Using DirectFET from IRF for DIY amplifiers

TO-220 vs. DirectFETThe new series of FETs from International Rectifier called DirectFet, are not really DIY friendly :roll:

Look at the comparison between a normal TO-220 stle of MosFet, here IRF640 that I have used in my 400W amp. Besides is the tiny IRF6785 DirectFET which should we good for the same kind of amp size!!!

These MosFets are surface mounted devices with a “ball grid array” of 3 points at the bottom, for Gate and Source.

The top is a metal shield that is also acting as the Drain conductor.

How do you use therse for DIY? And why should you?

Well for a Class-D amplifier these divices have many advantages. Very litle lead induction, as there are no leads. They are very small which can result in a very compact layout, which will lower the EMI noise it will be emitting when switching.

But how do you solder these?

Well I just bought two samples, to have a closer look. They are indeed very small …. tiny I would say.

I have been thinking about using some larger vias (1mm hole) positioned right under the balls for D and G.

Then you should be able to solder from the other side. Maybe you need to put a thin layer os solder on the top side before putting the fet on, and starting to sloder from the other side ……

Have anyone out ther tried something like this and has som experience??

IR6785 top side

Here is the DirectFET (IRF6785) seen from the top. As can be seen from the paper it is placed upon, it’s only some 5 x 5 mm in size!

As for heatsink you can just use a small one with some double adhesive thermal conducting tape between. But as they are this small a heat sink will be needed, even tor test purpose. With class-d using TO-220 devices, I normaly don’t put on a heat sink when running the prototype on a low voltage (2x15V)

 IRF6785 Bottom view

Here is the DirectFET seen fom below. Look at the small contact points! …… can this be used for DIY?? ……. it has to be tried out :)

7 comments to Using DirectFET from IRF for DIY amplifiers

  • Greatings, Thank you! I would now go on this blog every day!
    Thank you

  • admin

    Thanks to you for the kind words :)
    Happy thate someone finds it interesting :)

  • I am definitely bookmarking this page and sharing it with my friends.


  • I somehow dont agree with a few things, but its great anyways.

  • mjp

    I know this post is a bit old, but any luck soldering this guy? Or finding a replacement?


  • admin

    No I newer got further with this. Actually I dont really think these devices will take up less space in practice, than TO220 devices, as you need to mount a heatsink on the PCB. But there are some advantages with less parsitic with these devices.

  • Jezza

    no, you dont NEED a board mount heatsink (which can be very low profile anyway) they are designed to use the PCB copper as heatsink and these things have such high gM and low gate resistance, low gate and output charge, that they may not even need to dissipate so much in audio. You use the PCB primarily and top mounted heatsink to augment it if needed and thus dissipate from both sides, they take up much less space, its not even close

    I think they are very interesting and have just bought some to try in both class A and D type designs, the D will be direct USB->DSD->Class D. using them properly of course assumes proper PCB layout and a hotair rework station or reflow oven (I have a small toaster oven type with controller) and a cheap ebay hotair tool.

    if you wish to use any of the newer high performance parts, you will need to learn to use these new layouts and tools; more and more parts do not have leads now and performance is always better because of it

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