A bridge circuit is usually used for operating an electrical load that has both an inductive and a capacitive component. The electrical load can be a piezo actuator, for example, and is operated with a voltage provided in the bridge branch. A piezo actuator has electrical and mechanical properties. The electrical component is represented in essence as a capacitor, a so-called parallel capacitor, while the mechanical component is depicted essentially as a series resonant circuit with a frequency-determining inductance. Such a piezo actuator is used, for example, to excite a loudspeaker membrane. Common driver circuits use so-called full bridges, which reach double the voltage amplitude of a half-bridge for the same supply voltage and, therefore, also roughly twice the amplitude of the mechanical movement generated by a connected piezo actuator.
Known driver circuits switch the bridge alternately in the forward and the reverse direction, with a voltage at the level of a positive supply voltage being provided in the bridge branch in the forward direction, and a voltage at the level of the negative supply voltage being provided in the bridge branch in the reverse direction. For this purpose it is necessary in each case to discharge the energy stored in the parallel capacitor, reverse the capacitor's polarity and recharge it. The power loss that occurs is roughly four times the product of the capacitance value of the parallel capacitor, the squared supply voltage and the switching frequency.