LM317 vs 7805

[Sefrez]

I see all the DIY tuts on red lasers are using the LM317 chip. Would the 7805 work too?

 

[.3lite]

yes of course, but with for example 20 ohm resistor for 250mA.

 

[ben74]

Whats the 7805 chip and its advantages?

 

[JLSE]

Whats the 7805 chip and its advantages?

I dont think it has any advantages over the 317. Its a voltage regulator, which works fine with lower output diodes but allows the current to increase as the diode warms up (thermal runaway). The 317 can also be used as a voltage reg. but you want the current controlled and steady not the voltage. I have used both and would definately recomend the 317 over a 7805.

 

[rog8811]

I echo wannaburns post, the 7805 is no good in CC confuguration, It is ideal for PS3 blu rays as a CV driver, I would not recommend it for anything else.

Regards rog8811

 

[Sefrez]

Oh well.. I was at radioshack so I when ahead and got one lol. Now I have both.

So I should use the LM317T for red diodes, and the 7805CT for blue ray?

 

[Hemlock_Mike]

I use a 5 volt LDO cv regulator in both of my 6x BluRay lasers. Just add a series pot for current limit and a 1 mA dummy load resistor to protect the diode from the capacitor.

Mike

 

[JLSE]

Oh well.. I was at radioshack so I when ahead and got one lol. Now I have both.

So I should use the LM317T for red diodes, and the 7805CT for blue ray?

It depends which type of bluray diode youre reffering to. If it the lower power PS3 diode, then yes. If its for an 803t or 6x, not a good idea. Unlike the PS3 diodes the 803t and 6x diodes heat up, the diode draws more current as it heats up. One way around this with the 7805 is to set the current to say, 80ma on a diode that could handle 100+ma. But either way you have to babysit