testing LM317 driver

[stackingmont]

i just did some repairs on my diode driver, and i want to test it. my diode is in the mail. sadly, i don't have a multimeter and i trashed my burnt diode in the process of getting it out of the module, so i decided to use a regular flashlight bulb. when i connect it, it does not light up. i was wondering if this is normal and if anyone has any other suggestions to make sure that my driver is at least conducting electricity.

 

[xanatos]

Yup, simple - using a 1-ohm resistor and 4- 1N4001 diodes, all in series. Complete details have already been covered here:

http://www.laserpointerforums.com/forums/YaBB.pl?num=1190170289

Measure current by measuring voltage drop across the 1 ohm (mV = mA) and read V to the diode by reading V across the 4 1N4001 diodes. Look at the instructions/diagram and you'll be all set. I've built a few of these units, complete with heat shrink, for testing. Only used one once to test if IT worked, and it does. Happy testing!

Dave

 

[stackingmont]

but would the current be enough to light up the flashlight bulb?

 

[xanatos]

Current delivered to a resistive load is a function of the resistance of the load. The LM317 will deliver what current you set it to for an LD, which will take (for example) 250mA at around 3v. If the resistance of the lightbulb is higher than a given amount, the voltage across it will not be sufficient to push the current necessary to drive it to incandescence. In short, probably not! Measure the voltage across the bulb just for fun, but if you're serious about being sure it's going to work, nothing like making the right tool for the job.

Dave

 

[stackingmont]

k thanks, i just picked up a green led from radioshack and it does seem to have similar qualities voltage wise as the LD. i also got a project box to put it all in. I can't wait till the LD comes!

 

[rog8811]

If you are considering doing more laser building I would seriously suggest that you get yourself a digital multimeter, they are pretty cheap but invaluable for checking your circuits before connecting an expensive LD. It takes all of the finger crossing out of final connection

Regards rog8811

 

[stackingmont]

well you're right, but in this case i already know it will work because i've used this same driver to drive a diode before, but the diode burnt out from a discharge of the cap after being briefly disconnected. ill look into a multimeter. do u know if they have them at radioshack?

 

[xanatos]

Yes, RatShack has a few meters. I actually have one, works pretty good.

Dave

 

[stackingmont]

cool ill go look at em. i live like a mile away from a radioshack, so i practically live there.