POWER SUPPLY APPARATUS, AND IMAGE FORMING APPARATUS HAVING THE SAME

Abstract

A power supply apparatus with a plurality of power supply circuits each having a piezoelectric transformer and a voltage-controlled oscillator which generates a signal at an operating frequency used to drive the piezoelectric transformer in accordance with a control signal, includes a frequency-dividing circuit which divides the operating frequency generated by a voltage-controlled oscillator in at least one power supply circuit, and outputs a signal at a driving frequency to drive a piezoelectric transformer in the one power supply circuit. When at least one power supply circuit and remaining power supply circuits output voltages, the operating frequency generated by the voltage-controlled oscillator in the one power supply circuit is controlled to be higher than the driving frequency.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing the arrangement of a transfer high-voltage power supply using a piezoelectric transformer according to the first embodiment;

FIG. 2 is a view showing the arrangement of an image forming apparatus having a high-voltage power supply apparatus using a piezoelectric transformer according to the first embodiment;

FIG. 3 is a circuit diagram for explaining the schematic mechanism of the occurrence of interference, and showing the arrangement of the transfer high-voltage power supply using the piezoelectric transformer;

FIG. 4 is a graph showing the relationship between the output voltage (V) and the driving frequency (Hz) as a characteristic of the piezoelectric transformer;

FIG. 5 is a graph showing the relationship between the driving frequencies fx1 and fx2 (Hz) and the output voltage (V);

FIG. 6 is a graph showing effects obtained when the transfer high-voltage power supply includes a frequency-dividing circuit according to the first embodiment;

FIG. 7 is a circuit diagram showing the arrangement of a transfer high-voltage power supply using a piezoelectric transformer according to the second embodiment;

FIG. 8 is a table for explaining the setting of a frequency division ratio in the transfer high-voltage power supply using the piezoelectric transformer according to the second embodiment;

FIG. 9A is a graph showing the relationship between a bias voltage (control output voltage Edc) and a driving frequency;

FIG. 9B is a partial enlarged view of an area 901 surrounded by a broken line in FIG. 9A;

FIG. 10 is a circuit diagram showing the arrangement of a transfer high-voltage power supply using a piezoelectric transformer according to the third embodiment;

FIG. 11 is a block diagram showing the arrangement of a detecting circuit arranged in a Y-station high-voltage circuit in the transfer high-voltage power supply using the piezoelectric transformer according to the third embodiment;

FIG. 12A is a timing chart showing a signal input to a detecting circuit;

FIG. 12B is a timing chart showing a low-pass filter output obtained by cutting off a high-frequency component;

FIG. 12C is a timing chart showing a signal output from the detecting circuit; and

FIG. 13 is a circuit diagram showing a conventional high-voltage power supply circuit using a piezoelectric transformer.

Claims

1. A power supply apparatus with a plurality of power supply circuits each having a piezoelectric transformer and a voltage-controlled oscillator which generates a signal at an operating frequency used to drive the piezoelectric transformer in accordance with a control signal, comprising: a frequency-dividing circuit which divides the operating frequency generated by a voltage-controlled oscillator in at least one power supply circuit, and outputs a signal at a driving frequency to drive a piezoelectric transformer in said one power supply circuit,wherein when said at least one power supply circuit and remaining power supply circuits output voltages, the operating frequency generated by the voltage-controlled oscillator in said one power supply circuit is controlled to be higher than the driving frequency.

2. The apparatus according to claim 1, wherein a frequency division ratio of the frequency-dividing circuit can be arbitrarily set in accordance with a signal generated by an external circuit.

3. The apparatus according to claim 1, further comprising a detecting circuit which detects a magnitude of an interference frequency component between the driving frequency of the piezoelectric transformer in said one power supply circuit and the driving frequencies of the piezoelectric transformers in said remaining power supply circuits, wherein a setting of the frequency division ratio of said frequency-dividing circuit is controlled based on a detection result obtained by said detecting circuit.

4. The apparatus according to claim 1, wherein said voltage-controlled oscillator and said frequency- dividing circuit include discrete components.

5. The apparatus according to claim 1, wherein said voltage-controlled oscillator and said frequency- dividing circuit include integrated semiconductor IC devices.

6. An image forming apparatus comprising: a power supply apparatus defined in claim 1; andan image forming unit adapted to form a toner image,wherein said image forming unit uses a voltage supplied from the power supply apparatus,