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The stars...

  • ndwalters Sunday, November 13, 2011 7:44 PM Reply
    Posts(8) | Reviews | Tip post

  • MedvedBrundibar Sunday, March 25, 2012 1:20 AM Reply
    The PWM on 7135 does not work via dedicated PWM input, but via it's supply pin (7135 supplied => LEWD ON, no supply => LED OFF). This could be easilly handled by the microcontroller, as the supply current is only 200uA per regulator chip.
    The drawback is, then the regulator have to always "cold start" (all internal blocks have to start up, include the reference generator, what is usually rather slow), what take some time (I would guess some 100 us), so the PWM signal should be slow (~100..150Hz - so it does not flicker yet, but still the turn ON delay is of no problem).

    Regulators with dedicated PWM input keep the slowest blocks (the reference,...) permanently ON and only gate the output stage, what then yield responses in low us range, so kHz PWM is OK.

    When modding this circuit (with new firmware) I would implement the "MID" (33%) setting by turning ON only one of the three regulators (so one 7135 would be supplied from the PWM channel, other two from another output pin) and only lower setting would use the PWM. At first the LED would work in lower current, so more efficient mode, but mainly for lower setting the PWM duty would not be as low (e.g. "3%" would need 10% duty, what is way easily handled by the regulator than the direct 3% duty when all sources are controlled by the PWM)

    But I guess that would be one of the dream projects - as I know myself, when something work (and the stars seem to do the job), I won't find time for that anymore...
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  • sheepish Top 10 Forum Poster Sunday, March 25, 2012 4:29 AM Reply
    the PWM signal should be slow (~100..150Hz - so it does not flicker yet, but still the turn ON delay is of no problem).

    And yet... the AMC7135 works fine at 4.7 kHz. It's a great regulator, and worth learning more about before explaining in great detail why it can't work as it does.
    Remembering 30 years.
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  • DrJones Tuesday, April 24, 2012 3:56 PM Reply
    The AMC7135 takes about 2us to start.
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  • graneyc Wednesday, December 12, 2012 11:50 AM Reply
    "The 4 stars are connections for a twist head on a flashlight"

    I really hope you are correct!

    I just placed an order for one of these. I'm going to attempt to rebuild a Vetta NiteVision 3L. {REMOVED} has these headsets for pretty cheap (probably because the lights are crap). It has a twisty head w/ 4 positions that connect to it's current board in a very similar fashion to what we see on this board. It's going to be tricky to get everything to line up the same, but I'm pretty sure I can make that part of it work. I plan to post a how-to if I can get this to work; I'll be sure and drop a link to it on this thread when I do.

    If all that doesn't work, I suppose I'll have to figure out how to wire up a clicky switch. Either way, after adjusting these light to crank out this must juice at full blast, I expect my head to shine w/ the brightness of a small sun. I'm sure I'll end up running them at medium or low most of the time.
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    mod edited by cyclist on 12/19/2012 at 6:44 AM
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