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blu ray driver not putting out enough mA






That's fine. When you're measuring voltage where the diode should go, but without a dummy load, the circuit will show almost the supply voltage. Like any semiconductor device, at a very low current, the LM317 will have a very low voltage drop.
Now we need a proper dummy load. Do you have a few leds? If so, what kind? If not, do you have an extra 100 Ohm resistor?
 
i have plenty of led's. a bunch of high entensity ones, and the old school standard ones


also a bunch of 47 ohm resistors and some 10 ohs, putting those in series would be roughly 100 ohms
 
yep, i have 4 greens, set them up. should i go at it?

just powered it up. 3.9 volts going across the led's. they are shining great
 
See if you can turn the brightness from very low, to very bright. At the same time monitor the voltage drop across the LED pack.
___LED___LED___
-----<___LED___LED___>-----

^here and here^


Can you adjust the brightness?
 
oh yes, big difference. 4.66 volts when pot is at lowest resistance, 3.92 volts when pot is at its maximum resistance
 
Looks like you're ready to try that BluRay. Start by disconnection the batter, then short out the capacitor, now wait 15 seconds and short out the capacitor, then short out the capacitor ( I promise I'm not just being funny) turn the pot to max resistance, now connect the LD, and finally the battery.

Then slowly turn down the pot until it reached laseing threshold, then disconnect the battery. Mark the position of the pot, measure the resistance across the pot and fixed resistors, and post here! ;D
 
how exactly will i know what the lasing threshold is?? do i just need to make best judgement? ::scared::
 
Oh, you'll know.
It will go:
dim, so I'll turn it up a little
still dim, so I'll turn it up a little
a little brighter than dim, so I'll turn it up a little
just a tiny bit brighter, so I'll turn it up a little
AHHHHHHHHHHHHHHH!!!!!!!!!!! IT WORKS!!!!!!! HAPPY DANCE!!!!!!!!
^That will be the threshold. ;)

Use a piece of A4 paper as a target.
 
i just turned the pot up to max-62mA thru diode, sitll never dimmed. should i leave it at that?

ps that was mighty bright compared to my other one with just a resistor(sigh) and cap on 6v.
 
busterhax said:
i just turned the pot up to max-62mA thru diode, sitll never dimmed. should i leave it at that?

ps that was mighty bright compared to my other one with just a resistor(sigh) and cap on 6v.
Click to expand...


Sorry, I don't understand. you started with the pot at max resistance, and slowly turned it to lower the resistance, but the LD output didn't seem to change?
 
oops sorry. no. i started at max resistance, as i turned the pot down, it got brighter and brighter. it never dimmed like you stated. i reached the lowest i could on the pot and it still never dimmed, just very very bright. there was 62mA going through the diode. should i stop there or should i keep playing with the resistors until i find the threshold?
 
Sorry I confused you. It should have gotten suddenly brighter, not dimmed.
leaving the pot where it is, can you measure the voltage drop across the resistor and pot. Make sure it's 1.25V
 
voltage drop was 1.14 volts.
i thought you were saying to keep turning the pot down until the beam suddenly went from bright to very dim, then turn it back again until it was suddenly bright again. i guess should i keep running it at 62mA? that seems pretty dangerous compared to other setups
 
Saved by low battery voltage again! If there is not 1.25V difference between the Vout and Adj pins, the regulator is dropping out.

I think what confused you was my saying 'turn it down' instead of 'reduce the resistance of the potentiometer' Again I am sorry, but glad that no damage was done.

What battery are you using? a PP3? If so, turn the pot to the max resistance, then change the battery.
 
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