DB400 Questions

[Illuminated]

I'd like to drive a low Vf Luxeon (Q2H) from 3AA alkalines using a DB400. I may have missed it, but I don't think I've seen it done.

1) Is it feasible?

2) Run time?

3) Does it have a reverse polarity protection diode on the input that can be bypassed to stay in regulation down to a slightly lower Vin? (At the risk of having no polarity protection, of course...)

Thanks in advance - John

 

[dat2zip]

The DB will maintain regulation downto the Vf of the LED. Below that, it drops into DD which is nice, since you won't see the transition.

Not sure about 3, but as I explained above, at Vf and below, it's in DD mode.

Not sure about run time. A rough estimate is to compute amp /hrs or watt/hrs.

Assume 80% efficiency on the converter. That would mean the input would draw 0.4A / 0.8 = 0.5A. With 1800mA/HR NiMH for example you could approximate that to be 18000 / 500 or approximately 3 hours of run time.

This is a very crude and rough approximation. It will probably be less than that. You can look up the capacity rating for Alkaline batteries or others to see what the approx difference in runtimes would be.

Wayne

 

[Illuminated]

Thanks Wayne - I might go ahead and prototype this setup just to see what happens.

I'm thinking that some reasonable period of regulated run time, followed by a declining output might be desirable versus over-driving (DD) the heck outta the LS, followed by a similar decline in output...

Thanks again - John