MOSFET heating on my amp...

thefish

Member
2006-10-28 7:38 pm
I finished the second revision of my class D amplifier (schematic) but there is a lot of MOSFET heating. If I remove the 0.1uF caps from the power supply there is less heating but more overshoot.

[IMGDEAD]http://www.siliconlite.com/images/AMP/Board-A.jpg[/IMGDEAD]

High and Low side gate signals with power supply caps:
[IMGDEAD]http://www.siliconlite.com/images/AMP/gates_w_cap.jpg[/IMGDEAD]

High and Low side gate signals without power supply caps:
[IMGDEAD]http://www.siliconlite.com/images/AMP/gates_wo_cap.jpg[/IMGDEAD]

There is also a good deal of hissing when the input is muted (this was not in revision 1).
 

thefish

Member
2006-10-28 7:38 pm
Anyone have any ideas why this would be happening? Should I use a larger cap on the power supply (maybe 1uF) connection to the FET's? I put a FM radio right next to the amp (withen 6 inches) and get no interference. When I actually rest the FM radio on top of the amp it interfears a lot (even makes the digital dial jump around??).

When the power supply caps are removed it seems that just one of the low side mosfets gets hot fast, the rest are ok.
 

thefish

Member
2006-10-28 7:38 pm
I swapped the 0.1uF caps with 1uF caps and the traces look much nicer now but it still had the heating.

[IMGDEAD]http://www.siliconlite.com/images/AMP/gates_w1uF_cap.jpg[/IMGDEAD]

Searching through my resistors I dont have any smaller ones for the gate :bawling: I am thinking maybe 10ohm should do it.
 

thefish

Member
2006-10-28 7:38 pm
Well I have let it run for 6 hours with a 19V supply at 6 ohms and it is cool (only the inductors are a bit warm). It sounds nice as a sub amp, for mids and highs it is ok, no real hissing. Does not seem to cause any FM interference unless radio is within 2 inches (and parallel to the doughnut face) of the inductors. The output is not very nice looking on the scope 2V p-p noise on the signal.


Scope image at 5V/div with a 100hz test signal input into amp:
[IMGDEAD]http://www.siliconlite.com/images/AMP/Output_5V-Div.jpg[/IMGDEAD]

I think changing the output inductors should clean this up. Thanks for the help everyone.