What wrong with direct drive?

badinstincts

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Many, or actually probably all these flashlights have a driver. But whats wrong with using direct drive if the battery voltage is perfectly within the limits of the led operating voltages?
Or even better, why not just use a capacitor only?

I dont care about having 3 different settings, high only is fine.

Dont many of these drivers create about 10-20% efficiency losses...
 
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127.0.0.1

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Many, or actually probably all these flashlights have a driver. But whats wrong with using direct drive if the battery voltage is perfectly within the limits of the led operating voltages?
Or even better, why not just use a capacitor only?

I dont care about having 3 different settings, high only is fine.

Dont many of these drivers create about 10-20% efficiency losses...

nothing is wrong with direct drive at all

BUT

with direct drive you now require an educated operator who can ensure the light is
switched off at the first sign of dimming, to prevent battery damage if the cells are unprotected

vendors don't want to build lights that can explode or break cells when misused,
hence the need for some smart circuitry which shuts off
the light before the battery goes too flat
 

TEEJ

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Exactly.

The lights start out bright as all get out, and get dimmer from that point forward as the cell loses power. The cell becomes the regulator...which, of course, means it can be over drained, etc.

The regulated lights that have constant out put might not be as bright at FIRST, because they are "pacing themselves" to run a steady race, as opposed to the unregulated light which runs every race as if it were a sprint...IE: It does the kick first, then runs slower, starts jogging, then jogs slower and slower until it has to walk, and then it collapses.

If that light is an ElektroLumens Big Bruiser for example, it burns like crazy for about 10 minutes, and by 20-25 minutes, the light is visibly dimmed, and if you left it on, bad things would happen.

A regulated light takes off at a steady jog that can go for sometimes an hour or more, so it never sprints, but it also never slows the jog either.
 

beach honda

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Direct drive is fine for small lights like my JiL J2 CR2. I use primary batteries only and it sucks the battery pretty dry. Will work in harsher environments like water since there is no driver to damage. The dimming lets me know I need to change battery. But for most all my edc lights, I prefer regulation,
 

Illum

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direct drive is actually preferred for an emergency light or one that I would take during an extended outdoor excursion. Without a driver, the reliability of the light increases and the runtime capability maximizes. This is due to the drop-out voltage of drivers as it struggles to maintain regulation. For a CC driver the headroom is usually 2V or so. If the battery falls below this range, and the driver cannot switch over to drive drive, then the light is as dead as a doorknob.
Direct drive ensures the emitter continued to put out light despite a depleting battery. Once the battery voltage falls below the LED's foward voltage internal resistance will turn the LED into a resistor, slowly limiting its foward current until the cell is out of juice. This is why fauxtons can still light up some 10-20 hours after it dims, although at that intensity it is hardly useful.
 

Th232

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Aside from the lack of output regulation, the natural variation in Vf from one LED to the next means that where one LED might put out, say, 200 lumens on a fresh battery while another might put out 170. From a manufacturer's viewpoint what should they put down as the output? Better to have a fixed number (and hence regulation) rather than say "tough luck" to someone who got the low end of the Vf lottery.

Also, for single AA lights, 1.5 V is going to do hardly anything to the LED.
 

qwertyydude

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One thing direct drive, or even resistor drive lights, have over regulated lights is their reliability in extreme situations. Unless your light's circuitry is specially potted and sealed, a light that becomes flooded with water will short out. A direct drive light or a resistor drive light will continue to function even if completely flooded with water.
 

M@elstrom

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One thing direct drive, or even resistor drive lights, have over regulated lights is their reliability in extreme situations. Unless your light's circuitry is specially potted and sealed, a light that becomes flooded with water will short out. A direct drive light or a resistor drive light will continue to function even if completely flooded with water.

Ah so that's rationale behind Dorcy's Metal Gear lights "unregulated" rugged dependability in a HAII shell with a polycarbonate lens & plastic battery caddy :D
 
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Chrontius

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One thing direct drive, or even resistor drive lights, have over regulated lights is their reliability in extreme situations. Unless your light's circuitry is specially potted and sealed, a light that becomes flooded with water will short out. A direct drive light or a resistor drive light will continue to function even if completely flooded with water.

I should point out that heavy potting is standard operating procedure around CPF for lights that aren't expected to be user-servicable (for values of service involving a soldering iron). Malkoffs do it, HDS does it, Nailbender will do it if you ask him to...

Elektrolumens does not. On the other hand, I can take my Blaster-NG down to individual components in ten minutes, and that's including the time it takes to warm up the soldering iron. If I ever get around to it, one of his 1990s vintage lights is getting an XM-L star.

There's no good reason for not potting a driver if you're not going to make a light that easy to mod. And some form factors, like the XR cans used early on by McGizmo, managed to be both potted and great mod hosts.

A second line of thought is that some driver circuits, like the Ra Twisty and the Joule Thief, can actually get more usable energy from a primary cell than a direct-drive light could, even one without the current-limiting resistor once your battery gets really dead.

PS: To answer your question, I hate having batteries that are producing usable light, but not enough. A good boost driver will keep them burning brightly until all the value has been sucked out. Throwing away half the energy in my primaries rankles, and I can't afford to switch everything over to guilt-free, as it would be a substantial (three digit?) up front investment. Also, primaries are way​ better for hurricane season down here.
 
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