PCA9685 Signal Voltage to low dimming LED-Stripe

Hello,

I'm building my first Arduino project. So all this stuff is quite new to me ;). I want to dim a LED stripe using a Mosfet Module. If I'm connecting the Mosfet Module directly to my Arduino Nano everything is working fine.
But I want to control some more LED stripes. So I'm using a PCA9685. My Problem is that my Signal Voltage is going down, when I'm connecting my Mosfet Module with the PCA9685. The signal without the Mosfet Module is 5V but after connecting it with the Mosfet the Voltage is going down to around 3.7V and the stripe is not reaching it's maximum brightness.
Connecting the Module directly with the Nano is no problem and the Voltage is stable at around 5V.
Has someone an idea why this is the case and how I can fix it? The amperage from Nano is around 80mA and from the PCA only 20mA. Is this the reason?

I would appreciate a small hint. Even after some long search I couldn't find a solution.

Thank you and best regards

Marcel

In your sketch I don't see a ground from the IRF540 module to the arduino ground. Is this the case in your circuit?

The ground is connected. But I don't think that it matter. It is working perfectly only with the sig-port connected to the arduino. The only thing that is bothering me is the voltage drop with the PCA9685.

Here is a sketch of PCA9685 version:

Screenshot 2019-09-28 at 19.19.14.png698×618 109 KB

Screenshot 2019-09-28 at 19.19.14.png698×618 109 KB

PCA9685 modules have a 220 ohm resistor in series with the output.
The real problem is that mosfet module.
Wrong mosfet and wrong circuit.
Leo..

If that's an IRF520 (image says IFR520, which is probably a typo as there's no such MOSFET) it won't switch on properly at 5V to the gate.

You need a logic level MOSFET.

MarcelBreska:
he amperage from Nano is around 80mA and from the PCA only 20mA. Is this the reason?

That also can't be right as a Nano can not source or sink more than 40 mA on a single pin, and a MOSFET's gate does not require current, just voltage.

Thanks for the replies! The Mosfat is an IRF520. What Mosfet would you recommend for dimming an LED-stripe?
It is working quite fine, but I'm not getting the maximum brightness. Has anyone an idea why the voltage is dropping after connecting the PCA9685 with the Mosfet? When I'm measuring the PWM-Pin-Voltage of the PCA it is around 5V and after connecting it with the Mosfet it is dropping to 3.6V.
If I measure output Voltage of D7 for example it is 5V and it stays around 5V even if I connect the Mosfet. I'm happy with the brightness in that case.

The IRF520 is never going to open properly even with 5V at the gate. It needs 10V or more. You probably don't have much of a strip, drawing <1A or so of current.

Get a logic level MOSFET. IRL520, IRL540, IRLZ44N are just a few examples that come in easy to solder TO220 package. Those will work a lot better already

MarcelBreska:
It is working quite fine, but I'm not getting the maximum brightness. Has anyone an idea why the voltage is dropping after connecting the PCA9685 with the Mosfet?

The indicator LED on that mosfet board reduces gate drive voltage when connected through the 220 ohm resistor on the PCA9685 board. An Arduino pin doesn't have that series resistor, so produces a higher drive voltage.
Can remove/desolder that indicator LED, but an IRF520 mosfet is never going to work properly with an Arduino.
Leo..

Up to 1 amp or so the IRF520 will work fine on 5V Vgs but beyond (and face it, with a LED strip that's pretty easy) it's a terrible switch. As for a mosfet I keep IRLB3034 (TH) and IRF7013 (SMD) on hand

And on the PCA9685, no idea which library you use to drive it and how it configures the chip, in order to drive something on the output HIGH, the 'OUTDRV'-bit of the output needs to be set.