Help with multi LM317 in parallel

[dethlore]

Give them a break. Resistors are expensive.

oh, wait...

So if the LEDs are in a 3 in series, multiple in parallel, it's ok as long as each series has a resistor to protect that mini strand?

 

[dethlore]

It's a great opportunity to stock up on parts too. I especially like those quantity deals where the quantity price breaks are actually less than 50% of the previous price like this. Just $9 for 1000! Less than 1 cent per resistor! They used to charge me 5 cents for two at the labs!

I have been ordering all my electronics pieces from this place. Resistors usually are already a penny a piece, no bulk necessary.
1.2 OHM 1/4W 5% Carbon Film Resistor

 

[Bionic-Badger]

Cool, I'll have to remember that site. Though buying in bulk might just be an excuse for me to get a bunch of resistors.

 

[Bionic-Badger]

Another thing you may consider is to just buy an LED driver so that you change the brightness as you want. For example, you can use the TLC5940 driver chip and modulate the brightness with its 12-bit PWM.

Also with regards to the LM317: unless you REALLY have a power supply that is erratic, you might just forego the voltage regulator and use the LEDs and current-limiting resistors directly. Most switching power supply wall warts are pretty stable as-is, and voltage instabilities will be spread across many LEDs and the resistor. Plus, you can fit in another LED or two on the strand since you won't need 3-4V for the voltage regulator itself.

Also make sure that your current-limiting resistors match the overall forward voltage drop of the LEDs you're using in the particular strand. Some have voltage drops as low as 1.7V each, others maybe 2-3V. If you're using a driver like the TLC5940, where you don't use current-limiting resistors on each strand, you can put regular diodes in series to drop voltage if needed.

 

[dethlore]

I was thinking of using a PC PSU which are very stable, so I'm thinking I may not need the LM in the circuit at all... just a good pot and the resistor->LED->LED strings in parallel should be ok.

just wonder if those RGB led strips can be controlled separately with one control box or if I need 3 different boxes... ? Anyone know?

 

[Bionic-Badger]

I think the box has to be made for RGB and have 3 channels.

 

[Things]

All the RGB LED strips I've had have a resistor for EACH LED. Only 1 resistor for the entire string is stupid.

If you buy the one I linked back, it has individual resistors per LED. You can hook a few strips up to the same controller, but be careful of the current. Each controller can handle about 15 metres total.

You will need 1 controller for each string if you want to be able to change all their colours separately. You can buy the controllers separately for about $3.

 

[dethlore]

I think I'll just get the one controller for now and eventually play around with making some sort of custom controls out of an arduino and PWM

Thanks for the input everyone.