I'm trying to use an Arduino Uno to control a 12V signal using an N-channel MOSFET. After doing some research, I decided on the TN0702 and ordered a couple in case of problems. I supplied my MOSFET with 5V at the gate, connected the drain to my 12V high and the source to ground. I also added a resistor behind the gate.
My first couple of tests, everything worked exactly as expected and the MOSFET hardly even got warm. Around the 5th time I used it, however, the signal was passing through even without supplying voltage at the gate. I pulled the transistor out and confirmed with a multimeter that the source and drain had shorted.
This is pretty much my first experience with using transistors and ordering parts, so I'm not very experienced with reading datasheets. I noticed that the "Maximum Gate Threshold Voltage" was marked as 1V, but I'd assumed it meant that anything over 1V guaranteed the gate to open, and not that the transistor could breakdown past 1V. Was that assumption wrong to make?
For context, the 12V signal is used to power a relay. Ideally, I could find a relay with a 5V threshold and drop the need for a MOSFET, but in my case, this relay is built into a circuit board that I'm not supposed to alter. Essentially, my project is to use an Arduino to breathe life back into an old load frame controller from the 1990s without really messing with the internals. It used to be controlled with a physical control panel, but my boss wants to wirelessly control it with his computer via the Arduino.
Yeah... I'd guess you forgot the diode and the [u]Back-EMF[/u] from the relay coil fried the MOSFET.
Or if you didn't forget the diode, yes it could be [u]ESD[/u] when you touched the circuitry. (You don't have to see or feel a spark to get ESD damage.)
For context, the 12V signal is used to power a relay. Ideally, I could find a relay with a 5V threshold and drop the need for a MOSFET,
Most electro-mechanical relay coils require more current than the Arduino can supply so even with a 5V coil, you generally need a driver circuit.
There are solid state relays that can be directly driven by the Arduino and they're non-inductive so you don't need the diode, but you have to be a little more "careful" on the output side. (For example, AC & DC solid state relays are generally not interchangeable.)
KimchiBean:
I pulled the transistor out and confirmed with a multimeter that the source and drain had shorted.
That's not telling you anything if the gate is left unconnected. MOSFETs should never be left with a floating gate as the gate is effectively a capacitor and can hold a charge for long periods, or be constantly trickle-charged through small leakage currents.
Short gate to source, then measure the resistance between drain and source.
Set the gate to +5V w.r.t. source and measure it again.