JPH0578165B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power supply device, and particularly to a power supply device effective for application to electronic image forming apparatuses that require a low-voltage power source and a high-voltage power source, such as electronic copying machines and electronic printers. It is.

Conventionally, in this type of electronic image forming apparatus,
Sequence-controlled low-voltage power supplies first convert commercial AC power to low-voltage DC through a low-voltage transformer and rectifier circuit, then use sequence control circuits, lamps,
At the same time as being supplied to a solenoid or the like, the DC output was supplied to the primary side of a high voltage transformer of a high voltage power supply for powering a charger via an inverter circuit. For this reason, the high-voltage output is multiplied by the conversion efficiency of the low-voltage power supply and the high-voltage power supply, resulting in a significant drop in energy efficiency.Also, the drive circuits for the low-voltage and high-voltage transformers are doubled, which increases the number of parts. This, in turn, led to an increase in the size of the equipment and cost.

The present invention was proposed in view of the above, and an object of the present invention is to improve the power conversion efficiency and obtain a small, highly reliable power supply device with a small number of parts. Also,
SUMMARY OF THE INVENTION An object of the present invention is to achieve a compact size through high-density packaging, suppress temperature rise, and prevent failure of heat-generating circuit elements.

FIG. 1 is a circuit diagram showing an embodiment of the present invention, in which 1 is a commercial AC power supply connected to the input side of the rectifier circuit 2, and 3 is a low voltage inverter transformer 4 connected to the output side of the rectifier circuit 2. Control circuits W1 to W3 for drive control are secondary windings of the low voltage inverter transformer 4.

The control circuit 3 includes a switching transistor oscillation circuit, a PWM (pulse width modulation) circuit, an error amplifier, etc., and compares the rectified output of the rectifier circuit 7 which receives the output of the secondary winding W3 with a reference value. The energization time of the low voltage inverter transformer 4 is controlled so that the rectified output is constant.

The rectified output of the rectifier circuit 6 which receives the output of the secondary winding W2 as input is outputted to terminals 12 and 13, and is approximately 2
A voltage of around 4V is supplied to low voltage circuits such as a sequence control circuit, a lamp, and a solenoid (not shown) connected to the terminal.

The secondary winding W1 is connected to one of the high voltage inverter transformers 8 via an electrical or mechanical switch 5.
Connected to the next winding. The rectified output of the rectifier circuit 9 connected to the secondary side of the high voltage inverter transformer 8 is maintained at a constant voltage by the constant voltage characteristics of the control circuit 3 and the high voltage inverter transformer itself.
This constant voltage is supplied to a high voltage circuit such as a charger (not shown) connected to the terminals 10 and 11.

In this embodiment, a relay is used as the switch 5, which is opened and closed in response to a sequence control signal. By turning on and off this switch, the power supply to the high voltage circuit can be turned on and off independently from the low voltage circuit, and since the power supply to the high voltage circuit can be turned on and off in the low voltage state, the withstand voltage of the switch itself can be reduced. .

FIG. 2 is an external perspective view of an embodiment of the present invention, and FIG. 3 is a longitudinal sectional view thereof. In FIGS. 2 and 3, insulating cylinders 15 and 16 are erected on the surface of the substrate 14.
A bobbin 18 on which the primary coil 17 of the low-voltage inverter transformer 4 is wound is fitted into one of the cylindrical bodies 15, and the secondary coils W1 and W are placed on the outside of the bobbin.
2, a bobbin 20 wound with W3 is fitted. Further, a bobbin 22 on which a primary coil 21 of a high-voltage inverter transformer 8 is wound is fitted into the other cylinder 16, and a bobbin 24 on which a secondary coil 23 is wound on the outside of the bobbin. There is. Lead terminals 4a and 8a of the transformers 4 and 8 are provided protruding from the back surface of the substrate 14. Rectifiers 9a to 9d constituting the high voltage rectifier circuit 9 are connected to the secondary coil 23 of the high voltage inverter transformer.

19 is a hole 25 into which the cylinders 15 and 16 are fitted;
26 and a partition recess 27 for partitioning between the bobbins 18, 20 of the low-voltage inverter transformer 4 and the bobbins 22, 24 of the high-voltage inverter transformer 8 and increasing insulation against alternating current components, as shown in FIG. As shown, cover each bobbin, rectifier, and other circuit elements connected to each of the above coils, such as switching transistors, electrolytic capacitors, etc.
An epoxy-based highly insulating and highly thermally conductive resin 28 is vacuum injected and dried and integrated. Reference numerals 29 and 30 indicate iron cores inserted into the cylindrical bodies 15 and 16.

Figure 4 shows a heat sink 31 on the outside of the case 19.
This is an example in which the screws are attached with screws 32. In the case of this example, as shown in FIG. 5, the fin portion 33a of the switching transistor 33 (another element that generates a large amount of heat, such as an electrolytic capacitor may be used) is attached to the inner surface of the wall surface of the case 19 that is in close contact with the heat sink 31. The switching transistor 33 is connected to the heat sink 31 with very low thermal resistance by holding the fin portion 33a in contact with the heat sink 31 by a holding plate 34 provided on the inner surface of the case. Therefore, the heat generated by the switching transistor 33 is efficiently dissipated.
It is possible to improve reliability by eliminating failures caused by heat.

As detailed above, the present invention connects the secondary winding of the low-voltage inverter transformer and the primary winding of the high-voltage inverter transformer, so there is no need for any drive circuit on the primary side of the high-voltage inverter transformer. Therefore, switching and other losses in the drive circuit can be eliminated and power conversion can be made highly efficient. Further, there is no noise caused by switching, heat generation due to switching loss, etc., and the number of parts is reduced, so reliability can be significantly improved, and miniaturization and cost reduction can be achieved.

In addition, a low-voltage inverter transformer and a high-voltage inverter transformer are housed in the same case, and the circuit elements connected to the transformer are brought into contact with the inner surface of the case, and a highly insulating and highly thermally conductive resin is injected into the interior of the case. Since it is filled and integrated as a whole, each component can be brought close to each other by shortening the insulation distance stipulated by the safety regulations, and can be densely mounted, making it possible to significantly downsize the power supply device. Further, since the case and the filled resin have high thermal conductivity, the heat of the circuit elements can be efficiently dissipated, and failures of the circuit elements can be prevented.

Note that the high-voltage inverter transformer 8 may have a plurality of secondary windings to supply power to a plurality of chargers having different charging voltages.

In the above embodiment, the control circuit 3 is composed of a switching transistor oscillation circuit, a PWM circuit, and an error amplifier, implying that it is a separately excited inverter. By adding a feedback winding, it is possible to simplify the self-excited inverter by removing the oscillation circuit.

The stabilizing output of low voltage inverter transformer 4 is set to 2.
It is also possible to use the rectified output of the secondary winding W2 instead of the rectified output of the secondary winding W3. Therefore, the secondary winding W1
It is also possible to easily stabilize the output of the high voltage inverter transformer 8 or the output of the high voltage inverter transformer 8 itself.

In addition to the rectifiers 9a to 9d that make up the high-voltage rectifier circuit 9, case 1 also includes circuit components that share a ground with the input commercial power source, which is called a primary circuit due to safety standards.
By housing the device in the 9 and integrating it with a filled high insulating material, the insulation distance can be shortened and the device can be made more compact.

In the illustrated example, the primary coil and secondary coil of the low-voltage inverter transformer 4 are wound on separate bobbins 18 and 20, but they may be wound on the same bobbin.

In addition, in the illustrated example, the shield plate that covers the case 19 from the front is used as a heat sink in order to shield unnecessary radiation noise from the coil of the high-voltage inverter transformer 8. A shield plate or heat sink may be provided only on the exposed surface. This heat sink may also be used as the power supply unit case or the frame of the main body.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of the power supply device of the present invention, Fig. 2 is an external perspective view of the power supply device of the present invention, Fig. 3 is a vertical sectional view thereof, Fig. 4 is a side view with a heat sink attached, and Fig. 5 is its external perspective view. It is a sectional view of the main part. 4 is a low voltage inverter transformer, 8 is a high voltage inverter transformer, 19 is a case, 28 is a highly insulating and highly thermally conductive resin, 31 is a heat sink, and 33 is a switching transistor.

Claims (1)

[Claims] 1. A first transformer that has a primary winding and a plurality of secondary windings that are supplied with power from a power source and supplies a low voltage output to a low voltage circuit, and is connected to one of the secondary windings of the first transformer. a second transformer having a primary winding that supplies a high voltage output to a high voltage circuit; and a second transformer that is connected between a secondary winding of the first transformer and a primary winding of the second transformer. A power supply device characterized by comprising a switch that turns on and off a high voltage circuit.