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Thread: Brinkmann LED Flashlight Explained, + Circuit diagram

  1. #1
    Flashaholic* MrAl's Avatar
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    Default Brinkmann LED Flashlight Explained, + Circuit diagram

    Hello all,
    I got interested in the LED flashlight too
    and decided to do a little investigation.
    I took it apart as per instructions i found
    on this site (thanks to all who posted)
    although i had to keep pressure on the
    barrel in order to keep the plastic
    tabs from popping back in while i tweeked
    the other 3 tabs.
    Anyway, i did a fairly
    complete analysis and posted the circuit
    diagram complete with parts list and waveforms
    on my home page and at another site.
    Here is the explanation site: http://forum.howstuffworks.com/showt...c&Number=46128
    and here is my home page (which you can also
    reach from that url too) http://members.aol.com/Xaxo/
    with the full schematic/parts list/waveforms.

    Enjoy, and feed back, results etc would
    be appreciated.

    --Al

  2. #2

    Default Re: Brinkmann LED Flashlight Explained, + Circuit diagram

    What a great drawing!
    I see why my attempt did not work.
    Good job!

  3. #3
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    Default Re: Brinkmann LED Flashlight Explained, + Circuit diagram

    Wow!! I'm still trying to draw out the diagram, but you have not only drawn it out, but also a schematic and a full explaination.

    Thanks! [img]images/icons/smile.gif[/img]
    I'm still trying to digest it though [img]images/icons/tongue.gif[/img]

  4. #4
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    Default Re: Brinkmann LED Flashlight Explained, + Circuit diagram

    <BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
    Anyway, i did a fairly
    complete analysis and posted the circuit
    diagram complete with parts list and waveform
    <HR></BLOCKQUOTE>

    Very well done Al!
    I have a few remarks:
    <BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>
    While L dumps its current through the LED, the voltage across the LED falls only slightly because of the nonlinearity of the LED
    <HR></BLOCKQUOTE>

    If you look only at the interesting part of the LED's U/I diagram (lets say in between +20mA and +80mA) it is pretty linear. It is just no resistive load. You could look at it like a 3V voltage 'sink' with a 25 Ohm resistor in parallel (values estimated). Linearity does mean that (in the part we look at) the U/I diagram makes an even line, but not necessarly that this line hits the 0/0 point. If you learnt another definition of 'linearity' at school (in it's electrotechnical meaning) please let me know.

    <BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>
    In other words, if you were to supply about 40ma continuous uninterrupted
    current flow through the LED you would get the same level of light output from the LED
    as you do when pulsing it at a higher current which averages 40ma
    <HR></BLOCKQUOTE>

    First you do not state which kind of average you are referring to )or have I overlooked it?). Is it arithmetic average or RMS or whatever?

    And then, the LED's light output over current is not linear. At higher currents the efficiency is lower. So pulsing a white LED with a perfect square wave and a 50% duty cycle will NOT give the same light as half the current. (besides, as you did not state that: Also the LEDs power consumption is higher in pulsed mode)

    Don't get me wrong: I'm very happy that you did this more than exemplary work. I would not have made it almost as nice and will probably have many other errors in it.

  5. #5
    Flashaholic* MrAl's Avatar
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    Default Re: Brinkmann LED Flashlight Explained, + Circuit diagram

    I got interested in the flashlight and then i found all the info on
    this site about different flashlights and tests and all, so i thought i
    would contribute to the information pool also by determining how the
    flashlight circuit was made and how it worked so that others could
    build their own home made flashlights and power them up with circuits
    similar to this one and install them in whatever flashlight they wanted
    to. Having posted the schematic and brief explanation, i feel i have
    acheived that goal.

    Some of the points you made were interesting, and i would like to
    explain a few things pertaining to those remarks.

    First, the definition of 'linear' is:
    the multiplication of the voltage by a constant k results
    in the multiplication of the current by the same constant k.
    The LED is certainly not linear, and doing a nonlinear analysis
    anyway, i saw no need to use a piecewise linear approximation.
    If you still are not comfortable with calling the LED v/i curve
    nonlinear, then simply substitute the words
    "v/i curve of the LED"
    for the words
    "nonlinearity of the LED"
    and re-read the sentence.

    Secondly,
    when i say "average" i mean "average". Whenever someone says average, they
    mean the arithmetic average and not the geometric average, harmonic average,
    square root of the mean of the square, ninth root of the velocity of
    the speed of light in a vacuum times the current cubed, or anything else :-)

    Third,
    when i said the pulsed current produces the same light as about
    the same average current through the LED would produce, i meant just that too.
    The reason for this is quite simple: when you half the time of the light output
    you half the total amount of light being output, and when you double the current
    to the LED you approximately double the light output from the LED. When you do
    both, you get the same output as if you supplied about the same continuous current
    to the LED as the average of the pulsed current. Yes the led is more inefficient
    at higher currents, but it will be hard to notice a difference. Also, 'about'
    means just that too.
    For most practical purposes, when you supply 'about' the same constant current
    to the LED as an averaged pulsed current, you get 'about' the same light output.

    Lastly, i will post updates when i do more with this circuit.
    I did find already that the circuit can operate on a single
    AA battery with slight mod's. I built up a similar circuit
    using the parts list shown (with the schematic) and wound
    a toroidal coil measuring about 220uH. I got about the same
    results as the original circuit. The thing i really like
    about this circuit is that the parts are so dirt cheap. Its
    much cheaper then buying evaluation boards for parts that will
    cost $4.00 just for the ic. Im thinking of using a MOSFET
    output transistor to increase efficiency. Only problem is,
    that will raise the price tag a little. With the transistors
    in the parts list, this circuit can be built for under
    75 cents.

    As i do more tests ill post the results here so everyone can
    build the circuit and modify it to fit any number of LEDs
    and battery cells they wish to use with their flashlights.
    I would hope that anyone else working with this circuit would
    post their results as well.

    Good luck with it,
    --Al

    PS. Special thanks to Stingmon for the use of the WCT graphic.

  6. #6

    Default Re: Brinkmann LED Flashlight Explained, + Circuit diagram

    <BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
    when i say "average" i mean "average". Whenever someone says average, they mean the arithmetic average and not the geometric average, harmonic average, square root of the mean of the square, ninth root of the velocity of the speed of light in a vacuum times the current cubed, or anything else :-)<HR></BLOCKQUOTE>

    LOL!! This is my kind of humor.. [img]images/icons/smile.gif[/img] [img]images/icons/smile.gif[/img]

  7. #7

    Default Re: Brinkmann LED Flashlight Explained, + Circuit diagram

    Great work MrAl!

    The Brinkman circuit is nearly identical to the "solar powered LED walkway light" mentioned in this thread:
    Want a LED flashlight with only 1 AA?

    The circuit (minus a few parts which are the photocell switch) is shown here.

    The parts have slightly different values and the solar light circuit has one more resistor and capacitor from the battery + side to the base of the PNP.

    Thanks for the explanation of how the circuit works. It sounds as if you ran it through a PSpice circuit simulator.

    One thing about all these types of circuits is the large peak current through the LED. This peak is usually much higher than the LED manufacturer's "absolute maximum rating" for the LED current. I've exceeded these maximum ratings before with bad results, i.e. destroyed parts, so I have great respect for them.

    One modification to the circuit which would smooth out the current pulses in the LED and lower the peak LED current would be to add a Schottky diode between the Q2 colector and the LED anode. Then add a 10uF (2.2uF might work just as well), low ESR, tantalum capacitor from the junction of the cathode of the new Schottky/LED anode, and ground (emmiter of Q2). This would stabilize the current pulses in the LED.

    Unfortunately it would also decrease the overall effiency of the circuit because of the drop across the diode, leading to slightly shorter battery life.

    You might be able to get this effeciency back by using a Zetex ZXT14N20DX transistor in place of Q2. This part has a saturation voltage of ony 30mV at a colector current of 1A! Wow! A bit costly though. Also using an inductor with a very low DC resistance would also help.

  8. #8

    Default Re: Brinkmann LED Flashlight Explained, + Circuit diagram

    Thanks. I really appreciate everyone's willingness to share.

    I'm most interested in a light circuit with three or four leds and maybe two batteries. I've looked at the Brinkman light in the store a couple of times, but one led doesn't seem like enough for a package of that size and weight.

    What would it take to make it work for multiple leds?

  9. #9
    Flashaholic* MrAl's Avatar
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    Default Re: Brinkmann LED Flashlight Explained, + Circuit diagram

    Yes thanks for all the inputs in the various threads; it is very interesting to hear about other's experiences with these things.

    <BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by jeff1500:

    What would it take to make it work for multiple leds?
    <HR></BLOCKQUOTE>

    I'm going to try that soon too :-)
    Right now i think you can just connect two
    in series. Just how many you can connect
    in series is probably dependent on the design
    of the coil (Brinkmann). The coil will have
    to sustain a higher voltage while pumping the
    LED's. If its made well enough it could handle several in series.
    My guess is that a better coil with lower inductance will handle more LED's in series,
    and lower series R will handle a few in parallel too.
    I guess it will have to be tried to find out :-)
    As usual, ill post any results i get here in one of the threads.

    Good luck with your LED circuits,
    --Al

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