PQFN 5X6mm Packaged N channel Power Mosfet in ClassD ...

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#22
You can use some aluminium oxide pads under the QFN thermal
pads on the back side of the PCB to provide the isolation.
The main heatsink will be thermally connected to the PCB trough these
aluminium oxide discs with very small thermal resistance.
Of course you need to make your custom heatsink and think about
a method of fixing it to the pcb.
 
#25
To Workhorse ...

Can I use you're class D design to put PQFN IRFH2050 and see how it works?
I am asking because I need a class d functional design to just modify a bit.
Hope you will help with design.

Best regards,

Savu Silviu
 
#28
Hi Workhorse...

Any solutions on how to avoid problems generated by this body diode?

I'm new in all this so any guidence will be very valuble to me.

Thanks for the tip. I went past the curent rating of the body diode.

Best regards,

Savu Silviu
 
#30
IRFH5015 is only rated at 150V
but it has body diode 56A.

Around witch value is a body diode of a transisstor used in a class d condidered fast?
Trr of IRFH5015 si 2 times smaller than the famous IRFB4227

Regards,

Savu Silviu
 
#34
Hi Marc,

I was thinking these days...
Since a lot of people have done this amp: http://www.diyaudio.com/forums/class-d/166214-ucd-25-watts-1200-watts-using-2-mosfets.html
Why not make this one using SMD parts and also using the IRFH5015 mosfet.
I think it will become a very small amp with very low part count and if cooled properly a powerful one.
Now since IRFH5015 is rated at 150Vdc I am thinking of using power supply rated at +/- 70Vdc.
Attached is the schematic with parts rated for +/-70Vdc use.

For modification I presume that RF1 and RF2 would be rated at 10 Ohm, DE1 would be MURS120, all the 2N5401 would be replaced by BF821, RD1 and RC1 would be left trough hole type for better temperature dissipation, QF1 and QF2 would be IRFH5015, LG1 would be wound on T106-2 Micrometals Iron Powder Core.

This is all I can propose for the moment.

If anyone has any useful input on this matter they are free to express themselves since I think of this attempt as a way of bringing SMD components and SMD solder techniques to the enthusiastic DIYer.

Best Regards,

Savu Silviu
 

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#35
Hi,
that does look like an interesting project, and with SMD would be quite small.😀
Cooling will be interesting, but I have an IDF interface to SolidWorks so can create a SW model for your friend to play with. I have worked on products before where the case is also the heatsink.
I'll print out the schematic tommorow and collate all the parts into my CS library.
The power dissipation of the resistors will be rquires and also what size of case to go down to for the smaller devices. For a first pass, especially if there is going to be manual building 1206's would probably be best. Though depending on power disipation etc it will be fun to do a version using the smallest possible devices, just to see how small it can be made.
As I said I'll get the parts done tomorrow and aim to start layout over the weekend.
Soon
Marc
 
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