mA increase - MOSFET FU9024

[cyberctrl]

View attachment Network Time Circuit.pdf

Could you please advise where is the mistake in my attached schematic. My mosfet is the FU9024. I am trying to control a power LED of 3.3V 700mA from a source of 3.3V 10mA powering with external source of 12V-1.5A
thanks for any answer

 

[alexan_e]

You are using a Pmosfet and you have it reversed, you should connect the source to the +12v and the drain through the resistor to the led and then the other side of the led to the gnd.
You will also not be able to control the mosfet with 0-3v3 because the mosfet will be always on, any voltage below 9-10v to the gate will turn the mosget on.
You can use a trnsistor if you want to translate the 0-3v3 to 0-12v so that you can control the mosfet.

Alex

 

[cyberctrl]

thanks a lot for the answer!
very helpful..I wrongly wrote though on the schematic PC017.It is the PC817-sharp.Is this not capable of switching on/off the MOSFET?

 

[alexan_e]

Yes PC817 can drive your mosfet

Alex

 

[cyberctrl]

Hello and many thanks for the answer. I am sending you an image with Drain and Source corrected. I guess, I am doing something wrong from the BC817 to the FU9024.Can you identify something wrong in the image?

 

[alexan_e]

You haven't used a resistor to limit the current of the optocoupler diode, it says 1.4v 20mA so you should use (3.3v-1.4v)/0.02A=95 ohm
A resistor about 100-150 ohm would be fine, unfortunately the diode is probably damaged already from the over current.
Do you have a multimeter to check the forward voltage of the diode?

Alex

 

[cyberctrl]

That was it!!!I gave it too much current and I destroyed the optocoupler!!I replaced it and it works fine now!!!million thanks!!!