Alright, so today I wanna talk about figuring out those MOSFET current calculations. Man, I remember when I first looked at those formulas – total nightmare! Big scary equations with Greek letters everywhere. Made my head spin.
The Spark Moment
Started when I was fixing this busted power supply last Thursday. Needed to replace the MOSFET but couldn’t find specs anywhere. Grabbed my multimeter but kept getting nonsense readings. Realized I’d have to actually calculate the damn current myself.
First Try Disaster
Opened up three different textbooks – big mistake. Each one showed different versions of the formula! Decided to try the “simplest” looking one:
- Plugged in numbers like crazy
- Got negative current values (how?)
- Spilled coffee on my notebook
- Cursed at my calculator
That’s when I remembered what Mr. Wilson said back in trade school: “If you can’t explain it in dirt with a stick, you don’t understand it.”
Dumbed It Down
Cleared everything off the garage floor. Grabbed my kid’s sidewalk chalk and drew:
- A big rectangle for the MOSFET
- Arrows showing current flow
- Three key numbers: gate voltage, threshold voltage, transconductance
Started connecting the dots physically. Realized it’s just like water pressure through a valve – except with electrons instead of H2O.
The Lightbulb Click
Finally got it when I made this stupid analogy:
- Gate voltage = how hard you turn the faucet
- Threshold voltage = minimum pressure before flow starts
- Transconductance = pipe thickness
The actual formula becomes stupid obvious: (how hard you turn minus the minimum) multiplied by pipe thickness. That’s literally it.
Workshop Testing
Tried this on five different MOSFETs yesterday:
- Wrote the chalk formula on my workbench
- Took measurements with actual probes
- Dumbed down method matched real-world results every time
- Got excited and welded the chalk to my bench accidentally
Realized all those textbook variations just overcomplicate the core idea. Once you get the faucet/pipe picture, you can reconstruct any version. Still got chalk dust in my hair, but at least I ain’t scared of those equations no more.