JP2637461B2 - Power supply - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a power supply, and more particularly to a power supply applicable to an image forming apparatus such as a copying machine or a printer.

BACKGROUND OF THE INVENTION Conventionally, a power supply device for a copying machine has been configured such that a low-voltage power supply for sequence control, a power supply for exposure, and a high-voltage power supply for charging are respectively independent power supplies.

The charging high-voltage power supply is configured to boost the stabilized low-voltage power supply output (generally 24 V) to 5 to 9 KV by a DC-DC inverter. Such a conventional device has many drawbacks in that it requires a large number of transformers and drive circuits and reduces power efficiency.

From such a viewpoint, attempts have been made to integrate the low-voltage power supply and the high-voltage power supply. However, when the transformer is integrated, it is difficult to control the high voltage according to the sequence signal because a high voltage output is generated at the same time when the power is turned on.

[Purpose] The present invention has been made in view of the above points, and it is an object of the present invention to provide a power supply device that realizes downsizing, low cost, high efficiency, and further enhances reliability. is there.

Embodiment An embodiment of the present invention will be described below in detail with reference to the drawings. In one embodiment of Figure 1 the present invention, 1 is a driving circuit of the power supply for the converter transformer T ₁ of the when to quenching transistor T _r1, 2 is Regiyureta circuit of the sequence control power source (typically 24V).

Converter transformer T ₁ is L _1, L ₁ in Giyatsupu 3-1 'low voltage winding section of the L _2, L _2', is separated into high-voltage winding of the L ₂ ".
L ₂ ′ is a high voltage winding, a high voltage diode D ₁ and a high voltage capacitor.
Pressure is output to the high-voltage terminal P ₅ is rectified and smoothed by C _1.

Now, it is energized when power is supplied to the primary winding L _1.
L ₁ ′ is tightly coupled to L ₁ and wound, so approximately 26
An output of ~ 29V RMS is obtained, rectified by D2, stabilized to 24V by the regulator circuit 2, and then supplied to the sequence control circuit via output terminals P3, P4. In this case, S1 is therefore remains open L _2, L ₂ ', the magnetic flux of L ₂ "magnetic core the windings is wound in, .L ₂ is sufficiently attenuated by Giyatsupu 3-1,
The L ₂ ′, L ₂ ″ windings are tightly coupled as shown in FIG.
₂ 'windings are high-voltage winding, L ₂ "winding is a control winding of the high pressure. At a time of non-copying, T _r2 are to L ₂ winding so rendered conductive by the control signal to the P6 induced voltage high-voltage output becomes very small, less than or equal to 1 KV. the time of copying work is the sequence control circuit, switch S1 is turned on. become simultaneously T _r2 is opened, L by energizing the L ₂ winding
_A predetermined high voltage is induced in the ₂ 'winding, and a DC high voltage necessary for image formation is supplied to the charger via a terminal P5.

In Figure 2 shows a structural diagram of the actual winding of the transformer T _1. The gap 3-1 shown in FIG. 1 is actually composed of the A, B and C gaps. The gap in section C is set sufficiently small with respect to sections A and B to reduce the voltage induced in the L ₂ ′ winding when S1 is cut off.

 FIG. 5 shows the details of the transformer drive circuit of the present invention.

The power supply side of the primary windings L ₁ and L ₂ is commonly connected to a rectified and smoothed output of a line input. The other end is connected to the respective scan Germany quenching transistor T _r 21T _r 22. The energization ratio of each transistor is controlled by PWM circuits 21 and 22. Secondary winding
The output of L ₁ ′ is stabilized at 5 V and supplied to the sequence control circuit. The signal is divided at a predetermined ratio by R ₂₁ and R ₂₂ and compared with the output of the constant voltage element 29 by the error amplifier 27. The comparison output is isolated by the photocoupler 26,
It is input to the PWM circuit 21 to stabilize + 5V.

The output of the secondary winding L ₂ ′ is fed to the charger, the load current of which is detected at R ₂₃ and compared with the sequence control voltage connected to terminal 21 by the error amplifier 28.

The comparison output is isolated by the photocoupler 25 and input to the PWM circuit to stabilize the load current of the charger connected to P5.

FIG. 3 shows an example in which the high-voltage output is controlled only by the high-voltage control winding L ₂ ″ with only the primary winding L ₁ .

Also in Figure 3 detects the load current of the charger in the resistor R _4, the collector current or the high voltage control winding L ₂ in addition to the base of the T _r2 is compared with a reference value at the error amplifier 4 T _r2 " 5 is an analog switch circuit that conducts _Tr2 during non-copying by a control input to P6, and the charging current flowing through R4 during copying is a predetermined value by a control input to P6. The reference voltage is switched so that

Figure 4 is, in the embodiment of Figure 3, in which the T _r2 by adding the output of the error amplifier 4 to the PWM circuit 7 was up-efficiency and switching-controlled.

In the embodiment shown in FIG. 5, a plurality of switching transistors and a plurality of PWM circuits for driving the switching transistors are provided by using a common power source for the primary winding. However, in the embodiment shown in FIG. the high-pressure side in common with the T _r 21 to delete when to quenching transistor T _r 22, it is also possible to connect to the variable power supply output, such as the other end of the L ₂ series the regulation Yu chelator or when to quenching the regulation Yu regulator .

In addition, regarding the embodiment of FIG. 5, the switching transistors of the primary windings L ₁ and L ₂ are made common, and are directly driven by the output of the oscillation circuit without passing through the PWM circuit. A control method using a regulator, a switching regulator, or the like is also possible.

As is clear from the above embodiment, the low-voltage power supply and the high-voltage power supply can be supplied from the same transformer, and the timing of the high-voltage output can be controlled by a sequence signal.

In the third and fourth embodiments, the switching of the primary side power supply can be omitted, so that it becomes simpler.

Further, as shown in Embodiments 3 and 4, stabilization control of the high voltage output becomes possible.

In the embodiment shown in FIGS. 5 and 6, not using a mechanical switch such as a relay or the like, it is possible to control not only on / off control but also continuous output independently.

[Effects] As described above, according to the present invention, high-voltage and low-voltage power can be supplied from the same transformer, and can be controlled independently of each other. Since the degree of coupling can be reduced, the induced voltage on the secondary winding of the high-voltage power supply due to the influence of the winding of the low-voltage power supply when the switching means for the high-voltage power supply is cut off can be reduced. Therefore, the reliability can be improved as well as miniaturization, low cost, and high efficiency.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a power supply device according to one embodiment of the present invention, and FIG. 2 is a converter transformer T ₁ used in the embodiment of FIG.
FIG. 3 is a circuit diagram of a power supply device according to another embodiment of the present invention, FIG. 4 is a circuit diagram of a power supply device according to still another embodiment, and FIGS. 5 and 6 are drive circuits. FIG. 1 ... Switching transistor drive circuit 2 ... Regulator 4 ... Error amplifier 7 ... PWM circuit T ₁ ... Converter transformer

Claims (1)

(57) [Claims] 1. A power supply device for extracting high-voltage and low-voltage power from a plurality of secondary windings of the same converter transformer, wherein a magnetic core of the transformer is divided into a plurality of parts by a gap, and a magnetic core at one of the divided ends is provided. A pair of a primary winding and a secondary winding for a low-voltage power supply that are tightly coupled to each other is provided, and a primary winding and a secondary winding for a high-voltage power supply that are tightly coupled to each other are provided on the magnetic core at the other end. Provide a pair of windings, make the gap of the magnetic core between each pair of windings smaller than the gap of the core at the end, and connect a separate switching circuit to the primary side of each pair of windings A power supply device characterized in that: