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 each including a piezoelectric transformer, a driving part configured to drive the piezoelectric transformer, and an oscillator configured to output a frequency signal for driving the driving part, and   wherein   the oscillator of the first voltage output part and the oscillator of the second voltage output part each output the frequency signal having a frequency higher than the driving frequencies of the driving part of the first voltage output part and of the driving part of the second voltage output part, wherein a frequency difference occurs between a driving frequency of the piezoelectric transformer of the first voltage output part and a driving frequency of the piezoelectric transformer of the second voltage output part, wherein   the first voltage output part includes a first frequency-dividing part configured to divide the frequency signal output from the oscillator of the first voltage output part, and   the second voltage output part includes a second frequency-dividing part configured to divide the frequency signal output from the oscillator of the second voltage output part, and   a frequency division ratio of the first frequency-dividing part and a frequency division ratio of the second frequency-dividing part are set according to the frequency difference.   
     
     
       10. The power supply according to claim 9, wherein the first and the second voltage output part each include a feedback part which detects a voltage output from the piezoelectric transformer, wherein the frequency of the frequency signal output from the oscillator is controlled 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 being lower than a voltage previously input into the oscillator and feeds back the detected voltage to the oscillator. 
     
     
       12. The power supply according to claim 11, wherein the feedback part feeds back, to the oscillator, 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. 
     
     
       13. The power supply according to claim 9, wherein the frequency division ratio of the first frequency-dividing part and the frequency division ratio of the second frequency-dividing part are each equal to or more than two. 
     
     
       14. The power supply according to claim 9, wherein the first frequency-dividing part outputs the divided frequency signal to the driving part of the first voltage output part, and the second frequency-dividing part outputs the divided frequency signal to the driving part of the second voltage output part. 
     
     
       15. The power supply according to claim 9, wherein the frequency of the frequency signal generated by the oscillator of the first voltage output part is close to the frequency of the frequency signal generated by the oscillator of the second voltage output part. 
     
     
       16. The power supply according to claim 9, wherein the frequency division ratio of the first frequency-dividing part and the frequency division ratio of the second frequency-dividing part are fixedly set so that the frequency difference is higher than a predetermined value. 
     
     
       17. The power supply according to claim 9, further comprising a detection circuit configured to detect the frequency difference,
 wherein the frequency division ratio of the first frequency-dividing part and the frequency division ratio of the second frequency-dividing part are variably set based on the frequency difference detected by the detection circuit.   
     
     
       18. An image forming apparatus comprising:
 a first image forming part;   a second image forming part; and   a power supply comprising a first and a second voltage output part each including a piezoelectric transformer, a driving part configured to drive the piezoelectric transformer, and an oscillator configured to output a frequency signal for driving the driving part, wherein the first voltage output part outputs a voltage to the first image forming part, and the second voltage output part outputs a voltage to the second image forming part output, and   wherein   the oscillator of the first voltage output part and the oscillator of the second voltage output part each output the frequency signal having a frequency higher than the driving frequencies of the driving part of the first voltage output part and of the driving part of the second voltage output part, wherein a frequency difference occurs between a driving frequency of the piezoelectric transformer of the first voltage output part and a driving frequency of the piezoelectric transformer of the second voltage output part, wherein   the first voltage output part includes a first frequency-dividing part configured to divide the frequency signal output from the oscillator of the first voltage output part, and   the second voltage output part includes a second frequency-dividing part configured to divide the frequency signal output from the oscillator of the second voltage output part, and   a frequency division ratio of the first frequency-dividing part and a frequency division ratio of the second frequency-dividing part are set according to the frequency difference.   
     
     
       19. The image forming apparatus according to claim 18, wherein the first and the second voltage output part each include a feedback part which detects a voltage output from the piezoelectric transformer, wherein the frequency of the frequency signal output from the oscillator is controlled in accordance with the detected voltage. 
     
     
       20. The image forming apparatus according to claim 19, wherein the feedback part detects the voltage output from the piezoelectric transformer as being lower than a voltage previously input into the oscillator and feeds back the detected voltage to the oscillator. 
     
     
       21. The image forming apparatus according to claim 20, wherein the feedback part feeds back, to the oscillator, 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. 
     
     
       22. The image forming apparatus according to claim 18, wherein the first and the second image forming part each include a charging part configured to charge an image carrier, a developing part configured to develop a latent image formed on the image carrier, or a transferring part configured to transfer an image formed on the image carrier. 
     
     
       23. The image forming apparatus according to claim 18, wherein the frequency division ratio of the first frequency-dividing part and the frequency division ratio of the second frequency-dividing part are each equal to or more than two. 
     
     
       24. The image forming apparatus according to claim 18, wherein the first frequency-dividing part outputs the divided frequency signal to the driving part of the first voltage output part, and the second frequency-dividing part outputs the divided frequency signal to the driving part of the second voltage output part. 
     
     
       25. The image forming apparatus according to claim 18, wherein the frequency of the frequency signal generated by the oscillator of the first voltage output part is close to the frequency of the frequency signal generated by the oscillator of the second voltage output part. 
     
     
       26. The image forming apparatus according to claim 25, wherein the first and the second image forming part each form an image, wherein the image includes density unevenness,
 the frequency of the frequency signal generated by the oscillator of the first voltage output part and the frequency of the frequency signal generated by the oscillator of the second voltage output part are higher than a frequency corresponding to a pitch of the density unevenness of the image.   
     
     
       27. The image forming apparatus according to claim 26, wherein the pitch of the density unevenness of the image is determined based on process speed of the first and the second image forming part and a difference between the driving frequencies of the driving parts of the first and the second voltage output parts. 
     
     
       28. The image forming apparatus according to claim 18, wherein the frequency division ratio of the first frequency-dividing part and the frequency division ratio of the second frequency-dividing part are fixedly set so that the frequency difference is higher than a predetermined value. 
     
     
       29. The image forming apparatus according to claim 18, further comprising a detection circuit configured to detect the frequency difference,
 wherein the frequency division ratio of the first frequency-dividing part and the frequency division ratio of the second frequency-dividing part are variably set based on the frequency difference detected by the detection circuit.