Hi everyone!

Sorry for the silly question about my problem. Unfortunately I couldn't find a proper solution.

Here is my basic circuit. My led is metal button's led which works with 12-24V.
When i turn mosfet on with logic high from arduino, everything works fine. I read 24v from Vled with multimeter.
But when i turn mosfet off with logic low from arduino, (here is my problem) led flickers slightly. I read 2.4v from Vled with multimeter.
I tried 2 mosfets IRLML0030TRPBF and PJA3440. I had same results. I tried 1k, 10k and 100k on R1, 470ohm and 1k on R2. It changes Vgs between 3.8v-4.5v.

How can i solve this problem?

Best Regards

 

Hi everyone!

Sorry for the silly question about my problem. Unfortunately I couldn't find a proper solution.
View attachment 292988
Here is my basic circuit. My led is metal button's led which works with 12-24V.
When i turn mosfet on with logic high from arduino, everything works fine. I read 24v from Vled with multimeter.
But when i turn mosfet off with logic low from arduino, (here is my problem) led flickers slightly. I read 2.4v from Vled with multimeter.
I tried 2 mosfets IRLML0030TRPBF and PJA3440. I had same results. I tried 1k, 10k and 100k on R1, 470ohm and 1k on R2. It changes Vgs between 3.8v-4.5v.

How can i solve this problem?

Best Regards

You need a small value resistor (try 22K) in parallel with the LED to ensure that the voltage pulls up to 24V when the MOSFET turns off to shunt any leakage current. If it still glows, try a smaller value, e.g. 10K, until it no longer does.

 

Try shorting the G-S of the MOSFET at the transistor just to prove it is off.
There might be grounding problems. Where there is voltage see by the gate but our meter measuring at the computer does not see it.

 

You need a small value resistor (try 22K) in parallel with the LED to ensure that the voltage pulls up to 24V when the MOSFET turns off to shunt any leakage current. If it still glows, try a smaller value, e.g. 10K, until it no longer does.

That’s nonsense. The leakage current is specified at <1uA and that would not illuminate the LED.
Either your LED or your MOSFET is dead because there is no current limiting resistor in series with the LED.
Is your Arduino 0V connected to the MOSFET source?

 

Two MOSFETs all need Rds(ON)=4.5V, so you can set R2=100 ohm or short.

If you do that but still can't solve the problem then you can try to use two stages of NPN, PNP(connected to 24V) transistors and NMOSFET.

Or using photocoupler pc817 and NMOSFET.

 

The buttons in your link don't seem to have any LEDs ??
What is the LED spec? If the LED doesn't have a series resistor then applying 12-24V to it will destroy the LED and possibly the MOSFET.

 

I think the TS mentioned his LED was in the switch, maybe the link is not to the correct illuminated version.

 

" It changes Vgs between 3.8v-4.5v. "

Sounds to me like your micro is not pulling to ground.

 

That’s nonsense. The leakage current is specified at <1uA and that would not illuminate the LED.
Either your LED or your MOSFET is dead because there is no current limiting resistor in series with the LED.
Is your Arduino 0V connected to the MOSFET source?

Hi there,

Some high brightness LEDs can glow at very low current like 10ua.
But i have to agree this looks strange that there is no resistor in series with the LED. I would bet that the LED blows out, but maybe the MOSFET does too or something.
Some LEDs that get a current too high start to flicker rather than burn out completely right away.

 

Measuring the voltage across an LED when a transistor is "off" can give strange readings because when a LED is not conducting the resistance can be somewhere close to the transistor's resistance.

But that Vgs is the real clue.

 

Measuring the voltage across an LED when a transistor is "off" can give strange readings because when a LED is not conducting the resistance can be somewhere close to the transistor's resistance.

But that Vgs is the real clue.

Hi,

I assumed he was talking about the 'on' voltage level only (or 'off' only), but yes you may be right with your assumption.

 

As noted by others, check why your gate voltage isn't what you expect. Shorting R1 will confirm that the LED goes off as expected, and that simple test eliminates the need to diagnose anything to the right of R1 in your diagram.