Help translating and/or sourceing electrical components for the LED headlight project

[3Phase]

... this circuit would need about 16 - 18 volt source to supply constant current at 12 volts ...

Terry, I think he's using ~4 volts, not 12, but that LED driver chip looks cool for a headlight circuit.

I've used 555s, 741s or just a couple of 3904s to make astable multivibrators (oscillators) to drive LEDs. If you drive the LEDs at a medium frequency, one that's not visible to the naked eye, instead supplying a constant current and voltage that will reduce the duty cycle. With a reduced duty cycle you have slightly less heat with the same apparent output and/or you can raise the voltage a bit to get a brighter-looking output without blowing up the LEDs.

This is a fun little project you've got here!


Regards,

Scott

[b.walker5]

Hmmm, Multi-vibrators in a stable .... Sounds like something my horse mad wife would be interested in..

Seriously though, I know what your talking about, and if using an oscillator to drive leds at a fixed frequency works okay then how hard would it be to produce the variable output required for the daylight pulsing effect ?

[81xsproject]

Okay, so maybe you all can help me some more, as I can't get the author of the Instructable to answer my question. You may have noticed that there are some discrepancies between the parts shown in the schematic and those listed in the BOM. For instance, the schematic shows C1 and C3 as 4.7uF but the BOM lists them as 10uF and 1uF. The second discrepancy is in the 12v to 5v circuit on the right side of the schematic; D5 is listed as ONE OF THESE ZENER DIODES and the BOM lists THIS. Any ideas...?

[3Phase]

Okay, so maybe you all can help me some more, as I can't get the author of the Instructable to answer my question. You may have noticed that there are some discrepancies between the parts shown in the schematic and those listed in the BOM. For instance, the schematic shows C1 and C3 as 4.7uF but the BOM lists them as 10uF and 1uF. The second discrepancy is in the 12v to 5v circuit on the right side of the schematic; D5 is listed as ONE OF THESE ZENER DIODES and the BOM lists THIS. Any ideas...?

C1 and C3 are being used as electrical current shock absorbers. Within reason, if you need to absorb a bigger current spike, use a bigger capacitor. If it's used in a 'clean' environment -- not your motorcycle! -- then use the smaller capacitors. I'd stick with the 10uF and the 4.7uF.

The circuit with D5 is showing a 3 terminal surface mount zener diode package. Only pins 1 and 2 are available, as shown in the schematic, because the 3rd terminal of the MMBZ5231BW-FDICT-ND is just a dummy so the 3-terminal chip laying machines don't choke and the employees don't get confused.

I don't know why the BOM lists D5 as a ZXLD1360. Have you read the 1360 spec sheet?

That's not a IC voltage supply for a LM555 it's a 1Amp LED driver; a fancy one-chip solution for the assortment of multivibrators I mentioned above. It can be driven up to a frequency of 1MHz with a 95% efficiency. I guess the boys on the white coats have been busy.


Regards,

Scott

[Just In Case]

About dimming. You see that PWM input to the chip? If it is fed a high, there will be current output, a low will switch off the output. So you can pulse it with a binary signal.

I'm thinking you are have 4 strings of three LEDs? Two strings for low beam, and all four for high beam? To get tricky, you can have one low string on continuously and just pulse the other to give a flicker effect. Or pulse them alternately - string 1 on/string 2 off then string 1 off/string 2 on.

Hella does tail/brake lights with ~six rows of ~eight LEDs. Their research has it that they are more effective when the tail lights compose of using the center four rows and center 6 columns lit dimly, the when the brake lights are required, light all the row/columns at full brightness.

From this I suggest you have an inner ring of three and an outer ring of three. Flash each ring on and off alternatively, but have both rings on before switching the other off. A Picaxe 08 controller is cheap enough to do the switching, but you need the programing board which will hurt the costings for a one off project. Someone smart enough could do it with discrete components.

Another way to flicker the light output is to dicker with the feedback resistance as the system runs. But we are talking about such a low resistance value, I'm not sure how to do it safely. Perhaps two resistors in series (both 0.11?) and have a mosfet across one to take it out of the feedback circuit by shorting it out. Some experimenting will be required to settle on the resistor values. The values are so low that that lead resistance could come in play if you need to mount the mosfet out of the way. At least with this way the current can be varied analogue and not hard on/off like PWM does if you don't switch the mosfet on/off and instead vary its gate voltage. You can use transistors, it's just when they're hard on there is typically 0.6V lost across the CE junction so a bit more fiddly to determine the resistor for 900mA. Off course you still need to develop a circuit to do the flickering, but you need to do this regardless of your implementation.

[tw1980]

Terry, I think he's using ~4 volts, not 12, but that LED driver chip looks cool for a headlight circuit.

I've used 555s, 741s or just a couple of 3904s to make astable multivibrators (oscillators) to drive LEDs. If you drive the LEDs at a medium frequency, one that's not visible to the naked eye, instead supplying a constant current and voltage that will reduce the duty cycle. With a reduced duty cycle you have slightly less heat with the same apparent output and/or you can raise the voltage a bit to get a brighter-looking output without blowing up the LEDs.

This is a fun little project you've got here!


Regards,

Scott

Hmmm,

Interesting idea.I guess finishing off that bottle of tequila that night didn't destroy your brain cells.LOL I was thinking LPF but if the LEDS can be pulsed and the duty cycle controlled this could work.A square pulse would switch the junction on the LEDs on and off quicker dissipating less heat right?I think this is a good idea and I'm starting to rethink my pessimistic view. If I get some time this weak I might look up some specs. Terry

[3Phase]

Hmmm,

Interesting idea.I guess finishing off that bottle of tequila that night didn't destroy your brain cells.LOL

Oh, the tequila was just fine! but the nice rangers with the shiny new nightsticks were thinking about it. Just when I had my liberal friend boxed into a logical corner with my flawless, vociferous arguments the local gendarmes showed up and saved his metaphorical bacon!

I was thinking LPF but if the LEDS can be pulsed and the duty cycle controlled this could work.A square pulse would switch the junction on the LEDs on and off quicker dissipating less heat right?

Absolutely.

I think this is a good idea and I'm starting to rethink my pessimistic view. If I get some time this weak I might look up some specs. Terry

It the same idea as the scanning electron beam in a television picture tube: just enough to light up the phosphors and fool the human eye but not long or strong enough to burn the phosphors and ruin the tube, or the viewer.


Regards,

Scott

[81xsproject]

My current kitchen remodel has EVERYTHING else back-burnered at the moment. So, I don't have much progress to report. In the down time I am working on sourcing the heat sinks I will use as part of the housing. My buddy works on radios for Raytheon so I have him keeping an eye out for finned heat sinks large enough to cut a 6" diameter circle from. If anyone else has any ideas or leads for this, please let me know.
I also have another electroni-XS project on the board that EVERYONE will want...TOP SECRET!

[Just In Case]

...I also have another electroni-XS project on the board that EVERYONE will want...TOP SECRET!

You're no fun. Spill the beans

[81xsproject]

Sorry, it's still in the dream phase. However, if feasible, it is just too awesome.

[81xsproject]

Well, screw this idea. I was all about doing this particular board all DIY, pcb, components, soldering, etc. Then this morning I happened to stumble onto a VERY important detail that I previously overlooked. The IC is 3mm ON ITS LONGEST SIDE! Danm! I am adventurous, but know my limitations. Looks like I'll be building this instead. Much simpler, not as efficient.

[81xsproject]

Well, I finally order the parts for the deadlight and 'other' project today from digikey today. Soon, i shall post some pics of me testing lights.

[psycoreefer]

I was really interested in this little project, any updates?

[81xsproject]

Well, I tested out the power supply circuit and it works great. It is insane how bright just one of these leds is. Just doing some quick on an off again testing (because no heatsink yet), I saw little white spots for about a half hour. i also tried putting on the lens/reflector and it really takes the beam down to a nice 10-15 degree pattern. These LEDs are a little blue-er than I would like, but still quite white. At this point, the hold up (other than my kitchen remodel) is that I have yet to find something I could salvage heat sink material from. I want it to be finned for max cooling, but I need something I can cut at least a 5" diameter circle from. I plan to run the LEDs at their upper limits (becuase I really am XSive like that ) so they have to stay cool or it will shorten thier life span. I have been considering going down to the hardware store, buying the metal cutting skilsaw blade, and installing it on my table saw. I could then cut the fins myself into some Al block. If anyone has any ideas for a possible finned heatsink (Al, Cu, brass) source, please let me know. It doesn't need to be super heavy duty, but the opposite side needs to be a nice flat surface.

[psycoreefer]

have you considered using some computer heat sinks? Like off of the CPU's or GPU's. I know you'd have to use several to get a 5" area covered but you could probably pick them up for little to nothing if you've got a small time computer "repair" shop around, they've likely got tons of "junk" computers you can rob.