This request relates to creating a torch/flashlight with a very low light output mode - one that has sufficient illumination to be useful over a few feet in total darkness, whilst being "always on". So I am looking at tens of microAmps (9v) battery powered on a small pcb footprint - fixed rate pwm seems the most efficient way to go. Testing so far indicates that I need to drive a LED at a PWM duty rate of < 0.4%.
Thus far I have tried a 555 running at 160kHz driving a 14 bit counter. Using a couple of D-type latches I let one clock pulse through when the counter upper bit ticks over. That way the pwm ratio is clockwidth/totalpulses. But that is 3 ic's plus ancillary passive parts and a significant clock rate, ending up at a low refresh rate at the led. What I would prefer is just the one ic and a clock/update refresh ~ 50Hz.
Thus far I have tried a 555 running at 160kHz driving a 14 bit counter. Using a couple of D-type latches I let one clock pulse through when the counter upper bit ticks over. That way the pwm ratio is clockwidth/totalpulses. But that is 3 ic's plus ancillary passive parts and a significant clock rate, ending up at a low refresh rate at the led. What I would prefer is just the one ic and a clock/update refresh ~ 50Hz.
I haven’t tried yet but I read that a 555 won't get down to this sort of pwm ratio.
There is a LTC6992 pwm generator, but that is 5v only.
There are generators designed for PSU control (also not tried yet) but these tend not to cover the full 0-100% duty range - or so I read.
Would appreciate experienced views on what might be my best approach so I might be able to avoid at least some blind avenues.There is a LTC6992 pwm generator, but that is 5v only.
There are generators designed for PSU control (also not tried yet) but these tend not to cover the full 0-100% duty range - or so I read.