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I decided not to order / use the power supply typically sold with SMD 5050 kits. I heard a lot of explosion stories regarding those dodgy stuff.

I want to make my own (power supply to drive SMD 5050. Using: a DC adapter found at home hooked up to LM2596 converter.

Facts:

  • From what I gather, LM2596 regulates the voltage AND can supply 1 to 2 amps of power safely (more requires heatsink?).

  • A single SMD 5050 chip uses 0.24 w of power.

  • SMD 5050's run on 12v.

My question:

  • Is it safe to assume that I can connect any number of LED strip blocks (with each block having 3 LEDs each using 0.24w, therefore ~0.75w), as long as total amps do not exceed what LM2596 AND power adapter attached to it can supply (being max 2 amps)?

My calculation:

watt = amps x volts means each LED uses 0.02 amp.

So if I have 30 blocks == 90 LEDs.

90 * 0.02 = 0.6 amps.

  • Would it work fine?

  • And if I just connect a single block needing 0.02 amp, would it still work fine?

  • What would happen if I connect more LEDs and exceed the amps LM2596 can provide?

I don't want my leds burning in day 2 and learn about this subject.

I'd very much appreciate it if all questions were answered.

Thank you!

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  • \$\begingroup\$ What is the point in having a DC adapter followed by DC/DC converter? Yes, the cheap ones supplied with LED strips are crappy, but you can just replace it with a good quality one. \$\endgroup\$ – venny Sep 1 '14 at 0:08
  • \$\begingroup\$ And LM2596 is somewhat dated these days. \$\endgroup\$ – venny Sep 1 '14 at 0:24
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    \$\begingroup\$ I have DC adapter that is not 12V and LM2596 looks cool and cheap and I want to experiment (in building stuff) and learn (without wasting money by frying circuits), that's why =) Would appreciate a full answer please! Thanks. \$\endgroup\$ – Phil Sep 1 '14 at 0:30
  • \$\begingroup\$ Is the voltage of the DC adapter higher or lower than \$12\, \mathrm{V}\$? \$\endgroup\$ – venny Sep 1 '14 at 1:07
  • \$\begingroup\$ I think I've got both. There are several of them lying around and I remember seeing 24V as well as 5V ones. \$\endgroup\$ – Phil Sep 1 '14 at 1:19
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LED strips work at \$12\, \mathrm{V}\$, but the individual chips do not. They are connected in groups of three with one series resistor. Voltage drop of one LED is around \$3.6\, \mathrm{V}\$, so the current is \$\dfrac{0.24}{3.6}\cong 65\, \mathrm{mA}\$. For 30 blocks, it is \$30\cdot 65 \cong 2\, \mathrm{A}\$.

LM2596 is quite ancient, you could do better with something like TPS54340 or even better, with synchronous buck regulator likeLT8614. Newer chips have higher switching frequecies, which means that you can use smaller inductors with fatter wire and also smaller capacitors.

With only one block attached, it will work just fine (although less advanced regulators will have lower efficiency).

If you connect too much LEDs, you will overload and overheat the regulator and it will employ its overtemperature protection.

Edit: LEDs are grouped by 3 like this:

pic

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  • \$\begingroup\$ venny thanks for the answer! this is bit confusing however. if a whole strip consisting of 100 blocks is at 12v, how can a single block be at 3.6 V? is there a simple way to understand / grasp this overall? - BTW when I said LM2596, I meant something like this (whole circuit) ebay.com/itm/…. \$\endgroup\$ – Phil Sep 1 '14 at 1:24
  • \$\begingroup\$ @Phil Blocks are at 12V, individual LEDs are at 3.6V. See added picture. \$\endgroup\$ – venny Sep 1 '14 at 1:39
  • \$\begingroup\$ btw forgot to ask - have you got any PSY recommendations? \$\endgroup\$ – Phil Sep 1 '14 at 8:34
  • \$\begingroup\$ @Phil The LEDs have a forward voltage drop at their rated current, of ~ 3.6V but really you should test this one one of the strips. The resistor is then just acting as a current limiter, and also is not very constant over temperature of both the resistor itself and the temperature of the LED chips which over time heat up and draw more current and chew more voltage. \$\endgroup\$ – KyranF Sep 1 '14 at 8:51
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Is it safe to assume that I can connect any number of LED strip blocks (with each block having 3 LEDs each using 0.24w, therefore ~0.75w), as long as total amps do not exceed what LM2596 AND power adapter attached to it can supply (being max 2 amps)?

Yes, but your math is off.

A LED strip has multiple Parallel Segments of typically 3 leds and one resistor in series, per channel. Typically set for ~18mA per channel per segment, at 12V. Since current is shared in series circuits, that means each segment channel only uses 18mA, for all three leds in that series. With 3 channels, that's 54mA for full on, per segment.

Single color 5050 strips are rare, but not unheard of. They still should follow the same setup.

So 30 Segments is 90 Leds, per channel, but since each channel/segment/series pair share the current, it's still just 30 "blocks" of power. But 3 channels, its 90 blocks of power.

Your LM2596 should work fine with just one 20mA segment. Anything more than it's maximum current draw OR the recommended heat buildup, it's protection should kick in:

Self protection features include a two stage frequency reducing current limit for the output switch and an over temperature shutdown for complete protection under fault conditions.

BUT! Depending on those protection features to limit the current or not properly heatsinking, is BAD ENGINEERING and can lead to fire. At best, you burn out the regulator or inductor, at worst, you need a new house. Don't over load it.

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  • \$\begingroup\$ thanks for the answer! I'm mostly interested in getting a "white" color. Would a "white" strip or RGB set to give out white would provide more bright light? And have you got any PSU recommendations? Thnx again! \$\endgroup\$ – Phil Sep 1 '14 at 8:34
  • \$\begingroup\$ @Phil go straight for white LED if you can. It would most likely be poor efficiency for an RGB LED to try to produce equivalent "white" light (which is mostly blue and a bit of green and red thrown in) \$\endgroup\$ – KyranF Sep 1 '14 at 8:53
  • \$\begingroup\$ @KyranF I (!) just discovered SMB 5060s =) Super bright, pure white! Shall try them. Thanks! Now onto finding a good power source that won't start fires in the kitchen. \$\endgroup\$ – Phil Sep 1 '14 at 12:52

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