US 5,705,895 A · Power circuit with duty conversion circuit for driving a capacitive load

Abstract

A power terminal is connected to a DC power source. A differential amplifier has primary and secondary input terminals and an output terminal, and a device applies a reference voltage to the secondary input terminal of the differential amplifier. A phase inverter has an input terminal connected to the output terminal of the differential amplifier and has primary and secondary output terminals that output two output signals of opposite phase. A push-pull drive circuit has primary and secondary input terminals connected to the primary and secondary output terminals of the phase inverter, and has primary and secondary output terminals connected to a switching element that alternately turns on and off by being driven by the two output signals of opposite phase that are provided from the output terminals of the phase inverter. An autotransformer has a tap connected to the power terminal and taps, provided at both sides of the tap connected to the power terminal, that are connected to the primary and secondary output terminals at the push-pull drive circuit, respectively. A capacitive load may be connected at both sides of the autotransformer. A positive feedback path connects one terminal of the autotransformer to the primary input terminal of the differential amplifier, and a sinusoidal AC voltage is applied to the capacitive load. A duty ratio conversion circuit automatically changes the duty ratio of drive signals for the push-pull drive circuit according to the resonance frequency that is determined by the inductance of the autotransformer and the capacitance of the capacitive load. The duty ratio conversion circuit is connected between the phase inverter and the push-pull drive circuit.

Claims21

Dependent claims

A power circuit comprising:

a differential amplifier having first and second inputs and an output, the first input being connected to receive a first voltage;
a phase inverter having an input connected to receive the output of said differential amplifier and having first and second outputs with first and second phases;
a push-pull drive circuit having first and second inputs and first and second outputs;
a feedback path coupling the first output of said push-pull drive circuit to the second input of said differential amplifier;
an autotransformer having first and second ends coupled between the first and second outputs of said push-pull drive circuit, said autotransformer having a tap connected to a source of a second voltage that is higher than the first voltage;
a capacitive load attached to the first and second ends of said autotransformer, a resonance frequency being determined by inductance of said autotransformer and capacitance of said load;
and
a duty ratio conversion circuit having first and second inputs connected to the first and second outputs of said phase inverter and having first and second outputs connected to the first and second inputs of said push-pull drive circuit, said duty ratio conversion circuit changing a duty ratio of signals input to said push-pull drive circuit in response to a change in the resonance frequency.

5 more elements

A power circuit comprising:

a power terminal connected to a DC power source;
a differential amplifier that has primary and secondary input terminals and an output terminal;
a device that applies a reference voltage to the secondary input terminal of said differential amplifier;
a phase inverter that has an input terminal connected to the output terminal of said differential amplifier and primary and secondary output terminals that output two output signals of opposite phase;
a push-pull drive circuit that has primary and secondary input terminals, said push-pull circuit having primary and secondary output terminals that are connected to a switching element that alternately turns on and off by being driven by the two output signals of opposite phase and provided from the output terminals of the phase inverter;
an autotransformer with a tap that is connected to said power terminal and taps at both sides of the tap connected to said power terminal, the taps at both sides of the tap connected to said power terminal being connected to the primary and secondary output terminals at said push-pull drive circuit, respectively, in order for a capacitive load to be connected at both sides and such that a sinusoidal AC voltage is applied to the load, a resonance frequency being determined by inductance of said autotransformer and capacitance of the load;
a positive feedback path that connects one terminal of said autotransformer to the primary input terminal of said differential amplifier;
and
a duty ratio conversion circuit that has primary and secondary input terminals connected to the primary and secondary output terminals of said phase inverter, said duty ratio conversion circuit having primary and secondary output terminals that are connected to the primary and secondary input terminals of said push-pull drive circuit, said duty ratio conversion circuit changing a duty ratio of signals input to said push-pull drive circuit in response to a change in the resonance frequency.

6 more elements

Dependencies are inferred from the claim text.

Power circuit with duty conversion circuit for driving a capacitive load

Life of this patent

Power circuit with duty conversion circuit for driving a capacitive load

Life of this patent

Abstract

Claims21