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 Laser Pointer Forums - Discuss Laser Pointers Driver test load confusion`

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10-05-2011, 11:58 PM #33
 Class 4 Laser Join Date: Dec 2010 Posts: 8,491 Rep Power: 1392
rhd
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Quote:
 Originally Posted by sassafrass686 It looks like the operating voltage is 3.7-4.5 DCV, so I don't understand why I would need any diodes on a test load since my battery only supplies 3.7 volts.
Battery is irrelevant. Your test load attaches to the driver output, not to the battery. A test load has no idea what battery is attached to the other end.

(a) Voltage you need the test load to drop
= 445's Vf at your current (say 1.8A)
= 4.8 V (roughly)

(b) Voltage your 1 ohm resistor will drop
= Current x Resistance
= 1.8 x 1
= 1.8 V

(c) Voltage left for your diodes to drop
= a - b
= 4.8 - 1.8
= 3 V

(d) Number of diodes you need

** So, check the datasheet for your diodes. How much voltage do they drop at 1.8A ? Let's say they drop 1V when run at 1.8A **

= 3 / 1
= 3 diodes needed

Someone should check my presumptions / math. I'm really tired and my brain is foggy.

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Last edited by rhd; 10-05-2011 at 11:59 PM.

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10-06-2011, 01:36 AM #34
 Class 1M Laser Join Date: Jan 2011 Location: Dallas Texas Posts: 110 Rep Power: 14
sassafrass686
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Awesome! I appreciate all of your help!
Thank you much.
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10-06-2011, 01:57 AM #35
 Class 3R Laser Join Date: Sep 2010 Location: wv Posts: 1,389 Rep Power: 152
benmwv
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Quote:
 Originally Posted by jimdt7 Yes the schematic is correct ! You must connect your diy driver leads where the blue-ray should ! Also at 1,25A the lm317 will get very hot ! Do you have a heatsink for it ? I recommend you to use an lm350 which has maximum of 3A so you wont need heatsink at all !
This ^^ has been nagging at me since I first saw it.

Just because an lm350 can handle 3A doesn't have anything to do with the amount of heat it produces. They will both be to-220, at the same current, same load, and same input voltage. Therefore the heat produced will be exactly the same, and they will need the same amount if heatsinking.

Their max current is irrelevant.

10-06-2011, 05:20 AM #36
 Class 1M Laser Join Date: Jan 2011 Location: Dallas Texas Posts: 110 Rep Power: 14
sassafrass686
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Posts: 110
Rep Power: 14

Ahaha. Just got home from work and assembled the load. I tested it with a linear driver (as I'm waiting for the buck driver to come in the mail) and it works perfectly! Thanks again for all of your help rhd.
+rep
__________________
• 5mW 635nm keychain
• 40mW 589nm PGL-III-C
• 5mW 532 pen host
• 130mW 532 Icon Rogue Host AWESOME!! **See it HERE**
• 230mW 473nm DOHM-M-473
• 1.7W 445nm Kryton Groove
• 700mW 445nm Sirius1-C
• 2.5W 445nm Mace of Doom
• 35mW 405nm pointer (from China!)
• 65mW 405nm E3 from Wicked Lasers

 Tags circuit, driver, dummy, load, test

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