Old 01-20-2011, 02:03 AM #1
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Default having issues with 317 driver

Another member on this forum has been very helpful, but he too can't figure out what is going on. I built a standard LM317 driver, cap size is 10uF, resistor size is 47ohms, input voltage is a 9v battery.

Test load consists of 6 diodes in series with 1 ohm resistor, checking the mA (mV) across the resistor.

Circuit fires up fine but I am reading 400mA across the load resistor. The voltage reg. is warm, but not to hot to touch. It drops rather quickly from 400mA to 308mA where it sits and then slowly looses 1mA every few seconds which I assume is from battery depletion.

So....what is going on? I am shooting for a load of ~30mA to drive a Blu Ray diode. Obviously even 300mA will toast it. According to the calculator posted here, a 47ohm resistor with the LM317 would yield around 30mA. Help appreciated!


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Old 01-20-2011, 02:45 AM #2
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Default Re: having issues with 317 driver

Have you tried using your meter in amp mode, in series with the test load?
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Old 01-20-2011, 02:55 AM #3
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Default Re: having issues with 317 driver

ok i figured it out. Apparently I had the Laser diode wire (positive) coming out of the ADJ instead of the Vout. Swapped it over one, now reading 28.7mA The wiring diagram I have for this circuit isn't very good and it looks like everything is soldered in one big bunch on the positive side, but now I realize your LD wire must connect after the resistor and capacitor.
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Old 01-20-2011, 05:03 AM #4
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Default Re: having issues with 317 driver

Here is a visual LM317 driver diagram for Blu-Ray:


Your 47 ohm resistor allows less current.

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