Transistor makes LED strip dimmer?

Using Arduino LEDs and Multiplexing
1

I’m using ESP32 to control the brightness of the LED strip. The LED strip is 12V, white color.
I connected the LED on a separate board with an isolator between this board and the ESP32 board. This board is supplied with 9V.

The problem is, I’m using IRF520, and connected pin1 to ESP32 pin from the isolator, pin2 to ground of the LED, and pin3 to ground. The power of the LED is connected to power (9V) on that board. However, this turns out very dim even if i didn’t use a resistor and just did digitalWrite HIGH.
If i connect the LED straight into power and ground on the board, its much brighter. Why is this? And how can i fix this?

2

Even a logic-level FET would struggle at 3.3V.
Do you have logic-level FET?

3

I see. I looked at this post arduino - Difference between IRF520 and IRLZ44N? - Electrical Engineering Stack Exchange
Do u think switching to irlz44n would solve my probelm? Thanks!

4

Hi @aj592

The IRF520 has a VGS of 4V, so the transistor won't fully turn on till the gate has 4V.

The IRLZ44N has a VGS of 4V also, so that one won't work either.

I usually use the STP90NF03L. It has a VGS of 2.4V.

5

Wrong. The IRF520 has a VGS(th) which may be as low as 2.0 V, or may be as high as 4.0 V, meaning it may not turn on at all below 4 V and will generally not conduct well at 5 V.

It is indeed, quite unsuitable.

Quite wrong again. The IRLZ44N is specified as a logic-level FET with a maximum VGS(th) of 2.0 V. Its RDS(on) at 4.0 V is specified as no more than 39 mΩ.

It should be quite suitable up to several Amps if you examine the characteristics.

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