Okay so I ran into this issue yesterday where my MOSFET just wasn’t performing right. The transconductance was way too low, man. Like I’m testing this thing and thinking “why’s this circuit acting so weak?” It’s supposed to handle more current but it’s choking big time.
First step: hooking up the gear
Grabbed my multimeter and scope, hooked everything up cold. Power supply set to 15V, load resistor looking like grandma’s old toaster coil. Fired it up and bam – readings are all wrong. Drain current’s barely crawling when I crank the gate voltage.
What I checked
- Double-checked connections – yep, everything’s plugged right
- Tried different power levels – same junk results
- Swapped MOSFETs – new one’s doing the exact same garbage
Started sweating a bit cause this project was due last week. But took a deep breath and said “let’s methodical this thing”.
Making some adjustments
First move: Upped the gate voltage way higher than spec. Didn’t fry it but still no improvement. Transconductance measurement came out at like 0.5 S when it should be around 2 S for this setup.
Second try: Changed out the pull-down resistor at the gate. Went through all my bin resistors like a crazy person. 10K? Nada. 1K? Still junk. 100 ohms? Now we’re talking little better but still pathetic.
Lightbulb moment: Realized I forgot the gate protection diode when I rebuilt this board last month. Slapped that in there and – boom! Gate voltage stabilized instantly.
The magic fix
Finally tried putting a small capacitor between gate and ground. Used this ceramic 10nF cap I had lying around. Powered it up and… sweet fancy Moses! Drain current jumps up like it’s Christmas morning. Meter shows transconductance at 1.9 S – close enough to call it fixed!
Took me three coffee refills and two busted prototypes, but she’s running smooth now. Moral of the story? Always triple-check your gate protection. That thing’ll bite you every time.