The present invention relates to a power supply device, and in particular to a power supply device capable of supplying high and low voltages.
Certain apparatus such as copying machine or laser beam printer require a high voltage supply for example for a charger, and a low voltage supply for control unit such as a microprocessor for controlling the operation sequency of the apparatus.
In such apparatus it has been customary to convert the commercial power supply to a low voltage of the order of 24V, to stabilize the low voltage, and to guide the voltage to a high voltage power supply device for voltage elevation and rectification.
Instead of an integral power supply unit for high and low voltages as in television receivers, the above-explained structure is adopted in order to control the high voltage supply by a control unit operated by a low voltage supply, to simplify the structure of the high voltage supply unit, and to meet the conditions of insulation required by various standards.
However the above-explained structure requires plural separate power supply units, and is therefore complex and expensive. It is thus difficult to reduce the cost, dimension and weight of the power supply. Also such a structure is undesirable in terms of power efficiency, particularly on the high voltage side. Such drawback is not limited to copying machines but exists commonly in any apparatus that requires high and low voltages and has to control the high voltage supply.
The control of the high voltage supply is indispensable since continuous high voltage supply is not only undesirable in terms of power consumption but also leads to the deterioration of the charger, the photosensitive drum etc., in case of a copy machine.