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I have a 15 led 0,5m led strip (ws2812b). Since it's such a limited amount of leds, I'll try to power the strip with an old phone power adapter (5v / 750mA). I looked at the ws2812's data sheet and it says

Each RGB LED draws approximately 50 mA at 5 V with red, green, and blue at full brightness

So that's 15 x 50mA = 750mA

I'll call that one tight, but won't it be all right because these leds are never gonna run full power all the time.

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  • \$\begingroup\$ So what is your question? The fit is tight so watch out for steep voltage drops. \$\endgroup\$ – Maxthon Chan Dec 23 '14 at 12:55
  • \$\begingroup\$ My question in fact, is whether it's "safe" to use that adapter. And is full brightness (red full, green full, blue full) producing a white light? \$\endgroup\$ – jelledb Dec 23 '14 at 13:13
  • \$\begingroup\$ depends how the LED string is set up, are they three different colours or are they just "white" lights? If it's R and G and B, I don't think it will make a proper 'white' result, those LEDs use special filters and materials to get the white result. \$\endgroup\$ – KyranF Dec 23 '14 at 14:00
  • \$\begingroup\$ also the construction of the charger may have current limiting in it, which is good. And if it's rated at 750mA, it should be able to draw that 'forever' and be safe. \$\endgroup\$ – KyranF Dec 23 '14 at 14:00
  • \$\begingroup\$ It are RGB leds and they draw 750mA at full capacity. So normally it will work I hope \$\endgroup\$ – jelledb Dec 23 '14 at 17:38
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This, you will have to try. Try run it full brightness for a while and if your phone charger get hot or the voltage drop is steep, you may need another power supply.

Cheap phone chargers capable of 1A is quite common out there now. Look those up.

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  • \$\begingroup\$ This is what I found about the voltage drops of the WS2812b ledstrips... "The 30 LED 1 m strip drew 1.5 A and had a voltage drop of 0.2 V". So I maybe if I avoid full brightness a bit my supply would be fine. \$\endgroup\$ – jelledb Dec 23 '14 at 13:18
  • \$\begingroup\$ @jelledb You need current limiting resistors! \$\endgroup\$ – Maxthon Chan Dec 23 '14 at 13:23
  • \$\begingroup\$ I was thinking the same. But I'll have another look and check if it's 0.2V / led or for the whole strip. I assume it'll be those 0.2V / led \$\endgroup\$ – jelledb Dec 23 '14 at 13:31
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I think the LEDs can run full power if you want "white colour full power", this is the combination of R+G+B

Now, sinking full power from your power supply can result in various scenarios:

  1. Most likely the PS will show a not so good load regulation and the output voltage will decrease, decreasing the current demand in the LED and finding an "equilibrium". Example 4.8V and the LEDs at full power on 4.7V will only sink 710mA (just an example)
  2. If the power supply has an over current protection (below 750mA) the circuit will switch OFF and ON periodically.
  3. Other... I mean, the PS can be labelled with a power ratings but this can be far away from the truth with lots of low quality PS.

Just try it. If it doesn't work, some solutions could be:

  • If you are driving the LED yourself, don't drive all of them at 100%
  • If the LED are driven by other hardware you can't change, just add a resistor in series with the LED strip to decrease the current demand.
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  • \$\begingroup\$ Thanks! I'll have full control over my ledstrip because I'll drive it with an MSP430 microcontroller. I can programatically limit the max rgb values to 200 for instance (just an example). Doing so I can save my PS. So if I read the answers, "trial-and-error" will be the way to go" \$\endgroup\$ – jelledb Dec 23 '14 at 14:07
  • \$\begingroup\$ Do I need to use resistors or are they built in the led strip? \$\endgroup\$ – jelledb Dec 23 '14 at 17:36
  • \$\begingroup\$ 5V 50mA I would say it has already the resistor inside. \$\endgroup\$ – Raul M. Dec 23 '14 at 17:55

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