On 02/09/2010 10:06 PM, Abd ul-Rahman Lomax wrote: > At 09:55 PM 2/9/2010, Stephen A. Lawrence wrote: >> Large peak voltages when the circuit's opened, sure, I can buy that. >> But one thing inductors do really well is squash the current peaks. > > When you turn on the inductor, yes. But when you turn it off quickly, > the opposite. At least the voltage spikes, it tends to fry switches. > >> Look at Naudin's scope shots -- no wild peaks in the current, and I >> don't think that's because he "lost" them somewhere. They were never >> there to begin with. >> >> L * dI/dt = V >> >> I = integral(V/L) dt. >> >> In other words, you need a nice high voltage for a good long while to >> get a really hefty current to flow through an inductor. Forget Sean's >> high *current* transients, they're not happening. > > Yeah, I think you are right, on that end. Energy is stored in the > inductor field, but with relatively long rise time. When the switch > opens, though, the field collapse will recover some of that energy, and > quickly. Usually it's dumped through a diode to protect the switch.
Again, it's not a current spike, it's a voltage spike. In fact it's the opposite of a current spike: The current is like the Energizer bunny. It just keeps going, and going... no sharp spike, but no sharp dip either, and when you try to interrupt it, if there's no place else to go it'll go through an arc. And then your switch gets fried. > >
