Patent ID: 8736142

Claim:
A polarity switching circuit for converting a DC high voltage into an output AC voltage for driving a piezoelectric actuator, comprising: a first current-limiting resistor connected to the DC high voltage; a second current-limiting resistor connected to the DC high voltage; a first transistor switch having a control terminal receiving a first pulse-width modulating signal, a current input terminal connected to the first current-limiting resistor and the DC high voltage, and a current output terminal connected to a ground terminal directly; a second transistor switch having a control terminal receiving the first pulse-width modulating signal, a current input terminal, and a current output terminal connected to the ground terminal; a third transistor switch having a control terminal connected to the current input terminal of the first transistor switch and the first current-limiting resistor, a current input terminal connected to the DC high voltage, and a current output terminal connected to the current input terminal of the second transistor switch; a fourth transistor switch having a control terminal receiving a second pulse-width modulating signal, a current input terminal connected to the DC high voltage through the second current-limiting resistor, and a current output terminal connected to the ground terminal directly; a fifth transistor switch having a control terminal receiving the second pulse-width modulating signal, a current input terminal, and a current output terminal connected to the ground terminal; a sixth transistor switch having a control terminal connected to the current input terminal of the fourth transistor switch and the second current-limiting resistor, a current input terminal connected to the DC high voltage, and a current output terminal connected to the current input terminal of the fifth transistor switch; a first filter connected to the current input terminal of the second transistor switch, the current output terminal of the third transistor switch, a first contact of the piezoelectric actuator, and the ground terminal; and a second filter connected to the current input terminal of the fifth transistor switch, the current output terminal of the sixth transistor switch, a second contact of the piezoelectric actuator, and the ground terminal; wherein when the first pulse-width modulating signal and the second pulse-width modulating signal are alternately and respectively switching between a high level and a low level, the first filter and the second filter are configured to filter the output AC voltage into a smoothed AC waveform, thereby providing an output AC voltage with a smoothed waveform for the piezoelectric actuator.