I might be a bit hesitant to carry that on the street - if a cop saw you with that in your hand, he might be inclined to shoot first and ask questions later! :gun:
Anyway, I have been researching drivers lately, and I had some serious questions about that chip you are using.
'Um, did anybody take a CLOSE look at that data sheet?
The stuff at the top kinda reads like someone's recent description of 4x's as the "ultimate" diode that everybody wants!
But when you get down into the fine print, and look at the detailed specs...
According to the specs, specified load regulation is only guaranteed for output currents of under 250ma?
Operating above 200ma requires use of a larger, more expensive support component.
Max output current and conversion efficiency in "boost" mode also appears to vary quite a bit, based on operating conditions. In a different example on their web site, max output was 250ma. In many cases, efficiency drops like a rock after 100ma. And in all of the efficiency graphs that show the "less noisy" mode (the other mode generates a huge amount of switching noise and voltage swings that increase with current and would IMHO pbly not be safe for a laser diode), all of the lines "die" at about 250ma.
Unlike the spec sheet for something like the LM1117 (used by rkcstr, I believe), which discusses things like the amount of copper area on the circuit board for cooling, and heat sink size vs. maximum current, this data sheet has nothing about any of that. But that becomes clear when you look at the package info and realize, this chip doesn't appear to have any kind of heat sinking on it!:undecided:
This appears to be a low-power device, designed primarily for converting battery power to the correct voltage to operate digital circuitry (such as 3.3V or 5V) like used in digital cameras.
Max output voltage according to the specs is also 5.5V, NOT 5.6.
So no way is this going to be good for 8x! Probably not enough to fully push a LTC either.
But I saved the best (or worst!) part for last!
(The following assumes the statement made by the seller above in post #7 is accurate)
The last schematic on the data sheet (Figure 3, pg. 9) is for the low-noise version of an adjustable VOLTAGE regulator. :huh:
NOT a current regulator. A frk'n voltage regulator! :wtf:
(Given the design of this device (especially how the low noise mode is implemented), I don't know if it is even capable of being used as a current regulator. The data sheet does not indicate that it can)
A current regulator is the whole reason you normally buy a driver for - it's what keeps your laser diode from going into thermal runaway and self-destructing!
So, other than boosting the voltage enough to fire-up the laser, what you've basically got is a Kipkay laser!
Actually, maybe even worse! Follow me here...
When a laser diode starts to get warmer (say you've been holding down the button trying to line-up the beam with that damn match!), its resistance starts to drop. When that happens, it starts to draw more current.
(It's at this point that a driver normally saves your ass, by "backing-off" to keep the current in check, and preventing your diode from drawing more & more power and going into thermal runaway)
When resistance drops, if the current is held constant, the voltage drop across the diode goes down as well. (V=IR)
But a VOLTAGE regulator is going to see that and say -
"Hey, the voltage is going to drop below what it is suppose to be! I have to pump MORE current into the circuit, to keep the voltage level!"
Yep, that's right, when a voltage regulator sees your laser diode overheating, it feeds it MORE power!
This causes your overheated diode to get even HOTTER, which lowers its resistance even MORE, which causes the driver to feed it even MORE current to maintain the same voltage...
You can see where this is going. The laser and the voltage regulator are in a feedback loop, each accelerating the thermal runaway.
Think Star Trek "phasor set on overload", and you get the general idea!
That's probably why the warning about turning the volume up. With a voltage regulator, you can't run the diode at full power without risking destroying it due to thermal runaway.
Well, I guess now we know at least why they're shaped like hand grenades!:crackup:
Also explains the lower power setting on that one. As well as the odd use of an externally accessible pot. A standard current regulator you could just set it (connected to a dummy load) and forget - it will now work with any PHR. But a voltage regulator, you would likely have to adjust it for that specific diode. And if/when you burned it out, have to re-tune it for the new diode (due to differences in diode efficiency causing different current draws for the same voltage), even if they were the same model diode. You would also have to adjust it with the laser running. An easy-access pot would be useful (if not required) in that case.
Hmm, perhaps buyer beware, methinks? :undecided:
LOL
