In described examples, a first isolation element electrically isolates a first circuit from a second circuit and passes AC signals between the first circuit and the second circuit. A second isolation element electrically isolates the first circuit from the second circuit and passes AC signals between the first circuit and the second circuit. A ground of the second circuit electrically floats relative to a ground of the first circuit, so that a digital signal is able to pass from the second circuit through a third isolation element to the first circuit. A supply voltage generation device converts AC signals from the first isolation element and the second isolation element into at least one DC voltage to power the second circuit.