Stable 12V from auto for LED strip? Or (hopefully) better approach?

Discussion in 'General Electronics Chat' started by MythicalCoder, Aug 29, 2015.

  1. MythicalCoder

    Thread Starter Member

    Aug 28, 2015
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    I have a set of four 12V RGB LED 5050 SMD strips. The seller I bought them from was clueless about what kind of LED's were used, and (essentially) told me to keep it connected to the controller box. I do not want to do this however as I'd like to have two different colors shown simultaneously, something the controller doesn't support. Additionally, they told me it requires a stable 12V, and since I'm using it in a car, this is not possible directly. I suspect there are already current-limiting resistors built into the circuit in the typical fashion for these 12V strips. While I don't see any on the LED side, I suspect they exist on the backside which I cannot see.

    All this in mind, I have a few questions:

    1) Would these LED strips even work on lower voltages (say, 5V), assuming I had a high enough mA to power them?

    2) If not, how do I go about "stabilizing" the wide voltage range of an auto (I was reading it was something like 9V to 60V) to the voltage that the LED strip supports? Linear regulators like the LM7805 work well for bringing a higher voltage down to a lower one, but beyond a dedicated module (like the XL6009 ones on eBay, which are clunky at best), I'm not sure how to conditionally bump the voltage up or turn it down (or if I even need to).

    3) Currently I'm using an Arduino with a bunch of transistors and 220 ohm resistors to control the color of the LED strips via PWM. It works, but relies on the XL6009 module being precisely tuned, which, as stated, is clunky at best (it relies on a small screw adjustment). Is there a better way for PWM'ing these strips without using a 555 timer like the prevailing Google result suggests? I tried the 555 timer approach first, and found it to be wholly user-unfriendly. Is there a chip that can PWM the LED's at the required voltage without using external transistors? Only need PWM for two of the pins if it helps (it's only using white and amber, the two amber ones require the PWM).

    I've googled high and low for days for the answers to my conundrum, so I finally decided to just ask people who know what they're doing :)

    Thanks in advance!
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Welcome to AAC!
    An appropriate DC-DC converter could give a stable 12V, but it would be advisable to include transient suppression components on the input to catch any load-dump spikes on the +ve rail. Since different coloured LEDs have different forward voltag drops (Vf) the controller must be allowing for that somehow. If you abandon the controller you will probably have to provide suitable current-limiting resistors for the individual colours.
     
  3. MythicalCoder

    Thread Starter Member

    Aug 28, 2015
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    0
    Thanks for the warm welcome, and for the helpful response!

    This got me curious, so I decided to open the controller to see what's inside, thinking it might provide some insight. Here's the pictures I snapped (which I tried to make as clear as possible):

    20150829_101129.jpg
    20150829_101201.jpg
    20150829_101310.jpg

    From my amateur perspective, it appears that the common anode is fed the 12V directly (through the black wires, conveniently color-coded), then the grounds (red, blue, and green wires) are simply switched by a transistor connected to the bigger chip. So it doesn't appear that there's any kind of resistor built into the controller at least, which means it's built into the LED strip already. So it looks like I'm stuck requiring an exact 12V power source.

    This seems to be the best approach in my scenario. How do I select an appropriate DC-DC converter and the accompanying transient suppression components? Also, is there any way to outsource the PWM job to another chip instead of putting the timing burden on my Arduino?
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    You want one which will accept 12V (give or take several volts) input and can be set to give 12V out (here are some examples). Googling for 'TVS diode' should find you some suppressors. You'd need one with a standoff voltage ~15V and a clamp voltage less than the maximum input voltage specified for the converter.
     
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