mosfets and class d amps

[Tekko]

Which MOSFETS would be good for class d amps ?

IRF640 has alittle high Rds(on) i think. Would these below work ?

STP24NF10
STP40NF10
STP80NE06-10

Less Rds(on) should give less heat and allow higher voltage for more power, no ?

[Tekko]

Wow only 8 views in a whole day So NOBODY here knows then ?

[gmikol]

Low Rds and low gate charge are 2 of the primary factors to consider. The third is VDSmax...Maximum drain to source voltage. The devices you mention are only 100V parts. A good rule of thumb is to use parts rated for Vcc + Vee + some safety factor to handle the inductive output load. So 100V parts should maybe only used with +/-33V rails. You might be able to push it a little higher, but you'll have to check what the reverse recovery spikes look like with a scope to make sure you're still saft.

If that works for you, then you'll have to look at balancing power losses from Rds in the output stage (twice as large for the STP40 device) vs. power losses and heating in your gate driver due to the much larger Qg of the STP80 device vs. the STP40 device. Keeping in mind that the gate driver is not typically mounted to a very robust heatsink compared to the output devices.

I hope this helps you out a little bit.

--Greg

[MOER]

We have done a lot of research. The best Mosfets for Class D are those which have low gate charge, however if you are using either a driven or self oscillating type, higher Qg types will work as long as you pay attention to dead time.

IRFB4212 100v 0.058R 15nc
IRFB4019 150v 0.08R 13nc
IRFB4020 200v 0.08R 21nc
IRFB23N15D 150v 0.09R 37nc
IRF540N 100v 0.044R 71nc

FDP39N20 200v 0.066R 38nc
FDP42AN15A0 150v 0.042R 33nc
FDP3682 100v 0.036R 18nc
FDP3652 100v 0.016R 41nc

I have tried all the above. The IRF540N is the least expensive and the Fairchild FDP3652 the most. I can obtain low THD numbers with any of tghe FETS, bit of course the lower the gate charge the lower the deadtime and the coller the FETs run.

RDs on is not a huge thing as typically you are not driving the FET to its current limits.

[Tekko]

I want to have rails that goes up to 65-70 volts so i can reuse a nice large transformer i have. Maybe i should stick to IRF640 anyway.

I wonder if its possible to use two IRF640 per side or if that is too mutch for the IR2010 gate drivers.

[MOER]

At these high voltages the IRF640 will fail if the switching freq is over 100KHz. The IR2110/2113 will drive many fets.

We use it in a current production model (Minilith) rated at 600w at 1 ohm and I use 4+4 IRF640N off a IR2113 BUT I run the triangle at 80KHz

www.zedaudio.com

[BWRX]

It's interesting to note that the UCD180 modules from Hypex use a pair of STP14NF10 in the output stage.

[Tekko]

I bought ten IRF640.

[johnwu22]

Hi,
Could anybody share his experience of using IRFB4020 as Class D power Mosfet?

Please refer to the attached power stage circuit.
Switching Frequency is about 330KHZ. The maximum output power is 120W with 3.5 £[ dummy load. The problem is that it is hot like class AB amplifier when it works. I¡¦ve tried to make dead time longer, but nothing changed.
Mosfet is IRFP250; Gate Driver is IR2010.

Also, I guess it should be the switching loss. In order to reduce switching loss, I tried to use much faster MOSFET IRFB4020 instead with dead time of 27ns. Unfortunately, they was damaged in one minute.
Many thanks

John Wu