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Low Power Usage?

Xer0

Xer0

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Im always reading here about the Laser' behaviour at the Threshold current. that it can jump from LED to dangerous in just smallest turns of the pot. and even badder, with rising temperature it drifts.

Is there actually a chance to make this Diode stable at low powers?
I want a reasonable pointer, expecting 5-15mW. 50mW would be the absolute max i take!

Idea: setting it at 100mW and putting an OD2 in front, so -> 10mW. Will the filter sustand the 90mW it must dissipate for longer time?
 





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dnar

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Just buy the cheapest Chinese 100mW pointer you can find. Less than 50mW for certain.
 
Xer0

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Im not talking about 405nm or Green, im talking about 445nm...
 
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dnar

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Sorry, my mistake. I just have taken a cue from th\e sub-forum name!
 
Prototype

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You could mount a glass ND filter in front of the final lens. At <50mW or so the 445nm diodes have been found to be single mode, although I'm not sure how stable this would be in a pen host due to heat.
 
Xer0

Xer0

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ND is "Natural Density" Glass? where can i get small peaces cheap? found only 5cm² , 100$
 
RA_pierce

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I haven't plotted any of my own diodes, but from what I read, threshold is around 200mA. As temperature rises, the Ith may drift higher, resulting in lower output.

Also, I read that at threshold, the diode will begin to lase at 20-30mW. If the laser is set to 50-60mW, it should be well enough over threshold to avoid instability.
Instead of buying a new ND filter, why not just take some coated optics from a DVD burner or PHR sled you have laying around?
If you use the right piece of glass, you can cut the power to half or less.
Also, if you use an Aixiz acrylic, you may not even need to use additional optics to drop the power.

Powering the diode at ~250mA should get you 50mW more or less after a collimating lens. Since the diode needs about 4V, the total power input would be 1W. With 50mW out, you will need to dissipate ~950mW of heat.

A laser set at this power could work pretty well in a pen host with a decent duty cycle.
 
Xer0

Xer0

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Would PWM be an option? done in SMD, it could maybe fit in a 2xAAA host with an 10440...

Yes have some PHR, one GGW, LPC and a bunch of KES Sleds here. what could i use?
 
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Canuke

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BShanahan14rulz said:
instantaneous power will still be 100mW
Click to expand...

That's a function of the PWM frequency. Obviously, a 1W peak PWM 445nm laser with a 10% duty cycle but a 1 Hz frequency is still delivering a 100ms pulse of 1W power, which is plenty dangerous. At a sufficiently high frequency such that each individual pulse does not exceed that total energy threshold, this laser becomes functionally equivalent to a 100mW continuous output.

I've been wondering why there's not much discussion around here (that I've seen, anyway) of using PWM drivers with adjustable duty cycle to vary laser outputs.... is this "instantaneous power" thing the reason why? There are plenty of LED drivers that do PWM in the kHz range...
 
BShanahan14rulz

BShanahan14rulz

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Canuke said:
At a sufficiently high frequency such that each individual pulse does not exceed that total energy threshold, this laser becomes functionally equivalent to a 100mW continuous output.

[some other stuff]

There are plenty of LED drivers that do PWM in the kHz range...
Click to expand...

This I can agree with. As frequency increases, it becomes functionally more like a 100mW laser. But with lower frequency PWMs, I don't want to assume that the gel in my eye can spread that heat fast enough to keep the energy density down in the one spot that the 1W pulse just hit.

Thing is, common LED "drivers" that do PWM seem to do it in the Hz range. You'd be paying more for one of the nicer ones that PWMs at a higher frequency, for some reason. I don't really understand why they use low frequency PWMs, must be cheaper, but they look awful.
 
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Canuke

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BShanahan14rulz said:
Thing is, common LED "drivers" that do PWM seem to do it in the Hz range. You'd be paying more for one of the nicer ones that PWMs at a higher frequency, for some reason. I don't really understand why they use low frequency PWMs, must be cheaper, but they look awful.
Click to expand...

I've wondered about that, whether frequency in power drivers is hard to get over 100 Hz without putting out for pricier components and/or more complex designs. But I've not done flashlight builds, and so am less familiar with LED-oriented drivers and the obstacles to building high-frequency drivers. I do know that the frequency of the PWM driver in my 4Sevens Quark Mini is well into the KHz range.

It sounds like a good question for drlava and the other driver guys.
 
BShanahan14rulz

BShanahan14rulz

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4sevens makes much better lights than those that I own. I'm not surprised that they didn't skimp on the PWM frequency :beer:
 
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