0
\$\begingroup\$

My first post here, please keep in mind that I hardly know anything about electrical engineering so please keep any replies in layman terms, thank you!

I bought this 30cm white LED strip.

It's set up to run from 12 volts. The thing is I would like to use it at 6 volts. I can see that there are soldered IC chips on it: an M7 chip and a 78L05 chip; from what I could find out the 78L05 chip is a voltage regulator.

What would be the simplest way to get this to run from 6V?

\$\endgroup\$
6
  • 1
    \$\begingroup\$ Hmm, perhaps post a picture of the circuit (pcb). (Both sides if there are copper traces or components on both sides.) \$\endgroup\$ Sep 18, 2014 at 12:47
  • \$\begingroup\$ Here's a image, the 78L05 is second chip from the left drive.google.com/file/d/0B7Zjegs8UFKRcEJaMFdjRnhmVzg/… \$\endgroup\$
    – John Doe
    Sep 18, 2014 at 12:56
  • \$\begingroup\$ It's not going to happen. The 78L05's dropout voltage is in no case low enought to run from 6V. \$\endgroup\$
    – Matt Young
    Sep 18, 2014 at 12:58
  • \$\begingroup\$ What would be the simplest way to have the the item run on 6v instead of 12v? \$\endgroup\$
    – John Doe
    Sep 18, 2014 at 13:02
  • \$\begingroup\$ OK, hard to tell what's going on. (What's the part number on the other IC?) If you have access to a bench power supply you could try running it from a lower voltage and see what happens. It may be that the LM7805 just sets the voltage for that other IC in the picture. As Matt points out above, it will take at least ~6.5V to turn on the lm7805 \$\endgroup\$ Sep 18, 2014 at 13:06

2 Answers 2

1
\$\begingroup\$

To save the hassle of trying to modify a device to take a different voltage, I would personally consider using a "step-up" or a boost DC-to-DC converter to simply provide the required voltage.

One like this boost converter from eBay would be able to take in 6 volts and supply 12 volts on its output.

Your eBay listing did not provide amperage/power requirements, but the ~10 watts this provides should be enough

\$\endgroup\$
5
  • \$\begingroup\$ The module from the link is boost converter, buck would not help here. \$\endgroup\$
    – venny
    Sep 18, 2014 at 13:36
  • \$\begingroup\$ @venny: Whoops, thankyou for correcting that \$\endgroup\$
    – Al Longley
    Sep 18, 2014 at 14:20
  • \$\begingroup\$ I was just on my way out to buy one of those, luckily I checked here first. Please keep the suggestions coming. :) \$\endgroup\$
    – John Doe
    Sep 18, 2014 at 15:45
  • \$\begingroup\$ would this work? ebay.com/itm/… \$\endgroup\$
    – John Doe
    Sep 18, 2014 at 15:51
  • \$\begingroup\$ Wait a minute... isn't a boost converter what I need here? The leds currently need 12v to run, I only want to feed them from a 6v source, adding a boost converter would let me do just that, correct? \$\endgroup\$
    – John Doe
    Sep 18, 2014 at 16:07
0
\$\begingroup\$

The M7 and 78L05 form a 5V power supply. If your 6V is well regulated you could try putting a diode from input to output of the 78L05, shunting it out of the circuit.

That will reduce the 6V input to a bit less than 5V. However if your 6V supply is 'dirty', badly regulated etc. (or if I miss-guessed the schematic) you could burn out the microcontroller and your gadget will be trash.

If you're prepared to take that risk, you can give it a try.

Edit: This is for 6VDC- the OP has revised to 6VAC so this is not useful answer, see comment below.

enter image description here

If you plug it into anything more than about 6.5V (including the 12V it was originally designed for) it could be destroyed- would definitely be destroyed at 12V.

\$\endgroup\$
7
  • \$\begingroup\$ I might give that a try, I have two backups if anything would go wrong. I bought a boost DC to DC converter and I got no reading at all from the out put on it. I think however I forgot to mention a crucial part, the 6v power source I'm tapping in to is AC, (a pinball machine) Yes, I know I'm a n00b! \$\endgroup\$
    – John Doe
    Sep 18, 2014 at 18:53
  • \$\begingroup\$ If you feed it 6VAC it will not work properly and will likely die! Instead of the diode try adding a 1000uF/16V (2200uF would be better) from pin 3 (+ lead) to pin 2 (- lead). Do not put the diode on there. \$\endgroup\$ Sep 18, 2014 at 18:56
  • \$\begingroup\$ Okay, I see, thank you! Now it's just a matter of finding somewhere to buy that cap. \$\endgroup\$
    – John Doe
    Sep 19, 2014 at 11:05
  • \$\begingroup\$ I installed a 2200uF today and it works just like you said, having said that it was pretty hard to solder the cap to the lm7805. Is there any other point where I could solder the cap too? \$\endgroup\$
    – John Doe
    Sep 30, 2014 at 17:11
  • \$\begingroup\$ There's nothing wrong with extending the capacitor leads with thin wire for an inch or two. \$\endgroup\$ Sep 30, 2014 at 17:43

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.