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:
- 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!