What do they do?

[Electronics4you]

I found this MOSFET circuit **broken link removed**, and I would really like someone to explain what the two capacitors do. And why are there two in parallel with two where different values. In another MOSFET circuit I'm doing I use 1nF grounded capacitors on each gate - but what are they exactly doing?

 

[Nigel Goodwin]

They are supply decouplers, the 470uF decouples at low frequencies, and the 0.1uF decouples at higher frequencies (where the electrolytic won't work well).

 

[Hero999]

Are the diode really required?

I never bothered with them since they're built into the MOSFET and I know that they're slo but most MOSFETs can safely dissipate a small amount of avalanche energy.

 

[Nigel Goodwin]

Are the diode really required?

Depends if you want a reliable project or not?, the external diodes cost very little but provide a great deal more protection than the internal 'diodes', which are probably only a byproduct of the manufacturing process anyway, and not intended for such use.