FLEX Electronics Update 2
A brief update on V0.2:
The buck-boost converter is working beautifully! The LED driver was tested driving at two current modes 500mA (180 Lumens) and 2A (630 Lumens) over the full range of operating voltages (2.8-4.2V). There was almost no variance in current output, which means this driver will guarantee constant brightness over the entire battery life. V0.3 will have the current set at 350mA (100 Lumens) and 1.8A (500 Lumens).
The Buck-Boost driver has an enable line which enables/disables the driver and puts into a low current standby mode. This enable line can be PWM'd effectively to vary the current from 0-100% of each of the two settings (200Hz-2kHz). This proved to be very effective and there is no noticeable flicker even when driving it as low as 3 Lumens @200Hz!
As Christian mentioned in UPDATE #27 V0.3 of the electronics is in the works and more to come about that in the near future!!
Terry @ Hexbright.com
So to head off a few questions...
1) Why limit it to 1.8A instead of 2A?
A: Even at 1.8A the Buck-Boost driver has to mitigate tremendous amounts of heat through the circuit board. V0.3 will have a highly optimized heat transfer path for the Boost Converter. Proving the circuit at higher than design conditions incorporates a factor of safety into the design.
2) PWM only up to 2kHz?? Why not 20kHz??
A: There is a minimum time in which the boost converter needs to stabilize. This is not an issue however because even most sensitive of eyes cannot visibly detect flicker outside of 75hz. FYI.. most TV's update at 24-60hZ!! See the image below.