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Topic: how much current does an smd5050 rgb led draw at full white brightness. (Read 6199 times) previous topic - next topic

Qdeathstar

http://cdn.sparkfun.com/datasheets/Components/LED/5060BRG4.pdf

I tried looking at the data sheet, and it looks like it says 20mA, but is that for ecan color, for 60mA total for each led?

the reason I want to know is that I am powering ws2801 12v strips with 48 leds/m and need to calculate what my power requiremens will be.
A creaking creeping shadow
stiff against the freezing fog
glares at a tickless watch.

Time has failed him -- all things shall pass.

CrossRoads

You should plan on 60mA for each WS2801/LED set.
If all sets will be full white together, then 60mA * number of LED is needed.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Qdeathstar

on this strip, three leds are connected to one ws2801.

so, for a meter... with 48 leds/m and 16 pixels/m


that would be

60ma x 48leds = 2880mA?

or

60ma x 16pixels = 960mA


A creaking creeping shadow
stiff against the freezing fog
glares at a tickless watch.

Time has failed him -- all things shall pass.

CrossRoads

WS2801 are 5V parts, the LEDs are 3.8V Max rated. How does the 12V come into play?
Are there transistors involved also?
The LED you linked to is 3 LEDs in one package. Are you saying there are 3 packages connected to each WS2801? If so, how are they wired?
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

CrossRoads

When LEDs are connected in series they share the current.
So 3 RGB LEDs with discrete LEDs in series are 9 LEDs total - yet just 60mA are drawn, 20 for each 'string' of 3 LEDs.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Qdeathstar

one these strips, the leds run of 12v and there is a ziner? diode that drops the voltage to 5v for the ws2801 chip.


so, three SMD 5050 rgb modules are hooked up to each ws2801 chip.

and that is 9 LEDs total? r x 3, g x 3, b x 3?

so that is 60 mA for those 9 LEDs, and 60mA for the three smd5050 led modules
A creaking creeping shadow
stiff against the freezing fog
glares at a tickless watch.

Time has failed him -- all things shall pass.

Qdeathstar

A creaking creeping shadow
stiff against the freezing fog
glares at a tickless watch.

Time has failed him -- all things shall pass.

Grumpy_Mike

Quote
and that is 9 LEDs total? r x 3, g x 3, b x 3?
If there are three LEDs in series then they take the same 20mA current so for 3 RGB LEDs you need to allow just 60mA.

Qdeathstar

Ok. So just so if I under stand


12v+ ---- RedrgbLEDpin ------ RedrgbLEDpin ------ RedrgbLEDpin ---- resistor ----- gnd === 20mA

12v+ ---- BluergbLEdpin ------ BluergbLEdpin ------ BluergbLEdpin ----- resistor ----- gnd === 20mA

12v+ ---- GreenrgbLEDpin --- GreenrgbLEDpin ---- GreenrgbLEDpin ---- resistor ---- gnd === 20mA

20mA For all of the red pins + 20mA for all of the blue pins + 20mA for all of the green pins is 60mA for all three RGB leds??



A creaking creeping shadow
stiff against the freezing fog
glares at a tickless watch.

Time has failed him -- all things shall pass.

Qdeathstar

A creaking creeping shadow
stiff against the freezing fog
glares at a tickless watch.

Time has failed him -- all things shall pass.

CrossRoads

Reply #8, that will not work. Each LED has some voltage drop across it - 3 LEDs needs 10V or more to turn them all on.
See figure 8 of the WS2801 datasheet. An external transistor is needed for the higher source voltage.


Power is Voltage times Current, P=IV.
Say you had LEDs with Vf of 3V (their turn on voltage) and you allowed 20mA to flow.
3 LEDs in series can "share" the same current, but need higher voltage. P = (3 x 3V) x 20mA = 180mW
3 LEDs in parallel can "share" the same voltage, but each will draw 20mA. P = 3V x (3 x 20mA) = 180mW
So the power used is the same. In 1st case, 20mA supply is needed. In 2nd case 60mA supply  is needed.

Higher voltage supplies can be easier to find than higher current supplies, and be physically smaller.
So for example a 12V 1A supply can drive 50, 3 LED strings at 20mA each. 150 LEDs are being lit up.
While a 5V supply driving 1 LED strings would need 3A to drive those same LEDs in parallel.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Qdeathstar

I'm sorry, I meant 12v.


That makes more sense now.. You are still using the same amount of power(watts), you are just using higher voltage and lower amperage, which is the reason I wanted to use 12v to start with.. I just forgot in the context of this conversation.
A creaking creeping shadow
stiff against the freezing fog
glares at a tickless watch.

Time has failed him -- all things shall pass.

Qdeathstar

So,  I decided to test this out for myself using my DMM and it seems like every three LEDS draws right around 92mA

Does that sound OK?

I tested it by taking the ground wire off, the strips, and putting one of my leads on the strip, and the other on the ground wire, under the "200m" setting, and it read right around 92.. so i'm assuming that is 92mA
A creaking creeping shadow
stiff against the freezing fog
glares at a tickless watch.

Time has failed him -- all things shall pass.

Qdeathstar

I measured the resistance across the led strip's resistors and I got an 340ohm resistor for the RED leds, and 140ohm for the blue and green leds. They are wired in series.
A creaking creeping shadow
stiff against the freezing fog
glares at a tickless watch.

Time has failed him -- all things shall pass.

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