| 摘要 |
A sounder has a drive coil (40) which receives a varying drive signal from a drive circuit. The magnetic field resulting therefrom drives an armature (12) which is mounted on a diaphragm (10) which produces sound due to the vibration thereof. A second coil (42) is magnetically and electrically connected to the drive coil (40). A diode (D1) is connected in series with the second coil and is arranged such that no current flows in the second coil (42) when the drive signal (which is unipolar) generates a current in the drive coil (40). When the drive signal is cut off, a current flows in the second coil (42) and charge is stored in a capacitor C1. The energy thus stored may be used to power the drive circuit. In this way, the power used by the sounder corresponds to the losses in the circuit and due to the acoustic power radiated by the sounder. Since this is only a small proportion of the power needed to drive the drive coil (40), the sounder is efficient.
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