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Trying to build/design a Class D amp from a spec drawing, with a minor tweak.

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pompeiisneaks:
Hello,

I've just finished building and ruining my IRS2092 based Class D amp.  It was based on their example circuit I'll link here.  That circuit has one difference from mine, in that I had some 48VDC power supplies for the B+ and B- so I made sure I changed the MOSFET's to support that. 

First the schematic as I got it from Infineon with their recommended parts. 

The only change I made as mentioned was to use +/-48V and I replaced the mosfets with some STP40NF10 that support up to 100VDC and 50A that should handle the 48V just fine. 

Upon power up,  (I sent the 12VDC into the pin 12 via my bench power supply plus those B+/B- voltages) I only heard a periodic slow 'tic' noise and that's it.  I did realize, upon review that although I had my input jack connected to the gnd side of the jack, I didn't have the input side linked to the common GND of the rest of the schematic.  When I did so, I got a slight change in noise and then the magic smoke came out.  I blew the IRS2092. 

On reviewing voltages everything seemed ok, and the pins on the IRS2092 have all high level voltage allowances except for the VREF on pin 7, which seems to want between 4.8 to 5.4 and I did read about 9VDC there. 

Now, I'm thinking per what I read there, that the 5V is an output reference voltage but I'm not 100% sure if the R3/R5 is supposed to be a voltage drop/divider to provide the right voltage and expected the -35VDC into it to give the expected 5V range?  Is that why I smoked it? 

I also seem to have destroyed the mosfets, but I think that may have been a mistake I made after I removed the class d chip from my circuit and tried to power it again to read some static voltages?  Not sure.

At any rate, before I buy the replacement parts I thought I'd hit the hive mind and see what seems off with the changes to the schematic etc?

Edit: thought I'd add a link to mouser where I have the BOM for the parts I used for more detail. https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=d6e7fc6c1b

Thanks,

~Phil


pompeiisneaks:
Here's the updated schematic with the 48V and the new mosfets..

Circlotron:

--- Quote from: pompeiisneaks on August 17, 2020, 06:16:42 pm ---I also seem to have destroyed the mosfets, but I think that may have been a mistake I made after I removed the class d chip from my circuit and tried to power it again to read some static voltages?  Not sure.

--- End quote ---
Big mistake to power it up with the controller chip removed and the mosfet gates just floating. The gates may drift high and turn both devices partially on and before you know it they are smoking...

pompeiisneaks:

--- Quote from: Circlotron on August 18, 2020, 06:02:58 am ---
--- Quote from: pompeiisneaks on August 17, 2020, 06:16:42 pm ---I also seem to have destroyed the mosfets, but I think that may have been a mistake I made after I removed the class d chip from my circuit and tried to power it again to read some static voltages?  Not sure.

--- End quote ---
Big mistake to power it up with the controller chip removed and the mosfet gates just floating. The gates may drift high and turn both devices partially on and before you know it they are smoking...

--- End quote ---

That part makes sense, what I don't understand is why I cooked the IRS2092... the ticking at first seems likely to be a power on, safety shutdown cycle, but when I finally correctly grounded the input side it smoked the IC instantly.

~Phil

pompeiisneaks:
Maybe this is the wrong subforum for this?  Does it maybe fall under something about learning etc?  Or is this just an area that's not well documented?  Not many people interested?

Or am I not giving enough information?

~Phil

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