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"Glowtorch-type" mod (200mw 660nm red)

chimo

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I forgot to mention that increasing the drive current to around 258mA made a noticable increase in output. It definitely burns faster and is likely closer to spec.

When the "non-broken" ones start rolling out I would be curious of the current draw from the batteries. The draw from the batteries will be almost the same as what the LD sees. This laser could likely be used with 1x RCR123 and a blank feed-through spacer. It may require a change in the 4.7 ohm resistor on the positive battery wire.

Paul
 



Bernhard

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Wow! Thank you very much for your diagram and analysis, Paul.
Any idea what resistor need to be changed to other value to increase the drive current past 258mA?
I would love to get minimum drive current starting around 200mA at minimum pot and beyond that on max pot...
 

chimo

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Bernhard said:
Wow! Thank you very much for your diagram and analysis, Paul.
Any idea what resistor need to be changed to other value to increase the drive current past 258mA?
I would love to get minimum drive current starting around 200mA at minimum pot and beyond that on max pot...

I did not go all the way up with the pot.  It should go well above 258mA - I stopped there because I did not want to overdrive the poor LD too much. If you want to go really high, say 800mA, you will have to remove/reduce the 4.7ohm resistor - it will drop too much voltage for the circuit to stay in regulation.  

The other things that must be considered is if the op amp will provide enough base current to drive the transistor and that the transistor is not over-driven.  
The transistor limits:
Icmax = 500mA
Vcesat=0.5V
Max power dissipation 1000mW
hfe is around 30.

Base drive will be <20mA.  The op amp should be able to drive that level.

NOTE: THIS IS A SIMPLIFIED EXAMPLE. SOME FIGURES ARE ESTIMATED, SOME CIRCUIT LOSSES ARE IGNORED AND SOME CIRCUIT DYNAMICS ARE IGNORED.

EXAMPLE 1: (258mA drive, 2x CR123)
Assumptions: Batt voltage = 5.8V(estimated sag under 250mA load), LD voltage = 3V @ 258mA.

4.7 ohm resistor (0.258 x 4.7 = 1.21V.   Power dissipated = 323mW)
LD (approx 2.5V to 3.xV - depends on operating curve - let's assume 3V. Power dissipated = 774mW)
1.5 ohm resistor (0.258 x 1.5 = 0.387V.   Power dissipated = 100mW)
Transistor (Battery voltage minus all the other drops. 5.8V - 1.21V - 3V - 0.387V = 1.2V.  Power dissipated = 310mW)

Looking at this example, total power from the battery is approx 1496mW.  Power to the LD is 774mW.  Efficiency = 52%.



EXAMPLE 2: (500mA drive, 2xCR123)
Assumptions: Batt voltage = 5.6V(realistic sag under a 0.5A load), LD voltage = 3.3V @ 500mA.

4.7 ohm resistor (0.5 x 4.7 = 2.35V. Power dissipated = 1175mW)
LD (3.2V Power dissipated = 1600mW)
1.5 ohm resistor (0.5 x 1.5 = 0.75V.   Power dissipated = 375mW)
Transistor (Battery voltage minus all the other drops. 5.6V - 2.35V - 3.2V - 0.75V = -0.7V!! Circuit will not stay in regulation!)
Since Vcesat=0.5V, the 4.7ohm resistor has dropped at least 1.2V (0.5+0.7) too much. Resistor would have to be reduced to 3ohms or less or removed.  You would have to do these caluclations for the upper and lower of your supply voltages.



EXAMPLE 3: (500mA drive, 2xCR123, remove 4.7ohm resistor)
Assumptions: Batt voltage = 5.6V(realistic sag under a 0.5A load), LD voltage = 3.3V @ 500mA. **Remove 4.7ohm resistor.**

LD (3.2V Power dissipated = 1600mW)
1.5 ohm resistor (0.5 x 1.5 = 0.75V.   Power dissipated = 375mW)
Transistor (Battery voltage minus all the other drops. 5.6V - 3.2V - 0.75V = 1.65V.  Power dissipated = 825mW)
Efficiency = 1600/2800 = 57%

This circuit would stay in regulation until the battery voltage drops another 1.15V because Vcesat of the transistor is 0.5V.
Efficiency (@Vbatt = 4.5V) = 1600/2250 = 71%


HTH,


Paul


EDIT: battery voltages adjusted to indicate realistic sag under load.
 

chimo

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EXAMPLE 4: (258mA drive, 1xR-CR123 Li-ion, remove 4.7 ohm resistor)
Assumptions: Batt voltage = 3.85V, LD voltage = 3V @ 258mA. **Remove 4.7ohm resistor.**

LD (approx 2.5V to 3.xV - depends on operating curve - let's assume 3V. Power dissipated = 774mW)
1.5 ohm resistor (0.258 x 1.5 = 0.387V.   Power dissipated = 100mW)
Transistor (Battery voltage minus all the other drops. 3.85V - 3V - 0.387V = 0.463V. Higher than Vcesat!!! Power dissipated = 120mW)



EXAMPLE 5: (258mA drive, 1xRCR123 Li-ion, remove 4.7ohm resistor, smaller sense resistor)
Assumptions: Batt voltage = 3.85V, LD voltage = 3V @ 258mA. **Remove 4.7ohm resistor & Replace sense resistor w/ 0R5.**

LD (approx 2.5V to 3.xV - depends on operating curve - let's assume 3V. Power dissipated = 774mW)
0.5 ohm resistor (0.258 x 0.5 = 0.129V.   Power dissipated = 33mW)
Transistor (Battery voltage minus all the other drops. 3.85V - 3V - 0.129V = 0.721V. Power dissipated = 186mW)
Efficiency = 774/993 = 78%

In example 5, the cct would drop out of regulation when the battery voltage drops another 0.22V (or 3.63V) (Efficiency = 83%)
 

Gazoo

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I would think that would be much easier on the battery too. It does give us something to think about. So many mods that can be done to this baby. If Daedal finds out the LD he has ordered is a single mode, I would replace the diode with it and find a better driver. It is a shame there isn't an easy way to connect the batteries in parallel.
 

chimo

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Here's what happens to a CD case when the current is cranked to 258mA.

Focus ~ 6 inches.  No additional lens.

 

Gazoo

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That's some decent power... ;D How long did it take to burn the hole and to burn the oblong hole? And where the hole burned through on the left, did you move the beam around or is that how big a hole it made holding the beam steady?
 

chimo

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Gazoo said:
That's some decent power... ;D How long did it take to burn the hole and to burn the oblong hole? And where the hole burned through on the left, did you move the beam around or is that how big a hole it made holding the beam steady?
The big hole is from after cranking up the current.  I hand-held the laser so that kind of explains the odd shape. I didn't time it, but I would say it took less than a minute.

The other, narrower diameter ones were done with an additional focusing lens.  

Now, using a focusing lens, it takes about 3 seconds to burn a pin-hole through the case!

Paul
 

chimo

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This one was done with a focusing lens.  Time was around 25-30 seconds.  I stood the CD case up and slowly rolled the laser along the surface.  Nice straight burn on that one!

 

Gazoo

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Thank you. I wanted to see if I could do the same with the GB diode. I am only pushing mine to 200ma's until I get my next batch. It only took a few seconds to burn a pin hole in the CD case unaided. This was from a little less than a foot away. I haven't managed to burn an oblong hole, I will try later.

The plastic lenses that come with the Aixiz modules are what I think is making the difference as far as burning things unaided.
 

Gazoo

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I give..I can not compete...lol. Not yet anyway.
 

Gazoo

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I checked to see how much current my SenTorch was drawing on slightly used Panasonic batteries. It came out at 300ma's. One of the batteries measures 3.06 volts and the other 3.02 volts. This is with no load so it doesn't really tell us anything. :p

But 300ma's is not going to cause the batteries to explode as long as we are using brand name batteries. Many people doing flashlight mods push these as high as 2 amps and have no trouble...although I would not recommend it. ::)
 

chimo

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300mA, hmm,......

Perhaps I should crank mine up a bit more. I wonder what the others are getting.
 

Gazoo

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I am also curious. Eventually I am going to make some modifications to mine. For one thing, the spring is not straight...this is very minor but when I mod mine I will be fixing it or possibly replacing it.

I also may put a phasor diode in it depending on how that deal pans out. I am not too concerned about the inefficiency of the driver...I guess we can thank the 4.7 ohm resistor for that.

For now I am very happy with mine. I would really like to know the specs of the diode in this thing...although I know we will probably never know. :p
 
H

High_Octane

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Bernhard said:
I really wish that I can put 9mm (T05) diode in there, and do something to increase current feed. This way, I can make cheap 1 Watt IR laser using this as a host...
If you don't mind me asking, Where are you getting these 1w LD, and what do they cost?
 

Kenom

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