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Q&A

Comments on MOSFET not turning completely off

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MOSFET not turning completely off

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Hello everyone,

I have a simple circuit in which I control some LEDs via an MCU and DMG2302UK ( N-channel MOSFET )

Circuit schematic

The EN pin is connected to an MCU gpio pin that works at 3.3V.

The circuit worked perfectly for some time, and suddenly the LED were always-on (very dim), there was some sort of leakage current, changing the resistor and the capacitor didn't help, it only worked again when the MOSFET was changed with a new one.

Note that the MOSFET was switching successfully as I can see the LEDs turning brighter when switched ON, but it just doesn't turn completely OFF

I imagine that something might have damaged the MOSFET but not sure what, the main thing I am thinking about is not connecting a resistor between the gate and the EN pin which might have damaged the MOSFET with time as per this page

What do you think might have damaged the MOSFET ? and how to enhance this circuit ?

Thank you

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1 comment thread

LED current limiter? (2 comments)
LED current limiter?
Lundin‭ wrote about 3 years ago · edited about 3 years ago

How do you limit the current of the LEDs? Right know you are feeding them with as much as your power source can give. What makes you think it's the MOSFET that's blown? It is far more rugged than the LEDs, rated at several A, while the average LED is rated at 20mA.

AhmedMobarez‭ wrote about 3 years ago

The LEDs operate between 400-700mA, there are 10 LEDs in two parallel branches, and there are current limiting resistors. as the LEDs were never damaged I excluded their details from the question. changing the MOSFET returned the circuit to normal operation