ktmrfs wrote:
while this may solve the 14.7V problem, the LED's will likely be quite dim when the battery or charger goes to 13V, or even dimmer as the battery discharges to 12.4 or so.
And LED's for decent life over a variable input voltage range need to be driven by a constant current source to fix the brightness. Not any form of voltage source. LED junction voltage drops as temp rises, and if driven by a voltage source that results in a current increase, more junction voltage drop, more current..... then poof.
The best LED drivers actually use a pulsed current, LED's brightness is a non linear function of current, so higher current = much more brightness. so pulse the current and keep the RMS current to a good value= bright light, long life. Need to pulse the current fast enough not to cause visual flicker. but with the IC's available today not a problem.
all this doesn't come for free, that's why there are cheap LED lights and more expensive ones. You get what you pay for.
Actually you would be shocked just how little change in brightness a few tenths of a volt will cause with LEDs.. Most manufacturers are already running them at max current specs right out of the gate, dropping them a a volt isn't going to show up as a huge drop in brightness.
The "best" LED drivers do not intentionally "pulse" the LEDs, that is the old school method from back in the late 1970s.
Modern day LEDs are much more efficient and brighter that pulsing is no longer needed not to mention the digital outputs of things like clocks and displays was not filtered back and the LEDs pulsed to the switching speed of the drivers then causing the displays to appear flicker when a camera was pointed at it.
Now days the "best" method is to use a SWITCHING CONSTANT CURRENT REGULATOR. Switching regulators are far more efficient and the switching frequency is just above normal hearing range of humans. Care must be taken in the design and layout since they can and do generate RF noise due to the harmonics.. The output is DC and it is filtered well to reduce the harmonics.. So, no, you are not going to find a lot of those pulsing LED drivers unless it is a dirt cheap clock radio using LEDs..
