Electronic – Best way to reduce battery consumption for LED device

battery-operatedled

I'm building a device that needs to "light up" to indicate status to the user. I of course want to use LEDs to light the device up, but I'm worried about battery consumption since I would like it to last for a year on batteries if possible. The device will be using its LED(s) for around one hour each day.

What are the best ways to get power consumption down for the LEDs? Using PWM? Is it better to use a high-intensity LED or several lower-intensity LEDs? Blinking the LEDs is ok, in fact that is the most obvious power-savings trick I've found.

Best Answer

Power the LED by a small flyback converter. The current limiting resistor can eat a lot of power. Note, this schematic is only an illustration. Some design/programming work have to be done.

Something like this:

schematic

simulate this circuit – Schematic created using CircuitLab

Here is a simple model (for LTSpice IV) of the above schematic. It demonstrated efficiency of 95% and higher:

Version 4
SHEET 1 880 680
WIRE 256 -160 -288 -160
WIRE 544 -160 256 -160
WIRE 256 -32 256 -160
WIRE 544 -16 544 -160
WIRE -288 96 -288 -160
WIRE 256 128 256 48
WIRE 544 128 544 48
WIRE 544 128 256 128
WIRE 256 176 256 128
WIRE 208 256 -48 256
WIRE -48 304 -48 256
WIRE -288 416 -288 176
WIRE 256 416 256 272
WIRE -48 432 -48 384
FLAG -288 416 0
FLAG 256 416 0
FLAG -48 432 0
SYMBOL nmos 208 176 R0
SYMATTR InstName M1
SYMATTR Value IRLML2803
SYMBOL ind 240 -48 R0
SYMATTR InstName L1
SYMATTR Value 100µ
SYMATTR SpiceLine Rser=1
SYMBOL LED 560 48 R180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 2
SYMATTR InstName D1
SYMATTR Value NSSW008CT-P1
SYMBOL voltage -288 80 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value 5V
SYMBOL voltage -48 288 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V2
SYMATTR Value PULSE(0 4 0 10n 10n 3u 50u)
TEXT -322 456 Left 2 !.tran 1m
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