Pulse frequency modulation drive circuit for piezoelectric transformer

A differential pulse frequency modulation drive circuit for a piezoelectric device, comprising:

• a piezoelectric device having a resonant frequency and comprising a first input, a second input and an effective capacitance between the first input and the second input;
• a first inductor having a first end and a second end, the first inductor resonating with the effective capacitance of the piezoelectric device at the resonant frequency of the piezoelectric device, wherein the first end of the first inductor is coupled to the first input of the piezoelectric device;
• a second inductor having a first end and a second end, the second inductor resonating with the effective capacitance of the piezoelectric device at the resonant frequency of the piezoelectric device, wherein the first end of the second inductor is coupled to the second input of the piezoelectric device;
• a first switch coupled between ground and the first input of the piezoelectric device, said first switch being opened and closed by a periodic first signal at substantially a 50% duty factor of the resonant frequency of said piezoelectric device;
• a second switch coupled between the second end of the first inductor and a DC power supply, said second switch closing and opening in response to a non-periodic second signal synchronized with the opening and closing of said first switch;
• a third switch coupled between the second input of the piezoelectric device and ground, said third switch being opened and closed by a periodic third signal substantially 180.degree. out-of-phase with said first switch and at substantially a 50% duty factor of the resonant frequency of said piezoelectric device;
• a fourth switch coupled between the second end of the second inductor and the DC power supply, said fourth switch closing and opening in response to a non-periodic fourth signal substantially 180.degree. out-of-phase with said second switch and synchronized with the opening and closing of said third switch;
• an oscillator coupled to said piezoelectric device and operating at substantially the resonant frequency of the piezoelectric device for providing an output signal, said periodic first and third signals being generated in response to said output signal;
• and
• said non-periodic second and fourth signals being generated in response to an asynchronous control signal such that the closing of said second and fourth switches gates an integral number of substantially half sinewave resonant waveforms having substantially zero switching volts across the input of the piezoelectric device.

A single ended pulse frequency modulation drive circuit for a piezoelectric transformer, comprising:

• a piezoelectric transformer having a resonant frequency and comprising a first input, a second input connected to ground, an effective capacitance between the first input and the second input, and an output section coupled to a load;
• an inductor having a first end and a second end, the inductor resonating with the effective capacitance of the piezoelectric transformer at the resonant frequency of the piezoelectric transformer, wherein the first end of the inductor is coupled to the first input of the piezoelectric transformer;
• a first switch coupled between ground and the first input of the piezoelectric transformer and operated by a periodic first signal at substantially a 50% duty factor of the resonant frequency of the piezoelectric transformer;
• an oscillator coupled to said piezoelectric transformer and operating at substantially the resonant frequency of the piezoelectric transformer for providing an output signal, said periodic first signal generated in response to said output signal;
• and
• a second switch coupled between the second end of the inductor and a DC power supply, said second switch closing and opening in response to a non-periodic second signal synchronized with the opening and closing action of said first switch, said second signal being generated in response to an asynchronous control signal such that the closing of said second switch gates an integral number of substantially half sinewave resonant waveforms having substantially zero switching volts across the input of the piezoelectric transformer.

A differential pulse frequency modulation drive circuit for a piezoelectric transformer, comprising:

• a piezoelectric transformer having a resonant frequency and comprising a first input, a second input connected to ground and an effective capacitance between the first input and the second input and an output section coupled to a load;
• a first inductor having a first end and a second end, the first inductor resonating with the effective capacitance of the piezoelectric transformer at the resonant frequency of the piezoelectric transformer, wherein the first end of the first inductor is coupled to the first input of the piezoelectric transformer;
• a second inductor having a first end and a second end, the second inductor resonating with the effective capacitance of the piezoelectric transformer at the resonant frequency of the piezoelectric transformer, wherein the first end of the second inductor is coupled to the second input of the piezoelectric transformer;
• a first switch coupled between ground and the first input of the piezoelectric transformer, said first switch being opened and closed by a periodic first signal at substantially a 50% duty factor of the resonant frequency of said piezoelectric transformer;
• a second switch coupled between the second end of the first inductor and a DC power supply, said second switch closing and opening in response to a non-periodic second signal synchronous with the opening and closing of said first switch;
• a third switch coupled between the second input of the piezoelectric transformer and ground, said third switch being opened and closed by a periodic third signal substantially 180.degree. out-of-phase with said first switch and at substantially a 50% duty factor of the resonant frequency of said piezoelectric transformer;
• a fourth switch coupled between the second end of the second inductor and the DC power supply, said fourth switch closing and opening in response to a non-periodic fourth signal substantially 180.degree. out-of-phase with said second switch and synchronized with the opening and closing of said third switch;
• an oscillator coupled to said piezoelectric transformer operating at substantially the resonant frequency of the piezoelectric transformer for providing an output signal, said periodic first and third signals being generated in response to said output signal;
• and
• said non-periodic second and fourth signals being generated in response to an asynchronous control signal such that the closing of said second and fourth switches gate an integral number of substantially half sinewave resonant waveforms having substantially zero switching volts across the input of the piezoelectric transformer.