Problem to reach full brightness with an UV led and PWM

Other Hardware LEDs and Multiplexing
1

Hi everyone, let me know if this is not the right place to post this.

I have come across a very weird problem : I want to control an UV led (https://www.amazon.fr/dp/B0BD492VPT?ref=ppx_yo2ov_dt_b_product_details&th=1) with PWM but can't reach full brightness.

Let me explain :

When I connect my led to 5V and GND, its brightness is at its maximum level.
But with the PWM, at 100% : analogWrite(ledPin,255) I can only get around 50% of the max brightness.

The code is very straight forward for now, I just want my PWM to be able to reach the same brightness level of my 5V (see below).
Same for the electronic, I'm just plugging my anode to a digital pin with PWM, and my cathode on the ground.

When I do it with a classic led (non-UV) it works fine.
I've tried with different Arduino Uno brand (The official Rev4 one, and a few other brands with Rev3).
I've tried with all my PWM digital pins, and also tried different PWM parameters (changing the frequencies, the PWM modes, etc).
I've tried with the Arduino plugged to the computer, as well as different external power supplies.

One of the things I don't really understand is that this led is announced with 5W and a 5V-1A power supply, even though it seems to be working fine when plugged to the computer USB (5V but not 1A at all If I'm right).

Let me know if I have to change this post of if you need anything more


int ledPin = 9;

void setup() {

 Serial.begin(115200);
 pinMode(ledPin,OUTPUT);

analogWrite(ledPin, 255);
}


void loop(){}

Thanks a lot for your help !

2

You cannot power a 5W LED directly from an Arduino pin.

You should limit the current from an Arduino Uno R3 to 20mA. See the specifications at https://store.arduino.cc/products/arduino-uno-rev3.

For an Arduino Uno R4 , the limit is even less, at 8mA.
https://store.arduino.cc/products/uno-r4-minima

You need to use a transistor or preferably a MOSFET to switch the 1A that the LED requires.

Generally a resistor is needed in series with the LED to limit the current to a safe maximum, but as the LED that you posted the link to already operates from 5V that is not necessary.

3

Thanks John.

I changed my plan thanks to your answer.