MOSFET for switching LEDs dimming

Hello guys,

I have been struggling with this project for quite some time.

Pretext: I want to be able to recreate "dynamic" blinker lights on my car.

How I realize this:
A couple of buck converters (Constant current)
Mosfets for switching.

After two weeks of use, the leds start to dim after each turn signal cycle.

Video of the Problem:

First, I used these Mosfets: PHT4NQ10T
I tried replacing them with these: IRLIZ 44N

For the first two weeks after replacing the mosfets, it works fine.. after that, it start dimming one after another...
Fun fact: The rear lights are operated with regular bipolar transistors and work SUPERB :slight_smile:

If you need more information, I will gladly provide it.

Thank you very much :frowning:

Both listed mosfets are non-logic mosfets, and are not really suitable to be driven by 5volt logic.
You need "logic level" mosfets.

Is the dimming caused by the mosfets?
Don't know untill you post a full diagram and a link to the LEDs used.

The IRL1Z44N is logic level.

I suspect you've blown the gate oxide or something - the automotive environment is harsh - I'd
suggest using a 6.8V zener directly across gate and source on every MOSFET to protect the
gate oxide from voltage spikes. The leads driving the gates should be short and low inductance if

A photo of the driver board would be instructive...

The IRL1Z44N is logic level.

Yes, must have looked at the IRFZ44 datasheet.

Have you checked how hot your FETs get? You don't specify how much current the LEDs draw.

Welcome to the forum.

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

Thanks... Tom... :slight_smile:

Hello, a quick answer to a couple of questions:

Current draw is 1 Amp.
The Fets don't even get warm.

Will post a circuit as soon as I can, definitely!

I thought the DC-DC switch mode PSUs would filter out all the harshness of car environment...

"Is the dimming caused by the mosfets?" When I replace the Mosfets, everything works fine for about 4 weeks, so I'm pretty sure that's the cause.

Thank you all for helping so far :slight_smile:

Try a different MOSFET then, such as AOI514 or AOI510 from digikey

Are you using PWM on mosfet or just swicth on/off?

Ciao, Ale.

Hello, thanks again for the replies and I apologize for not being able to write anything, I've been very swamped with work lately.

I had the time to draw a little sketch in circuit of what is basically running in the car.

Instead of the 100Ohm Resistors on the LEDs I am using DC-DC Constant current buck converters set to 1 Amp.

Everything else is basically the same, it's a very simple circuit so I don't know where the problem is coming from:

ilguargua: I am using just Switch off / on Logic Level with the 5V Arduino pins.
CrossRoads: Thank you for the suggestion, I switched Mosfets 3 times already, after about 2 weeks of running they start dimming, what makes the one you suggested better?

Thank you :slight_smile:

OPs circuit;

Tom... :slight_smile:

Have you got the gnd of the 12V Supply cannected to the gnd of the arduino?

Tom... :slight_smile:

Since you need just to switch on/off, I'd use a better suited part, like a BTS432e2, or similar. They are designed for automotive use, including protection for shorts, over heating, etc. A bit more expensive, but will save you a lot of trouble. The part indicated is just an example, and is quite old, search for "automotive smart high side switch" for newer parts. Ah, and the part is an high side switch, so is switching positive, just adapt your schematic.

Ciao, Ale.

Have you got the gnd of the 12V Supply cannected to the gnd of the arduino?

Tom... :slight_smile:

Hi, everything is connected to car batt ground. +12V from the batt and the Arduino is powered via Buck converter to 5V to car ground.

@ ilguargua: I will take a look at them, wouldn't it also be possible to use regular PNP bipolar transistors? Or are they not suited because of the high amperage?

Yes, I guess you can also use PNP transistor, or p channel mosfet. The point is , as you have already experienced, automotive environment require some sort of protection for the parts involved, so if you take care of that you can use whatever you want. The part that I suggested is designed for working in such environment, and has almost of protection already included.

Ciao, Ale