3 chips lost by single button press

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mshh

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in the attached circuit i use analog signal to drive buck converter by atmega8 and it was working well . i connected MCP617 on the same breadboard to measure current in the circuit using zero ohm resistor . supply for atmega8 and the op amp from lm7805 where the input for lm7805 is 12 volt which was used as supply for IR2112 . when i add the op amp circuit i forgot to connect the negative terminal of the load to pin 3(+ve input) of the op amp then i switched on the power supply or the battery .i couldn't even see any signal the driver got very hot and the op amp ,but the atmega 8 didn't get hot but there was no output from it. i don't know what happened ,why did i lose the three ICs
 

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Your mishap sounds as though a high-voltage spike was created at startup, which fused the innards of the IC's, so they heated up due to conducting overmuch current.

The spike must have come from your coil.

I guess your schematic shows the proper layout so I don't know for sure...
But an improper connection (load or otherwise) can cause the coil to see high impedance at some point, causing it to generate a spike.
 


the coil burnt the driver before when i removed the free wheeling diode while working by false . but now the diode should prevent the spikes as it hasn't been moved. even if it was the spikes from the coil it should burn just the driver not the atmega and the op amp
 

Further items:

1. With no diode connected, the inductor can generate a ringing spike of several hundred V repeatedly (according to my simulation).

2. Op amp inputs (all or some) should not receive a voltage outside of the supply rails (either positive or negative). I don't know that this caused your problem.

3. With a light load and small smoothing capacitor, at the moment of start-up, my simulations show (a) positive and negative ringing across the coil, and (b) a spike of 2x the supply V across the load. Your schematic does not indicate you would have this problem, but with breadboards it is hard to verify all connections are solid.
 

"Should" is not a good engineering word.

Yeah, you can put a diode to shunt kickback current.
Where "should" that current go, you may think you
know. But it's sharp and your model of the current loop
and the voltages around it, maybe not so accurate in
the time domain as your conception of it. Series R,
series L, high dI/dt, jack the ground and latch up a part
somewhere else?

So no more yammering about "should". Probe it, prove it,
fix it better next time, repeat.
 

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