# DC2DC converters and Lenz's Law

someone told me that DC2DC is based on Lenz's Law, i couldn't figure out why DC2DC charge a capacitor and Lenz's Law is based on the change of the flux of the magnetic field over time.

can you please make some sense in this claim?

It's like saying cars work on Newton's principle of F=MA. It's true that they follow it, but to say that they're based on it is questionable. Because having the principle doesn't lead very directly to the device. Or, you could drive your baseball to work. DC2DC are based on so many Laws, there are too many to count. I call foul.

To delve more deeply, there are too many levels removed. Lenz's law give you a current/flux relationship, a current gives you a working coil, a coil gives you a transformer/inductor, that gives you the ability to modify voltages efficiently. It's just too indirect.

But is has more to do with what "based on" means.

A DC converter also has an inductor. (Well, most designs do. You probably could build one without an inductor but it wouldn't be very efficient so why bother?)

Lenzes law is just about the sign of induced EMF in an inductor (its really just a statement of energy conservation really).

The key law that is actually relevant is V.dt = L.dI, or put another way dI/dt = V/L the rate of change of current in the inductor depends on the voltage across it (ignoring losses and non-linearity and saturation). Inductors store energy of L/2 I^2

Its also important that there is an output capacitor, following I.dt = C.dV dV/dt = I/C capacitors store energy of C/2 V^2

A switch-mode supply is alternately pumping energy into the inductor, then out from it to the output capacitor, all without loss (in theory with perfect components). You arrange the output voltage oscillates about the wanted output value with a sufficiently small range (such as +/- 50mV), and you get high efficiency.

In real cored inductors the value of L drops by orders of magnitude if too much current flows and the magnetic circuit saturates - some circuitry in a DC-DC converter chip is about detecting saturation and preventing damage.