Blue shark's minimum voltage input below Led

What is the absolute minimum voltage difference required below the battery output and the led forward voltage for the blue shark converter board to stay in boost mode and not direct drive and burn up.

Ie, how accurate / sensitive is it?

Related to this, I want to run a dual MC-E setup, each in series, then tied parallel. I want to use an 11.1v li-ion battery. It has a full charge rating of 12.6v. I'm worried about low power modes, roughly 250mah-300mah modes when the LEDs are rated to around 3.15v. That will give me a forward voltage equal to the battery voltage. Will I have issues?

http://www.cree.com/products/pdf/XLampMC-E.pdf

Hey dude you hijacking my thread? LOL...

Are you running a shark board which is boost ONLY? If we only knew by how much though?

The Shark like most boost converters will stop boosting when the input voltage equals the output voltage. After that the converter stops and all current flows from input to output through the boost diode.

When this occurs you have the battery directly connected to the LEDs and the current to the LEDs will be dependant on the Vf curve of the LEDs.

This may limit how low you can drive the LEDs with a boost converter if in DD the LEDs are drawing 300mA. That would put 300mA as the lowest you could go with or without a converter board.

As long as the battery range is always lower than the Vf of the LEDs you are in good shape.

The minimum below LED is 0 Volts. It's usually viewed the other way around in terms of how high or close to Vf you can get before the Shark is no longer boosting. Either way it is 0V if I understand correctly your question.

Wayne

gav6280 said:

Hey dude you hijacking my thread? LOL...

Are you running a shark board which is boost ONLY? If we only knew by how much though?

Click to expand...

Sorry for the hijack. It was an accident?

OP: There is no minimum, it is the maximum current. For example, you have a 5V source and 4 LED's at 1A with a Vf of 4V, which is 12V. The shark must take the 5V and draw enough current to output 1A at 16V, which would be 3.84A at 5V assuming 20% driver inefficiency*. IIRC, 4A is the absolute maximum that the shark can handle (so in other words, this setup would work, but barely), Wayne, can you confirm or deny this?

And yes, I made up 20% inefficiency as a worst case, I'm not sure of the real numbers.

*If you're running it this hard, you're dropping about 4W in heat, so you need your heatsinking sorted!