MoSFeTz

decoding the IR-series mosfet numbers: (based on info at [fairchild])

prefix IR gate level

 L (logic level)
 F (higher level)

packaging (default to-220)

 5xx 6xx 7xx 8xx
  w - to-263
  s - to-220f
  i - to-262 
  nl - to-92l
 1xx 2xx 3xx 4xx
  m - sot-223
  p - to-3p
  r - to-252
  s - to-3pf
  u - to-251

first digit is voltage:

 1xx - 100V       5xx - 100V
 2xx - 200V       6xx - 200V
 3xx - 400V       7xx - 400V
 4xx - 500V       8xx - 500V

second digit is wattage (goes up, but not the same across lines)

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A suitable mosfet for direct connection to PIC/AVR is the IRL510. In general, you need a logic-level mosfet to interface directly to a micro.