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Topic: How does this LED work ? (Read 587 times) previous topic - next topic


Jan 15, 2019, 04:21 pm Last Edit: Jan 15, 2019, 05:31 pm by sweeneytate

I am new to electronics. I have a sound activated 10watt LED running through a 5v step up.

The voltage coming out of the booster is around 10.5volts. This LED is 10watts. How is this working with out a resistor. I do not have any resistors and was just testing it out, and it worked......

The booster is plugged into the Vin and to pin 9 (for signal).

The sound detector is plugged into the 5v,GND and pin 2(input signal)

I think the current  is 0.9A.









you need to provide more information on what you mean by the LED - like a link to its product description.

similarly, what booster?

A fast moving video doe snot give us that information.

From what I could see in the video, that LED is not just an LED, it is some module with additional electronics.


I looked the LED up and they are designed to run anywhere from 9-11v depending on which one you have.  There are actually 9 x1 watt LED's on  the chip and I'm guessing they are wired series parallel to drop about 3.2 v each x 3... So you don't need a resistor on a 10V power supply.  

You are outputting more than 0.9mA.  It would not be as bright otherwise.  The way you have it wired with power from Vin is questionable at best.  If it's reverse current through your regulator you may burn it out.
Bad Boys Race Our Young Girls But Violet Generally Wins - Get Some Now :) - ELI ICE man


I think the current  is 0.9mA (although I am not too sure).
More like 0.9 A, if it is  a 10W device...


Do yo have the specs for the LED?

Something  is limiting the current.   A 10W LED actually running at 10W would probably "blind" the camera.   Power is calculated as Voltage x Current so a 10W / 10V LED would be running at about 1 Amp.

I'd guess you are powering the step-up converter from an I/O pin.   If so, that's wrong!  The I/O pins are rated for 40mA maximum so if you are powering the board that way you are overloading the I/O pin and if you measure the voltage you'll probably find the 5V is not holding-up, and that's what's (improperly) limiting the current.   (You'd have to modify your code to hold the LED on while you measure voltage.)

The Arduino I/O pin should drive a MOSFET, or relay, etc., to control  power to the LED, with the power coming from somewhere else.

High-power LEDs are normally driven with a special constant-current power supply.   As with small LEDs and a resistor, with the proper current the voltage "falls into place".      You can use a regular constant-voltage power supply and a power resistor, but the resistor needs to dissipate (waste) about the same amount of power as the LED (depending on the design details) so this is a poor design and it's rarely done.      There are dimmable/controllable constant-current LED power supplies/drivers.    (Technically, the dimmable supplies are controlled  current.)    



I have linked the products above.

I was following this tutorial https://www.instructables.com/id/Sound-Reactive-LED-strip/

So I could power the DC booster from a seperate 5v usb cable and use the mosfet or switch built into the arduino to control the "blinking" ? So to do this I would plug the -Vin on the booster into the arduino for control?

Thanks for the help.


Jan 15, 2019, 05:37 pm Last Edit: Jan 15, 2019, 05:40 pm by wolframore
This is the best I could find... there are many similar chips being made in China... and forward current is 1000mA

Bad Boys Race Our Young Girls But Violet Generally Wins - Get Some Now :) - ELI ICE man


You should use a constant current drive for LEDs like this, otherwise it could undergo thermal runaway.
Yes it happens to work at 10.5V, but if you monitor the brightness with a photometer and the current
through you may see that the current and brightness drifts up as it heats up - its not stable.

A series resistor can be used to limit current as an inferior way of driving this, but a constant current
DC-DC converter is how to do it properly and with max efficiency.
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