oops ... pop :( learning about MOSFETs

In books, the descriptions of MOSFETs are so simple; look at a MOSFET data sheet and it isn't quite so simple. The most big question in my mind is the drain current min - why is there a min. Does that mean that the MOSFET can support at least that specific current?

The IRF531 looked nice, so I bought a couple to learn with. I'm have a pretty basic multimeter and a limited set of resistors, so I bread-boarded some circuits with the intent of getting a most basic understanding. Here are my notes in preparation for bread-boarding and testing:

Specific Constraints
- 0-25 mA and 0-250 mA test ranges on multimeter
- 330 ohm and 470 ohm resistors are only small resistors available
- both types of small resistors are 1/2 watt resistors

Playing with MOSFET
- assuming no resistance at all on gate-source
  - circuit: +5 ... 235ohm ... gate-source ... Gnd
  - 21 mA used
  - if resistance on gate-source, then current used will be smaller
- assuming negligable resistance (< 1ohm) on drain-source
  - circuit: +12 ... 660ohm ... drain-source ... Gnd
  - 18 mA used
  - if 5V @ 20 mA isn't enough to turn MOSFET on, then current will be smaller

You know what's coming - after careful consideration of my constraints and building my circuit, I blew the fuse in my multimeter! I have no spares, so I'll have to finish testing tomorrow :( My mistake, besides doing this in real life rather than with Crocodile Clips, was that I didn't plan my volt versus amp metering locations. Live and learn - at least I lived...



Now that is the smart way to learn! The 3D view is pretty and neato, but what I'm not showing is the schematic with ammeter and voltmeters installed. Good stuff!