LLC Resonant Converters & Plumbing?

llc_plumbingComparing electrical systems to plumbing is nothing new. Sure, one flows through closed circuits while the other flows out of faucets, but they are similar in a lot of ways. One of the similarities is the problems that can occur when a switch (or faucet) is closed abruptly. In poorly designed plumbing systems the sudden rise in pressure when a faucet is closed can cause a loud thump and eventually even damage the system. It’s called “water hammer,” and on a very small scale it’s the same phenomenon the navy uses to destroy submarines with depth charges. The problem is that water isn’t compressible and the energy of the sudden pressure-rise when a faucet is closed needs somewhere to go. A solution is to put an air damper in the system. The air damper returns most of the energy it absorbs, just not all at once.

Similarly, because electricity obeys the Law of Conservation of Energy, the sudden turning off of a switch in a square wave switching power conversion system produces a voltage spike that can be similarly damaging. The problem in electrical systems is more complicated than in plumbing since converters switch on and off thousands of times a minute and the effects of all those uncontrolled spikes on system efficiency and safety can be significant. A variety of approaches have been tried, but today one of the most effective is the use of an LLC converter, so called because it incorporates two inductors—LL—and a capacitor—C—to serve a similar function to a plumbing system’s air damper. LLC components preserve the energy in the systems but eliminate the voltage spike that occurs when you suddenly turn off the switch leaving the energy nowhere to go.

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