Patent ID: 7781912

Claim:
A circuit, comprising: a first power source connected to a first opto-electric coupler; a first line configured to provide a control signal related to a second power source, the first line being connected to a second opto-electric coupler; and logic for emitting a second control signal for switching between the first power source and the second power source upon a change in state of at least one of the first or second opto-electric couplers; wherein the first opto-electric coupler is connected in parallel with a capacitor, and wherein a transistor of the first opto-electric coupler is connected to an input of a logic gate; and wherein the input of the logic gate is connected to a resistor, wherein the resistor is connected to a reference potential, and wherein the resistor and the capacitor are so dimensioned that a voltage tail begins at the input of the logic gate, as measured against the reference potential, during a negative half-cycle of the first power source.