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Voltage problem with circuit

paper183

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I made deadal's current regulating circuit for my gb diodes, and i have a weird problem, the diode only receives ~2.3 volts :-/ the amps are okay, the pot i'm using is a 50ohm multiturn it was set at 7,6ohm which gives 165ma to the diode (1.25/7.6=165ma and i measured it), the diode lights but it's very dim... i tried different voltage input ranging from 6v to 9v and the diode always receives 2.3v. To get the voltage reading, i used 3x 1n4001 diodes in series. When i first tried it, it read 2.7v and my batteries were low, the diode was lighting like it should, it went dim but i don't think it's broken since now the circuit feeds it only 2.3v... Could some part of the circuit have been broken or something ?

here are some pics of my circuit: http://s216.photobucket.com/albums/cc31/paper183/DIY lasers/
 



Benm

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You could have burned out the pot.. it's rated power is only over its full resistance, and considerably lower for the 7.6 portion of a 50 ohms pot. The LM317 is pretty bulletproof.
 

Daedal

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That looks like it's wired right... I would check the components or the supply. :-?

--DDL
 

paper183

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tried different supplies, 4xAAA, 1x9V battery and a 6.8v wall adapter...
 

Daedal

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All are giving you ONLY 2.3V?? :eek:

I think something's wrong with the LD if that's the case... :(

Try lowering the amps a bit and use something else just to test it out... do you have one of the AixiZ laser diode that come inside the modules? Try one of these out... ;)

--DDL
 

paper183

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i get 2.3v with my dummy (3x1n4001) the diode from the module is broken. I'll lower the amps and get the reading with the ld...
 

Daedal

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OH!!! ;D ;D

Ok.. your circuit is working fine then. ;)

3 X 1N4001's will take about 2.1V, put 4 of them and you should notice a 3V drop. This thing will power up a GB diode ;)

GL;
DDL
 

paper183

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ok so my diode went dim :\ :( got another one, i have no idea why it broke tho :(
 

BlueFusion

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Changing input voltage shouldn't affect output voltage. If it does, the LM317 is SERIOUSLY fried.
 

Gazoo

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paper183 said:
i know what killed it, i used 6,8v as input voltage :(
Make sure the capacitor has no voltage in it when you hook up the new diode, short the capacitor to get rid of the voltage with the power off. The only other thing I can think of is did you have the diode hooked up before you applied power or measured current? If you apply power to the circuit the capacitor will charge up to a high voltage, so if you then hook up your diode it will most likely die.
 

Daedal

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The LM317 is not regulating voltage, it's regulating the current. All it does is drop the voltage by 2.5-3V

--DDL
 

Gazoo

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I did a test to confirm what I was already certain of. I powered my LD with 160ma's of current. The voltage across the capacitor was 2.51 volts. Then I removed my LD from the circuit and rechecked the voltage across the capacitor. It was 5.8 volts..almost the same as my input voltage of 6 volts.

Once I disconnected power, the voltage of the capacitor dropped quickly. But to be safe I shorted it then reconnected my LD. So my point was, if one connects the LD after applying power to the circuit, the voltage stored up in the capacitor will probably kill the LD.
 

Daedal

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Good point Gazoo. This really can never get enough reiterating. I honestly suggest soldering the Cap right onto the LD for this sole purpose ;)

--DDL
 




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