JPH04237986A - Ac high-voltage generating circuit - Google Patents

Abstract

PURPOSE:To use a high-voltage transformer at a high frequency and miniaturize it at a low cost. CONSTITUTION:Low-pass filters 109-113 for smoothing the high voltage on the output side of a high-voltage transformer 108 converting the low voltage to the high voltage and amplitude modulating means 101-105 amplitude- modulating the second frequency which can not pass the low-pass filters 109-113 with the first frequency which can pass the low-pass filters 109-113 are provided, and the modulated voltage generated by this amplitude modulation is applied to a coil on the input side of the high-voltage transformer 108.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-voltage AC voltage generating circuit suitable as a power supply means for a charging means incorporated in an image forming apparatus such as an electrophotographic copying machine.

0002

2. Description of the Related Art For convenience, a copying machine or a printer using a transfer type electrophotographic process shown in FIG. 5 will be described as an example.

Reference numeral 219 denotes a rotating drum-type electrophotographic photoreceptor (hereinafter referred to as a photoreceptor drum) as an image carrier, and a photoreceptor layer (photoconductor layer) is formed on the outer peripheral surface of a conductive drum base made of aluminum or the like. is formed and is rotated clockwise as indicated by the arrow at a predetermined circumferential speed (process speed).

During the rotation process of the photosensitive drum 219, the outer circumferential surface of the photosensitive drum 219 is sequentially subjected to a uniform charging process of a predetermined polarity and potential by a charging unit 218, an exposure process L by an image information exposure unit (not shown), and a development process by a developing unit 221. Then, a transferable image (toner image) corresponding to the target image information is formed.

The transferable image formed on the photosensitive drum surface is transferred between the photosensitive drum 219 and a transfer roller 22 as a transfer means.
0, the image is sequentially transferred onto the surface of a recording material P fed at a predetermined timing from a paper feeding means (not shown), and the recording material that has undergone the image transfer is transferred via an image fixing means (not shown). It is output as an image formed product (copy, print). After the image has been transferred, the surface of the photosensitive drum 219 is cleaned by cleaning means 225 to remove contaminants such as residual developer after transfer, and is used repeatedly for image formation.

In this example, the charging means 218 is a contact charging type charging device using a charging roller. Charging roller 2
18 is basically composed of a conductive core metal and a conductive elastic layer formed concentrically with the core metal into a roller shape by molding, etc., and is pressed against one surface of the photosensitive drum with a predetermined pressing force. In this example, the photosensitive drum 1 rotates as the photosensitive drum 1 rotates. A predetermined voltage is applied to the charging roller 218 by a power supply circuit (high voltage power supply), so that the surface of the rotating photosensitive drum is charged to a predetermined polarity and potential by a contact charging method.

In order to uniformly charge the surface of a charged object such as a photosensitive drum by a contact charging member such as a charging roller, a voltage that is a combination of a predetermined DC voltage and a predetermined AC voltage is applied to the contact charging member such as the charging roller. It is effective to carry out the charging process using
No. 33, etc.).

In this example as well, a superimposed voltage of DC and AC, which is the sum of the DC high voltage power supply 217 and the AC voltage output from the high voltage transformer 211, is applied to the charging roller 218 as a contact charging member to charge the photoconductor surface. It is designed to charge uniformly. At this time, an equivalent circuit between the charging roller 218 and the photoreceptor is a circuit shown by resistors 222 and 224 and a capacitor 223, and the voltage across the capacitor 223 becomes the charging voltage of the photoreceptor.

As the frequency of the high-voltage AC voltage increases, the AC current increases due to the capacitor 223, resulting in a large load. Further, the photoreceptor cannot be uniformly charged only with a high DC voltage. If the frequency of the high-voltage AC voltage is selected under such conditions, a frequency of 1.5 KHz or less will be appropriate. However, at a frequency of 1 to 1.5 KHz, vibrations of the shaft of the charging roller generate a very unpleasant sound called charging noise. To solve this problem, the frequency is made very low to about 150Hz. In FIG. 5, the pulse generator 201 oscillates this 150 Hz pulse. The pulse waveform output from the pulse generator 201 is generated by a resistor 202, a resistor 203, and an operational amplifier 205.
The peak voltage is determined by the output voltage of and approximated to a sine wave by the resistor 227 and capacitor 225. The operational amplifier 209 is a portage follower and applies an approximated sine wave voltage to the low voltage side coil of the high voltage transformer 211 through the capacitor 210.

[0010] The resistor 216 and the capacitor 215 detect the high voltage AC component current as the voltage across the resistor 216. The voltage across the resistor 216 is the capacitor 214
It passes through diodes 212 and 213 and is rectified, and is detected as a DC voltage by resistors 208 and 206 and a capacitor 226.

This voltage is applied to the resistor 2 based on the reference voltage 207.
The output voltage of the operational amplifier 205 is amplified by the gain determined by 04 and 228. However, as described above, the peak voltage output from the pulse generator 201 is controlled by the high voltage AC component current. In other words, as the current of the high-voltage AC component increases, the peak voltage of the pulse decreases, and as a result, the peak-to-peak voltage value of the high-voltage AC voltage decreases.

In the above circuit, the pulse generator 201 is a low frequency generating means. Capacitor 215/Resistor 21
Reference numeral 6 constitutes an alternating current detecting means for detecting an alternating current flowing from the charging roller 218, which is a load, to the photoreceptor 219. Circuit elements 202-208, 212-214, 225
228 constitute a peak voltage control means for controlling the peak voltage of the low frequency generation means 201 based on the information from the alternating current detection means 215 and 216.

[0013]

[Problems to be Solved by the Invention] In the above conventional example, the high voltage transformer 211 is used at a very low frequency of 150 Hz, so the high voltage transformer 211 becomes very large, and it is difficult to miniaturize the device. was becoming a huge problem. Furthermore, the cost of the transformer was also extremely high.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to enable a high voltage transformer to be used at a high frequency in a high voltage AC generating circuit, thereby making it possible to reduce the size and cost of the high voltage transformer.

[0015]

[Means for Solving the Problems] The present invention provides a low-pass filter for smoothing a high-voltage voltage on the output side of a high-voltage transformer that converts a low-voltage voltage into a high-voltage voltage, and a first frequency that can pass through the low-pass filter. A high-voltage device comprising an amplitude modulation means for amplitude-modulating a second frequency that cannot pass through the low-pass filter, and applying a modulated voltage created by the amplitude modulation to a coil on the input side of the high-voltage transformer. It is an AC voltage generation circuit.

[0016] Furthermore, in the above, the high voltage AC voltage generation circuit is characterized in that the degree of modulation in the amplitude modulation means is varied depending on the value of the AC current generated by the high voltage AC voltage that is the output of the low pass filter.

[0017]

[Operation] With such a circuit configuration, the high voltage transformer can be used at a high frequency, and the high voltage transformer can be made smaller and lower in cost. That is, in general, if the cross-sectional area of the transformer core is S, and the range of change in magnetic flux density is ΔB, then
The following formula holds true.

(S・ΔB)=(Ein・Ton)/Np
Ton: ON time Np: Primary winding Ton is ON. If the duty is Don, then Ton=Don/
f (f is switching frequency) (S・Np・ΔB
)=(Ein・Ton)/f, and the metamorphic shape S・N
p and the switching frequency f are inversely proportional. That is, if losses are ignored, the higher the switching frequency f is, the smaller the transformer can be.

[0019]

[Embodiment] <First Embodiment> (FIGS. 1, 2, and 3) FIG. 1 shows an embodiment of the present invention. Same parts as the conventional example shown in Figure 5 above.
The members are given the same reference numerals as in FIG. 5 (numbers in the 200s), and repeated explanations will be omitted.

The circuit of this example includes low-pass filters 109 to 113 for smoothing the high voltage on the output side of a high-voltage transformer 108 that converts a low voltage to a high voltage, and a first frequency that can pass through the low-pass filter. It has amplitude modulation means 101 to 105 that amplitude modulates a second frequency that cannot pass through a low-pass filter, and is configured to apply a modulated voltage created by this amplitude modulation to the coil on the input side of the high voltage transformer 108. It is.

A waveform approximated to a sine wave similar to the conventional example is input to the non-inverting input of the operational amplifier 101. The output of the operational amplifier 101 operates the transistor 103 through the resistor 102. The Al electrolytic capacitor 105 is charged by the transistor 103. Discharging of capacitor 105 is performed by a high voltage load and diode 104. This allows capacitor 1
The voltage across 05 becomes a waveform voltage approximated to a sine wave. This voltage is applied to the high frequency pulse oscillator 106 and the power MOS
107, the voltage is applied to the low voltage side coil of the high voltage transformer 108 as shown in FIG.

A voltage boosted by the turns ratio of the high voltage transformer is also output to the high voltage output side coil of the high voltage transformer 108 as shown in FIG. This is a diode 109 and a resistor 110
・When smoothed by 111 and capacitors 112 and 113, the voltage shown in FIG. 3 is output across the capacitor 113. Below, as in the conventional example, the output peaks and
The peak voltage value is controlled.

In the above, the circuit elements 109 to 113 constitute a low-pass filter for smoothing the high voltage output from the high voltage transformer 108. circuit element 10
1 to 105 are peak voltage control means 202 to 208, 21
2 to 214 and 225 to 228 constitute a low voltage modulation means (amplitude modulation means) that modulates a DC low voltage based on the low frequency AC voltage created by 2 to 214 and 225 to 228. A high frequency pulse generator 106 is a high frequency generating means that generates a frequency that cannot pass through the low pass filters 109 to 113. A power MOS 107 is a switching means that applies the low voltage AC voltage modulated by the low voltage modulating means 101 to 105 to the low voltage side coil of the high voltage transformer 108 based on the frequency of the high frequency generating means 106.

That is, the high-voltage AC voltage generating circuit of this embodiment is as follows:
Low-pass filters 109 to 113 for smoothing the high voltage output from the high-voltage transformer 108, alternating current detection means 215 and 216 for detecting alternating current flowing from the charging roller 218 as a load to the photosensitive drum 219, and the low-pass filter 109 to 113; and peak voltage control means 2 to control the peak voltage of the low frequency generating means 201 based on information from the alternating current detecting means 215 and 216.
02 to 208, 212 to 214, 225 to 228, and low voltage modulation means 10 that modulates the DC low voltage based on the low frequency AC voltage created by the peak voltage control means.
1 to 105, and high frequency generating means 106 for generating frequencies that cannot pass through the low pass filters 109 to 113.
and a switching means 107 for applying the low-voltage AC voltage modulated by the low-voltage voltage modulating means to the low-voltage side coil of the high-voltage transformer 108 based on the frequency of the high-frequency generating means 106. The transformer 108 can be used at a high frequency, and the high voltage transformer can be made smaller and lower in cost.

<Second Embodiment> (FIG. 4) FIG. 4 shows another embodiment. The same parts and members as the conventional example shown in FIG. 5 and the first embodiment shown in FIG.
number and 100 series code) and omit further explanation.

The MPU 307 converts the high voltage alternating current detected as a direct current voltage by the resistors 208 and 206 and the capacitor 226 into digital information by an A/D converter 308. Based on that information, a low frequency sine wave is created and the A/
When the D conversion value becomes larger than the target value, Vp-p of the sine wave is decreased. A sine wave created as digital information is input as a voltage to a non-inverting input of an operational amplifier 302 by a D/A converter 306 . The operational amplifier 302 and the transistor 301 operate so that the voltage divided by the resistors 303 and 304 becomes equal to the voltage output from the D/A converter 306. However, capacitor 305
The voltage across is a sine wave. Transistor 30 above
1. The operational amplifier 302, resistors 303 and 304, and capacitor 305 are amplitude modulation means. Thereafter, the operation is similar to that of the first embodiment.

In the above embodiments, the first frequency has a waveform approximated to a sine wave, but it goes without saying that a rectangular wave is also possible.

[0028]

As described above, according to the present invention, it is possible to use a high voltage transformer at a high frequency in a high voltage alternating current generating circuit, and it is possible to downsize and reduce the cost of the high voltage transformer. It is effective and suitable as a power source for applying an alternating current component to a contact charging member.

[Brief explanation of the drawing]

[Figure 1] Circuit diagram of the first embodiment

[Figure 2] High voltage transformer applied voltage waveform

[Figure 3] Output high voltage AC voltage waveform

[Figure 4] Circuit diagram of the second embodiment

[Figure 5] Circuit diagram of conventional example

[Explanation of symbols]

218 Charging roller 219 as a contact charging member
Photosensitive drums 108 and 211 as charged objects High voltage transformer 217 DC high voltage power supply

Claims (2)

[Claims] 1. A low-pass filter for smoothing a high-voltage voltage on the output side of a high-voltage transformer that converts a low-voltage voltage into a high-voltage voltage, and a first frequency that can pass the low-pass filter and a first frequency that cannot pass the low-pass filter. A high-voltage alternating current voltage generating circuit, comprising an amplitude modulating means for amplitude-modulating a second frequency, and applying a modulated voltage created by the amplitude modulation to a coil on the input side of the high-voltage transformer. 2. The high-voltage alternating current voltage generating circuit according to claim 1, wherein the degree of modulation in the amplitude modulating means is varied depending on the value of alternating current generated by the high-voltage alternating voltage that is the output of the low-pass filter.