 4 single LEDs in series and the Shark Buck could drive one Seoul P7 or one Cree MC-E LED. Many other combinations can be had with this versatile common control interface.
Since the Shark Buck steps down the output current max is greater than in a boost configuration. I have tested the Shark Buck with 3A to the load and it behaves nicely.
Here are some numbers I graphed from a Revision 1 board.
Vin Iin Vout Iout (Watts) (Watts) %
15 0.95 3.635 3.037 14.1455 11.0395 78.0%
14 1.03 3.523 3.053 14.3067 10.75572 75.2%
13 1.11 3.516 3.063 14.3079 10.76951 75.3%
12 1.2 3.509 3.073 14.268 10.78316 75.6%
11 1.31 3.504 3.087 14.2659 10.81685 75.8%
10 1.45 3.499 3.105 14.3405 10.8644 75.8%
9 1.62 3.497 3.122 14.4018 10.91763 75.8%
8 1.83 3.495 3.14 14.4387 10.9743 76.0%
7 2.082 3.489 3.153 14.34498 11.00082 76.7%
6 2.439 3.48 3.154 14.36571 10.97592 76.4%
5 2.74 3.453 2.999 13.3986 10.35555 77.3%
I may have an error at the 15V input as the efficiency rose when it should have continued the downward slope. The line should be straighter, but, I believe this is due to the time it takes for me to read and write the measurements down the board and LED temperature moved and made for a slight error in measurement. If you straighten out the line you can see that around 5V the efficiency is just over 79% and at 14 Volts it has dropped to around 77% efficiency. I would draw a straight line from these two to get a more realistic graph of efficiency.
Note in the numbers that the current to the LED was slightly higher than 3A. Unlike other converter boards this one is delivering 3A.
The Shark Buck also has reverse battery protection and accomdates the same copper C as on the regular Shark for optimum thermal transfer to the heat sink.
There are two sense resistors on this board making it easier to generate a valid output current combination.
One 0.1 ohm resistor = 1A max.
Two 0.1 ohm resistors = 2A max.
One 0.1 ohm, one 0.05 ohm = 3A max. (maximum output configuration)
I'm sure you have questions and feel free to post them here in this thread. When I get more pictures and data I will add them to this thread.
1) The inductor placement encroaches into the area under the Remora and raises the height of the Remora. Once mounted the completed assembly will be thicker than a regular Shark + Remora.
Shark Bucks can not be paralleled for more output current.