Circuit in Cygolite tail light

[LEDPowered]

The Cygolite 2W tail light has a 2W LED and can run for 300 h on a single recharge. I can't understand how this is possible. The power source in the taillight is most likely a 3.7 V Li-ion cell. It is being used to run a led with a Vf of 2.4 V odd. Is there any way to achieve a voltage drop without wasting energy on a resistor or IC. Could anyone recommend a source where I can learn to do the same using capacitors, transistors and the alike. I want to make the most of power stored in my cell and use as much of it to power the LED rather than waste it as heat on components other than the LED. Has anyone taken apart the Cygolite taillight to see what is the circuit they have used. Thanks a lot in advance for your help.

 

[znomit]

The Cygolite 2W tail light has a 2W LED and can run for 300 h on a single recharge.

Welcome to CPF LEDPowered :welcome:

Its a 2W LED. Its doesn't mean its running at 2W in this light.
A good LED driver will step the voltage down(or up) from the battery to the LED, keeping a constant current to the LED, and can hit > 90% efficiency. A poor one will just burn off the excess voltage on the way to the LED and dim as the battery voltage drops. Here you're looking at 2.4V/3.7V so around a third of the power is lost.
A lot of lights are not properly regulated so will dim considerably as the battery runs down. You might find the acceptable brightness is only achieved for a small fraction of the runtime.

For off the shelf, high quality LED drivers for bike lights I use Taskled:
http://www.taskled.com

 

[Flamingtaco]

300hr runtime is for the most efficient flashing mode (which ever one give the LED's the most off time). Full on is listed as 4.5hr for the current Hotshot 2W USB. Easy to get 300hr run time when you are only flashing the LED's, especially when some 5mm LED's ones are getting a lot more live time than the 2W banger.

2W LED's range between approximately 2.2 and 3.4V, IIRC. A sub 3V LED would save them from making a boost circuit, so maybe they saved a penny.

Most LED design efficiency comes in selecting a battery that maintains a flat discharge voltage for most of a cycle not too far above the max voltage required to drive the LED at the desired max current while taking into account voltage losses that will occur in your driver circuit. Many regulating circuit packages are close enough to each other in efficiencies as to not matter, you're primarily dealing with selecting function vs cost.

The cost of building a discrete component LED driver circuit does not pay off, so you must do it for fun, with no expectation. The reality of an IC chip is that it is made up of all those same discrete electronic components you mentioned... resistors, capacitors, inductors, transistors, etc. However, it was designed by people that know the crap out of electronic design, and will be more efficient than discrete components, even if you could mimic the internal layout.

They've already got a lot of tech in those itty-bitty high power blinkers, the typical 4-6 hours of runtime on full on blind mode is amazing considering the size of the batteries, and being USB rechargeable is just sweet, sweet icing. If you want to fiddle with rear lighting, I would suggest building from scratch a system that illuminates well in a 180º or greater arc. Cygo, Niterider, et. al. have a good bead on the approaching from behind issue dealt with by the rear blinkies. If you really want to fiddle with the cygo... I would shoot for uprading the LED to a more efficient 2W'er if available, and/or attaching an additional battery for extended run time.

Good luck!