How did I kill 2 Mosfets?

[ants]

I sent the order last night, it was a fair few hours all in. I checked all of the packages were available without being too expensive but haven't ordered the components yet, I might want a few other bits and pieces before the board arrives. I tidied up a bit from the last pic, centering components and using a bit more copper. I remember trying to avoid using the via in the Vout plane but it entailed breaking the square of the ground plane and I thought, perhaps erroneously, keeping the ground plane surrounding everything was preferable. I will fix that on the next revision. I can see by comparison that the layout of the rest of the circuit degraded from the last revision. The opamp is quite robust and works almost perfectly on a stripboard, the 555 timer frequency does suffer from variations of trace capacitance but I have a trimmer in there to alter the frequency, I need that to tune in the piezo regardless, there are a fair few things to do for the next revision. The board will need debugging probably, I will fall over if it actually works!

Thanks,

Ant.

 

[ants]

I've had the manufacture pic back and should get the board in a few days. It looks ok, what I wasn't expecting is for the polygons not to have the chip pads inside them, it looks like the silkscreen didnt work exactly as I'd like. I have already begun work on the next revision which AC couples the opamp output. I'm also considering a final (hopefully) revision that uses the Max 773 DC booster rather than the Max770, I might require over 16.5V which will necessitate this, but I'm not sure at the moment.

Ant.

 

[ants]

I have made up the circuit, as I haven't made a smd board before it looks a mess but the DC booster worked like a charm. I was looking at the DC booster after it was done thinking that it couldn't possibly work, then I powered it up and I saw a little cloud of smoke appear off the MAX770 and thought that was no surprise and left for half an hour. I came back and noticed I had the battery on the wrong way! I put the battery on properly and it has been great ever since. The rest of the board isn't so good, I knew this beforehand, the whole idea of powering the opamp off a voltage divider wasn't good, it actually does work if I knock it on the bench top hard enough, I get the 180Vpp out of the transformer, but the signal isn't so good and it tends not to work. I have made up the next board pretty much and I think it will work just fine. I also needed to put on a switch and mount holes for the container. Thanks.

Ant.