Electronic – Dual N/P-Channel MOSFET Dies with Smoke

Madmanguruman and David Tweed are probably on the right track here.

Here is a scenario:

When the circuit starts the synchronous FET (T2) will be on. It has to be this way because there is no bias voltage for the high side drive for T1 except through T2. So, T2 sinks current from the battery through the inductor. Then finally T2 turns off. It doesn't matter if T1 turns on or not, the inductor dumps current back through T1 (or its body diode). The current has to go some place. SMPS are 1 quadrant devices (almost always), so the Laptop supply sinks nothing. The current can only go into C5 and Vcc of the IR2104, which has a max supply voltage rating of 25V. Boom.

To invert your signal, use another transistor.

^{simulate this circuit – Schematic created using CircuitLab}

Any of the BJTs will work. I'm personally partial to the 2N3904, but that's habit more than anything. Of the MOSFETs, I'd recommend first the IRF520, then the RFP70N06, and the IRF510 last, although any of them will work. If you use the IRF510, a heat sink on each one is a very good idea. With the IRF520, the worst-case power dissipation (LED on 100%) will be about 1 watt, so a heat sink is a good idea but not required.

The smoothing circuit link is worrying unnecessarily about response time.