Power supply device

Claim 2

A power supply device comprising: a transformer having a primary winding and a plurality of secondary windings comprising first and second secondary windings; switching means connected to said primary winding of said transformer for switching an input to said primary winding to generate an increased voltage output on said plurality of secondary windings of said transformer; first output means for applying a high voltage to a predetermined load in accordance with an output of said first secondary winding; second output means connected to said second secondary winding for outputting a predetermined low voltage; control means adapted to be supplied thereto with said predetermined low voltage from said second output means as an operation source, said control means producing a control signal for switching the high voltage supplied to said predetermined load from a first high voltage to a second high voltage; and change means responsive to said control signal for changing the electric power supplied to said primary winding.

Claim 3

A power supply device according to claim 1, wherein said second output means comprises rectifying means for rectifying the low-voltage output of said transformer and stabilizing means for stabilizing the output of said rectifying means to a constant low-voltage, wherein the output of said stabilizing means is supplied to said control means.

Claim 4

A power supply device according to claim 2, wherein sid stabilizing means comprises a switching regulator.

Claim 5

A power supply device according to claim 1, wherein said switching means comprises: an auxiliary power supply formed from a part of input; comparator means for comparing the output of the transformer with a pre-determined value for maintaining the output of the transformer constant; signal output means for releasing a signal of varying duty ratio according to the output of said comparator means; and a transistor for effecting a switching operation according to the output signal of said signal output means.

Claim 6

A power supply device according to claim 4, wherein said plurality of secondary windings include a third secondary winding, wherein the driving current for said transistor is supplied by a rectified output of the input power at the start of operation, and by said third secondary winding of said transformer after the operation is started.

Claim 7

A power supply device according to claim 1, wherein said pre-determined load is a charger of an image forming apparatus.

Claim 8

A power supply device according to claim 6, wherein said first high voltage is adapted to prevent charge current from flowing through said charger, and said second high voltage is adapted to permit charge current to flow through said charger.

Claim 9

A power supply device according to claim 7, wherein said first high voltage is applied to said charger at a time during which said image forming apparatus is in its stand-by state, and said second high voltage is applied to said charger at the time of image formation of said image forming apparatus.

Claim 10

A power supply device for image forming apparatus comprising: a transformer having a primary winding and a plurality of secondary windings including first and second secondary windings; switching means connected to said primary winding of said transformer for switching an input to said primary winding to generate an increased output voltage on said plurality of secondary windings of said transformer; first output means for outputting a high voltage to a charging means in accordance with an output of said first secondary winding; second output means for outputting a high frequency output to an exposure means in accordance with an output of said second secondary winding; third output means connected to said second secondary winding for outputting a regulated low voltage to a sequence control means; and change means responsive to a control signal from said sequence control means for changing the output voltage from said first output means between the time during which the image forming apparatus is in its stand-by state and the time of image formation of the image forming apparatus.

Claim 11

A power supply device for image forming apparatus comprising: a transformer having a primary winding and a plurality of secondary windings including first and second secondary windings; switching means connected to said primary winding of said transformer for switching an input to said primary winding to generate an increased output voltage on said plurality of secondary windings of said transformer; first output means for outputting a high voltage to a charging means in accordance with an output of said first secondary winding; second output means for outputting a high frequency output to an exposure means in accordance with an output of said second secondary winding; third output means connected to said second secondary winding for outputting a regulated low voltage to a sequence control means; and change means responsive to a control signal from said sequence control means for changing the output voltage from said first output means between the time during which the image forming apparatus is in its stand-by state and the time of image formation of the image forming apparatus.

Claim 12

A power supply device according to claim 9, wherein said change means changes the output voltage from said first output means so as to provide, at the time during which the image forming apparatus is in its stand-by state, a voltage which is adapted not to flow charge current through said charging means, and so as to provide, at the time of image formation, a voltage which is adapted to flow charge current through said charging means.

Claim 13

A power supply device according to claim 9, wherein said change means is operable to more than double the output voltage of said first secondary winding.

Claim 14

A power supply device comprising: a transformer having a primary winding and a plurality of secondary windings including first, second, and third secondary windings; switching means connected to said primary winding of said transformer for switching an input to said primary winding to generate an increased output voltage on said plurality of secondary windings of said transformer; first output means for applying a high voltage to a pre-determined load in accordance with an output of said first secondary winding; second output means for outputting a low voltage from said second secondary winding; third output means for outputting a low voltage from said third secondary winding; selection means for selecting the output of said second output means or said third output means; and control means adapted to be supplied with said low voltage from said second or third output means selected by said selection means as an operation source, said control means producing a control signal for controlling the high voltage outputted from said first output means.

Claim 15

A power supply device comprising: a transformer having a primary winding and a plurality of secondary windings including first, second, and third secondary windings; switching means connected to said primary winding of said transformer for switching an input to said primary winding to generate an increased output voltage on said plurality of secondary windings of said transformer; first output means for applying a high voltage to a pre-determined load in accordance with an output of said first secondary winding; second output means for outputting a low voltage from said second secondary winding; third output means for outputting a low voltage from said third secondary winding; selection means for selecting the output of said second output means or said third output means; and control means adapted to be supplied with said low voltage from said second or third output means selected by said selection means as an operation source, said control means producing a control signal for controlling the high voltage outputted from said first output means.

Claim 16

A power supply device according to claim 12, wherein said predetermined load is a charger of an image forming apparatus, and said control means produces the control signal for changing over the high voltage applied from said first output means to said charger between the time during which the image forming apparatus is in its stand-by state and the time of image formation of the image forming apparatus.

Claim 17

A power supply device according to claim 13, wherein said first output means outputs, at the time during which the image forming apparatus is in its stand-by state, the voltage which is adapted to prevent charge current from flowing through said charger, and outputs, at the time of image formation, a voltage which is adapted to permit charge current to flow through said charger.

Claim 18

A power supply device according to claim 13, wherein said selection means is operable, at the time during which the image forming apparatus is in its stand-by state, to apply the low voltage from said second output means to said control means, and at the time of image formation, to apply the low voltage from said third output means to said control means.