POOF!
So here’s the story: for my graduation project I need, amongst lots of other things, to drive a DC motor, which anyone who has some experience with building circuitry will tell you is not so big a deal. Except this motor is, because it typically requires around 4 amps to operate, which can go up to 6A when it’s moving a heavy load. Now this is not so much the problem, because I have the power supply required, but I just need to lower the voltage to make it go slower. Oh, and did I mention it’s reversible? I’m sure many hardware gurus will be scratching their chins right about now, going “hmmm”. I know I was, but then again I’m far from being a hardware guru, I’m just learning.
Anyway, back to the story. Apparently, lowering the voltage for a reversible DC motor whilst delivering 4 to 6 amps is not something that’s easily done. It needs a bunch of circuitry. Long story short: I meet this guy (Daniel, you rule) who likes to build circuitry in his spare time and he agrees to help me with this. So finally, after struggling on this problem for months (well, maybe not months and maybe not just this problem, but a long time anyway) I end up with a schematic of a circuit that simulates great in software and I build it on my breadboard (see pictures). I check, I double check, I measure with low voltage, I measure with the power supply I’ll be using, and it works. Woohoo, it works! And then I plug in the motor…
First, the motor starts moving hesitantly. Then it picks up a bit of speed and does what I want it to. It moves, and at exactly the right speed. I remember thinking: “Thank god, I’m done with this whole motor driving circuit thing”. But then I hear the nerve-wrecking *POOF!*. A lot of smoke, a vile smell and the sound of electrical sparks. I immediately pull the plug, but needless to say it was too late (as is often the case when you’ve witnessed your chip explode). Turns out I should have been cooling the chip…
circuit on the left, cracked chip with melt spots on the right (click to enlarge)