Class D using PQFN 5X6 mm MosFets

In my quest for making an all SMD Class D amp (see other post) I found that you can get some really good new Fets in very small PQFN 5x6mm packages. Some even come with a dual cooling option where you have a cooling pad on top as well as on the bottom. Gives a lot of opportunities.

I decided to try out some of these fets, namely the FDMS86200DC from Onsemi, which is a super fast 150 V, 35 A, 18 mOhm fet. As it is only 150V the power in 8 ohm will be limited, but still using +-60V will give a max power of ca 200W in 8 ohm. But lets see how it all works out.

The PCBs were received today from JLCPCB, and this time it was really fast only 12 days after I placed the order, and this with the normal low-cost mail option.

As can be seen, I have chosen to only get the components mounted which are classified as “basic” components by JLCPCB, as the “extended” parts cost an extra 3 USD for each type. So there is a bit of soldering to do.

I’ll have some challenges with the FETs though. As I have made all efforts to use the PCB as a heatsink, it will be super difficult to heat up the pads with a small soldering iron!
I have just ordered a small pre-heating plate, but that will not arrive before May.
Will try to preheat it with a hot air iron.

Stay tuned for the results 😉

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