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 operating frequency generated by the voltage-controlled oscillator in another power supply circuit.

What is claimed is: 
     
       1. A power supply apparatus with a plurality of voltage output circuits each having a piezoelectric transformer and an oscillator which generates a signal for driving the piezoelectric transformer and for controlling an output voltage of the piezoelectric transformer, comprising:
 a frequency-dividing circuit which divides a frequency of the signal generated by the oscillator in at least one of the plurality of voltage output circuits, and outputs a driving frequency signal for driving the piezoelectric transformer in said at least one voltage output circuit,   wherein the frequency of the signal generated by the oscillator in said at least one voltage output circuit is larger than a frequency of the signal generated by the oscillator in another of the plurality of voltage output circuits.   
     
     
       2. The apparatus according to  claim 1 , wherein the frequency-dividing circuit divides the frequency of the signal in accordance with a frequency division ratio which can be arbitrarily set in accordance with a signal from an external device. 
     
     
       3. The apparatus according to  claim 1 , further comprising a detecting circuit which detects a magnitude of an interference frequency,
 wherein the frequency-dividing circuit divides the frequency of the signal in accordance with a frequency division ratio which is controlled based on the interference frequency.   
     
     
       4. The apparatus according to  claim 1 , wherein the oscillator and the frequency-dividing circuit include discrete components. 
     
     
       5. The apparatus according to  claim 1 , wherein the oscillator and the frequency-dividing circuit include integrated semiconductor IC devices. 
     
     
       6. An image forming apparatus comprising:
 an image forming unit adapted to form a image; and   a power supply unit adapted to output voltages to said image forming unit,   wherein said power supply unit comprises a plurality of voltage output circuits each having a piezoelectric transformer and an oscillator which generates a signal for driving the piezoelectric transformer and for controlling an output voltage of the piezoelectric transformer,   wherein at least one of the plurality of voltage output circuits has a frequency-dividing circuit which divides the frequency of the signal generated by the oscillator in said at least one voltage output circuit, and   wherein the frequency of the signal generated by the oscillator in said at least one voltage output circuit is larger than a frequency of the signal generated by the oscillator in another of the plurality of voltage output circuits.   
     
     
       7. The image forming apparatus according to  claim 6 , wherein said image forming unit includes a plurality of image forming stations, and
 wherein said plurality of voltage output circuits output voltages to each of said plurality of image forming stations.   
     
     
       8. The image forming apparatus according to  claim 7 , wherein each of said plurality of image forming stations is a circuit for forming a different color image. 
     
     
       9. A power supply comprising:
 a first and a second voltage output part which each include a piezoelectric transformer, a driving part adapted to drive the piezoelectric transformer, and an oscillation part adapted to output a frequency signal for driving the driving part, wherein   the first voltage output part outputs a voltage to a first process part which performs a process operation for forming an image, and the second voltage output part outputs a voltage to a second process part which differs from the first process part and performs a process operation for forming the image,   wherein the first process part is one of a first charging part adapted to execute a charging operation for charging a first photosensitive member, a first developing part adapted to execute a developing operation for developing a latent image formed on the first photosensitive member, and a first transferring part adapted to execute a transferring operation for transferring an image formed on the first photosensitive member,   the second process part is one of a second charging part adapted to execute a charging operation for charging a second photosensitive member, a second developing part adapted to execute a developing operation for developing a latent image formed on the second photosensitive member, and a second transferring part adapted to execute a transferring operation for transferring an image formed on the second photosensitive member,   each of the oscillation part of the first voltage output part and the oscillation part of the second voltage output part outputs the frequency signal having a frequency higher than each driving frequency of the driving part of the first voltage output part and the driving part of the second voltage output part,   the first voltage output part includes a first frequency-dividing part adapted to divide the frequency signal output from the oscillation part of the first voltage output part,   the second voltage output part includes a second frequency-dividing part adapted to divide the frequency signal output from the oscillation part of the second voltage output part,   the driving part of the first voltage output part drives the piezoelectric transformer in accordance with a driving signal output from the first frequency-dividing part, and   the driving part of the second voltage output part drives the piezoelectric transformer in accordance with a driving signal output from the second frequency-dividing part.   
     
     
       10. The power supply according to claim 9, wherein each of the first and the second voltage output parts includes a feedback part which detects a voltage output from the piezoelectric transformer and controls a frequency of the frequency signal output from the oscillation part in accordance with the detected voltage. 
     
     
       11. The power supply according to claim 10, wherein the feedback part detects the voltage output from the piezoelectric transformer as a lower detected voltage and feeds back the lower detected voltage to the oscillation part. 
     
     
       12. The power supply according to claim 11, wherein the feedback part feeds back, to the oscillation part, a comparison result between the lower detected voltage and a setting signal used for controlling the voltage output from the piezoelectric transformer so as to become a constant voltage. 
     
     
       13. The power supply according to claim 9, wherein a frequency of the frequency signal is equal to or more than twice the driving frequency. 
     
     
       14. An integrated circuit controls a power supply which comprises a first and a second voltage output part each including a piezoelectric transformer and a driving part adapted to drive the piezoelectric transformer, wherein the first voltage output part outputs a voltage to a first process part which performs a process operation for forming an image, and the second voltage output part outputs a voltage to a second process part which differs from the first process part and performs a process operation for forming the image, and wherein the first process part is one of a first charging part adapted to execute a charging operation for charging a first photosensitive member, a first developing part adapted to execute a developing operation for developing a latent image formed on the first photosensitive member, and a first transferring part adapted to execute a transferring operation for transferring an image formed on the first photosensitive member, the second process part is one of a second charging part adapted to execute a charging operation for charging a second photosensitive member, a second developing part adapted to execute a developing operation for developing a latent image formed on the second photosensitive member, and a second transferring part adapted to execute a transferring operation for transferring an image formed on the second photosensitive member, said integrated circuit further comprising:
 a first oscillation part adapted to output a frequency signal to the driving part of the first voltage output part;   a second oscillation part adapted to output a frequency signal to the driving part of the second voltage output part;   wherein each of the oscillation part of the first voltage output part and the oscillation part of the second voltage output part outputs the frequency signal having a frequency higher than each driving frequency of the driving part of the first voltage output part and the driving part of the second voltage output part,   a first frequency-dividing part adapted to divide the frequency signal output from the first oscillation part; and   a second frequency-dividing part adapted to divide the frequency signal output from the second oscillation part.   
     
     
       15. The integrated circuit according to claim 14, wherein each of the first and the second voltage output parts includes a feedback part which detects a voltage output from the piezoelectric transformer and controls a frequency of the frequency signal output from the oscillation part in accordance with the detected voltage. 
     
     
       16. The integrated circuit according to claim 15, wherein the feedback part detects the voltage output from the piezoelectric transformer as a lower detected voltage and feeds back the lower detected voltage to the oscillation part. 
     
     
       17. The integrated circuit according to claim 15, wherein the feedback part feeds back, to the oscillation part, a comparison result between the lower detected voltage and a setting signal used for controlling the voltage output from the piezoelectric transformer so as to become a constant voltage. 
     
     
       18. The integrated circuit according to claim 14, wherein a frequency of the frequency signal is equal to or more than twice the driving frequency. 
     
     
       19. An image forming apparatus comprising:
 a first process part configured to perform a process operation for forming an image;   a second process part configured to perform a process operation for forming the image, the second process part being different from the first process part;   wherein the first process part is one of a first charging part adapted to execute a charging operation for charging a first photosensitive member, a first developing part adapted to execute a developing operation for developing a latent image formed on the first photosensitive member, and a first transferring part adapted to execute a transferring operation for transferring an image formed on the first photosensitive member, the second process part is one of a second charging part adapted to execute a charging operation for charging a second photosensitive member, a second developing part adapted to execute a developing operation for developing a latent image formed on the second photosensitive member, and a second transferring part adapted to execute a transferring operation for transferring an image formed on the second photosensitive member, and   a power supply configured to include a first voltage output part for outputting a voltage to the first process part, and a second voltage output part for outputting a voltage to the second process part,   wherein the first and the second voltage output part each include a piezoelectric transformer, a driving part adapted to drive the piezoelectric transformer, and an oscillation part adapted to output a frequency signal for driving the driving part,   wherein each of the oscillation part of the first voltage output part and the oscillation part of the second voltage output part outputs the frequency signal having a frequency higher than each driving frequency of the driving part of the first voltage output part and the driving part of the second voltage output part,   wherein the first voltage output part includes a first frequency-dividing part adapted to divide the frequency signal output from the oscillation part of the first voltage output part, and   the second voltage output part includes a second frequency-dividing part adapted to divide the frequency signal output from the oscillation part of the second voltage output part, and   wherein the driving part of the first voltage output part drives the piezoelectric transformer in accordance with a driving signal output from the first frequency-dividing part, and   the driving part of the second voltage output part drives the piezoelectric transformer in accordance with a driving signal output from the second frequency-dividing part.   
     
     
       20. The image forming apparatus according to claim 19, wherein each of the first and the second voltage output parts includes a feedback part which detects a voltage output from the piezoelectric transformer and controls a frequency of the frequency signal output from the oscillation part in accordance with the detected voltage. 
     
     
       21. The image forming apparatus according to claim 20, wherein the feedback part detects the voltage output from the piezoelectric transformer as a lower detected voltage and feeds back the detected voltage to the oscillation part. 
     
     
       22. The image forming apparatus according to claim 20, wherein the feedback part feeds back, to the oscillation part, a comparison result between the detected voltage and a setting signal used for controlling the voltage output from the piezoelectric transformer so as to become a constant voltage. 
     
     
       23. The image forming apparatus according to claim 19, wherein each of the first process part and the second process part is a part adapted to form a different color image. 
     
     
       24. The image forming apparatus according to claim 19, wherein a frequency of the frequency signal is equal to or more than twice the driving frequency.