JPH0510519Y2 - - Google Patents

Description

[Detailed Description of the Invention] "Industrial Application Field" The present invention relates to an AC high-voltage power supply in which direct current is superimposed on alternating current, which is used to apply power to various corotrons of copying machines, for example.

``Prior Art'' In an electronic copying machine, a photoreceptor is uniformly charged using a charger, and then exposed to light to form an electrostatic latent image. This electrostatic latent image is developed by a developing device to create a toner image. The toner image is transferred onto paper by a transfer device. After the toner image has been transferred, the photoreceptor is neutralized by a static eliminator and cleaned by a cleaning device.

In such a basic copying process, high AC voltage is applied to a static eliminator from an AC high voltage power supply. In some devices, a corotron called a detack corotron is used to transfer a toner image, and a high alternating current voltage is also applied to this corotron.

By the way, in the normal case, an AC high voltage power supply is attached to an overcurrent detection circuit, so that when some kind of accident occurs, the generation of high voltage is immediately stopped. The overcurrent detection circuit rectifies and divides the voltage on the output side of the AC high voltage power supply and compares it with a reference voltage to check whether an overcurrent has occurred.

FIG. 3 shows a conventionally proposed AC high voltage power supply equipped with an overcurrent detection circuit. A high voltage generation circuit 1 surrounded by a broken line in this power supply is constituted by a kind of switching regulator, which alternately switches two transistors 2 and 3 to generate high voltage on the secondary side of a transformer 4. . A capacitor 5 provided on the secondary side of the transformer 4 is a filter capacitor for adjusting the output waveform. The high alternating voltage generated in this way is
It is also input to the overcurrent detection circuit 7 surrounded by a broken line.

The overcurrent detection circuit 7 includes a half-wave voltage doubler circuit 8 and a comparator 9 for voltage comparison. The half-wave voltage doubler circuit 8 rectifies the AC voltage generated across the detection resistor R ₁ with a half-wave voltage doubler circuit consisting of rectifiers CR ₁ , CR ₂ and capacitors C ₁ , C ₂ .
Generates a DC voltage proportional to the output voltage across resistor _R2 . This DC voltage is taken out at a predetermined voltage division ratio and compared with a reference voltage 11 by a comparator 9. When a voltage exceeding this reference voltage is input from the half-wave voltage doubler circuit 8, an overcurrent detection signal 12 is output from the comparator 9.
High voltage generating circuit 1 immediately stops its output.

In an AC high voltage power supply with such a configuration, this third
As shown in the figure, it is convenient to use a half-wave voltage doubler circuit for the overcurrent detection circuit 7. The reason for this is as follows.

Simply performing half-wave rectification makes it impossible to detect both overcurrent on the positive side and overcurrent on the negative side of AC. Therefore, half-wave rectifier circuits are not preferred.

As shown in FIG. 4, when a full-wave bridge circuit 14 is used in the overcurrent detection circuit 7, the low voltage side of the detection resistor _R1 and the resistor _R2 on the output side of the bridge circuit is have to be commonly connected. However, when these are connected in common, full-wave rectification is no longer possible, and half-wave rectification is required.

``Problems that the invention seeks to solve'' By the way, in some types of corotron copying machines, DC voltage is superimposed (offset) on AC voltage to enhance the effectiveness of static elimination, etc. Since the AC high voltage power supply for this purpose includes both an AC power supply section and a DC power supply section, it is necessary to detect overcurrent in each of these sections. However, in the half-wave voltage doubler circuit 8 shown in FIG. 3, even if an abnormality occurs in the DC voltage, it cannot be stably detected. This is because the detected voltage of the half-wave voltage doubler circuit 8 is divided by the leakage current ratio of the capacitors C ₁ and C ₂ , so its value cannot be specified.

Therefore, an object of the present invention is to provide an AC high-voltage power supply that can reliably detect not only abnormalities in the AC power supply section but also abnormalities in the DC power supply section.

``Means for solving the problem'' This invention consists of a high voltage generation circuit that generates an AC high voltage, and a DC circuit that superimposes a DC component on this high voltage.
An offset circuit, a half-wave voltage doubler circuit that performs half-wave voltage doubler rectification of the output that has passed through this DC offset circuit, and the output of this half-wave voltage doubler circuit is compared with a reference value to calculate both AC and DC components. In an AC high-voltage power supply equipped with an overcurrent detection section that detects the occurrence of overcurrent, a resistor is connected in parallel with the capacitor that constitutes the half-wave voltage doubler circuit, and when a DC overcurrent occurs, this path is A current is actively applied to generate a voltage corresponding to the overcurrent on the output side of this circuit.

"Example" The present invention will be described in detail with reference to Examples below.

FIG. 1 shows an AC high voltage power supply in one embodiment of the present invention. Components that are the same as those in FIG. 3 are designated by the same reference numerals, and their descriptions will be omitted as appropriate.

In this AC high-voltage power supply, a DC offset circuit 21 is connected to the output side of the high-voltage generating circuit 1, and a DC voltage of, for example, about 1000 volts is superimposed thereon. The DC offset circuit 21 of this embodiment includes a power supply section 23 connected to the primary side of the transformer 22, a rectifier CR connected to the secondary side of the transformer 22, and a CR coupling circuit 24 consisting of a capacitor C and a resistor R. It consists of AC by DC offset circuit 21
The superimposed output voltage of DC and DC is applied to a corotron (not shown) through a terminal 26, and is also supplied to an overcurrent detection circuit 27. The overcurrent detection circuit 27 includes a half-wave voltage doubler circuit 28 and a comparator 9. The half-wave voltage doubler circuit 28 is constructed by connecting a DC balance resistor _R3 in parallel to the capacitor _C1 of the half-wave voltage doubler circuit 8 shown in FIG.

In an AC high voltage power supply having such a configuration, if the terminal 29 connecting the high voltage generation circuit 1 and the DC offset circuit 21 is grounded for some reason, or if the DC offset circuit 21 itself goes out of control, a DC overcurrent i will occur. I will do it. This overcurrent i is
In addition to flowing through the detection resistor _R1 , the current flows through the DC balance resistor _R3 and the resistor _R2 via the rectifier _CR2 . Therefore, when a DC overcurrent i occurs, a relatively large voltage is generated across the resistor _R2 depending on the voltage.
It will be applied to the comparison input terminal of comparator 9. When the potential at the connection point between the resistor R ₂ and the rectifier CR ₂ is input to this comparison input terminal, a voltage V approximately as shown below will be generated.

V=R ₁・R ₂・i/R ₁ +R ₂ +R ₃ In other words, when an overcurrent i occurs, this voltage V is compared with a lower reference voltage 11 and an overcurrent detection signal 12 is generated. .

On the other hand, when an abnormal AC voltage occurs, a relatively high voltage is generated at the resistor R ₂ in the half-wave voltage doubler circuit 28 through the same circuit operation as shown in FIG.
Similarly, an overcurrent detection signal 12 is generated from the comparator 9.

FIG. 2 shows a portion of an overcurrent detection circuit for DC offset circuits having different polarities as a modified example of the present invention. In the case of this overcurrent detection circuit 31, the anodes and diodes of the rectifiers CR ₁ and CR ₂ are connected in the opposite direction to those in FIG. 1. The comparison operation of comparator 9 is the first
This is similar to the example shown in the figure. Note that the comparison input voltage of the comparator 9 shown in FIGS. 1 and 2 can be adjusted by appropriately dividing the output voltage of the resistor _R2 .

"Effects of the Invention" As explained above, according to the present invention, since a half-wave voltage doubler circuit is used, both positive and negative overcurrents of alternating current can be detected. Moreover, since a resistor for DC balance is added to this half-wave voltage doubler circuit, there is an effect that abnormal DC voltage can be detected with high reliability.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of an AC high voltage power supply according to an embodiment of the present invention, Fig. 2 is a circuit diagram of an overcurrent detection circuit portion for explaining a variation of the present invention, and Fig. 3 is a circuit diagram of an overcurrent detection circuit portion used conventionally. FIG. 4 is a circuit diagram showing an example of an AC high voltage power supply, and FIG. 4 is a circuit diagram showing an example in which a bridge circuit is used as an overcurrent detection circuit. 1... High voltage generation circuit, 21... DC offset circuit, 27... Overcurrent detection circuit, 28, 31...
Half-wave voltage doubler circuit, _R3 ...DC balance resistor.

Claims (1)

[Claims for Utility Model Registration] A high-voltage generation circuit that generates an AC high voltage, a DC offset circuit that superimposes a DC component on this high voltage, and a half-wave voltage doubler rectifier that performs half-wave doubler rectification of the output that has passed through this DC offset circuit. a voltage doubler circuit; and an overcurrent occurrence detection section that compares the output of the half-wave voltage doubler circuit with a fixed value serving as a reference to detect the occurrence of overcurrents in both AC and DC components; The voltage doubler circuit includes a first detection resistor _R1 that generates an output voltage at both ends thereof in accordance with the output that has passed through the DC offset circuit, and a rectifier _CR1 and a capacitor _C1 connected in parallel to the detection resistor _R1 . a second series circuit consisting of a rectifier CR ₂ and a capacitor C ₂ connected in parallel with and in the opposite direction to the rectifier CR ₁ ; and a second series circuit on the output side connected in parallel with the capacitor C ₂ . A resistor R ₂ and a DC balance resistor connected in parallel with the capacitor C ₁
An AC high voltage power supply characterized by comprising _R3 .