JP2002162870A - Image forming device and power source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power source device which has a good package efficiency of parts onto a printed wiring board, a reduced noise level, little fluctuation of output voltage, and is inexpensive. SOLUTION: An image forming device comprises a DC power source circuit provided with a converter transformer 303 and outputting a high voltage DC to a line 315, and at least one step-down power source circuit 320a for converting the DC output voltage value from the DC power source circuit by using a semiconductor element 325 and supplying it to the corresponding load.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus and a power supply, and more particularly, to an image forming apparatus having an image forming means for forming a toner image by using an electrostatic recording method, and an image forming apparatus and the like. The present invention relates to a high-voltage power supply used.

[0002]

2. Description of the Related Art First, an image forming operation of a laser beam printer will be described with reference to FIGS.

FIG. 9 is a diagram showing a configuration of a tandem type color image forming apparatus using an electrostatic recording system.

A tandem-type image forming apparatus uses a black (B
k) image, yellow (Y) image, magenta (M) image,
An image forming section for a cyan (C) image is provided for each color.

In each of the image forming sections, a photosensitive drum 18a to 18d, a primary charger 16a to 16d for uniformly charging the photosensitive drum 18a to 18d, and a latent image is formed on the photosensitive drum 18a to 18d. Scanner units 11a to 11d, developing units 14a to 14d for developing each latent image into a visible image, transfer units 19a to 19d for transferring each visible image to transfer paper, and residual toner on the photosensitive drums 18a to 18d Cleaning device 15a for removing each of
To 15d and the like are provided.

FIG. 10 is a diagram showing the structure of the scanner unit. Since the scanner units 11a to 11d have the same configuration, only one of them is shown.

Reference numeral 101 denotes an image signal (VDO signal).
The data is input to the laser unit 102 in the scanner unit 11. Reference numeral 103 denotes a laser beam that has been modulated on and off by the laser unit 102. 104, a scanner motor; a rotating polygon mirror (polygon mirror) 105;
Is rotated constantly. Reference numeral 106 denotes an imaging lens which focuses the laser beam 107 whose beam direction has been changed by the polygon mirror 105 on a surface to be scanned on the photosensitive drum 18.

Thus, the laser beam 103 modulated by the image signal 101 is horizontally scanned (scanned in the main scanning direction) on the photosensitive drum 18 to form a latent image on the photosensitive drum 18.

A beam detection port 109 receives a laser beam from a slit-shaped entrance. The laser beam entering from the entrance passes through the optical fiber 110 and is guided to the photoelectric conversion element 111. The laser beam converted into an electric signal by the photoelectric conversion element 111 is amplified by an amplifier circuit (not shown), and then becomes a horizontal synchronization signal.

Returning to FIG. 9, P is a transfer sheet made of a transfer material, and is supplied from a cassette 22. The fed transfer paper P is used to set the operation timing with each image forming unit.
The registration roller 21 waits for conveyance.

A first registration sensor 24 for detecting the leading end of the fed transfer paper P is provided near the upstream of the registration roller 21. The image forming control unit that controls each image forming unit estimates the timing at which the leading end of the transfer paper P reaches the registration roller 21 based on the detection result of the first registration sensor 24, and determines the first color (the yellow color in the example in the figure). Is formed on the photosensitive drum 18a as an image carrier, and the temperature of a heater (not shown) of the fixing device 23 is controlled to a predetermined temperature.

Reference numeral 29 denotes an attraction roller, which applies an attraction bias to the axis of the attraction roller 29 to electrostatically attract the transfer paper P onto the transport belt 20.

Transfer paper P waiting at registration roller 21
Measures the transport timing based on the detection result of the first registration sensor 24 and the timing of the first color image forming process,
While being transported on the transport belt 20 arranged to penetrate each color image forming unit, the first color image is transferred onto the transfer paper P by the transfer unit 19a.

Similarly, the transfer timing of the image of the second color (magenta in the example in the drawing) is measured based on the detection result of the second registration sensor 25 and the timing of the second color image forming process, and the image is transferred on the conveyor belt 20. The image is superimposed and transferred on the image of the first color on the transferred transfer paper P. Similarly, the image of the third color (cyan in the example in the figure) is based on the detection result of the third registration sensor 26, and the image of the fourth color (black in the example in the figure) is based on the detection result of the fourth registration sensor 27. Are sequentially superimposed and transferred onto the transfer paper P at the timing of each image forming process.

The transfer paper P to which the four color toner images have been transferred is
The sheet is fused and fixed by a fixing device 23 having a built-in halogen heater, and is discharged outside the apparatus.

Next, a conventional developing bias circuit used in each image forming section will be described with reference to FIGS.

FIG. 11 is a view showing the arrangement of each high-voltage bias circuit used in each image forming section (the above-mentioned suction bias is omitted).

Primary chargers 16a-16 of each image forming section
d, at least three types of high voltage of a charging bias, a transfer bias, and a developing bias (HV1 to HV4) are applied to the developing rollers 17a to 17d in the transfer units 19a to 19d and the developing units 14a to 14d, respectively.
To 30d, 31a to 31d, and 32a to 32d.

In an image forming apparatus having a tandem configuration, since four image forming units are provided, when different voltages are required in each image forming unit, twelve (= 3 × 4) high voltage bias circuits are required. Is required, the circuit scale of the high voltage bias circuit as a whole becomes large, and its cost also becomes high.

Therefore, in the developing bias circuit of the high-voltage bias circuit, as shown in FIG. 12, four high-voltage DC voltages HV1 to HV4 are individually divided based on the secondary-side pulse voltage obtained from one converter transformer 203. And the high-voltage contacts 221a to 221 of the developing units 14a to 14d.
A circuit system for outputting to 1d may be employed.

FIG. 12 is a circuit diagram showing a configuration of a conventional developing bias circuit comprising one converter transformer.

In the figure, S41 is a converter transformer 203.
Is a pulse wave for switching driving, for example, a rectangular wave fixed to 50 kHz, 25% on duty, and 5 V amplitude is used. When the square wave S41 is input to the base of the transistor 202, the transistor 202
Repeats on / off according to the rectangular wave S41. By turning on / off the transistor 202, the DC voltage across the electrolytic capacitor 201 is changed by the converter transformer 2
03 is applied as a switched pulse-like waveform to the primary winding. As a result, a boosted pulse-like voltage having the same cycle is output from the secondary side of the converter transformer 203.

The pulse voltage output to the secondary side is supplied to the capacitors C205, C206, C209 and the diode 2
The high-voltage DC voltage appears at both ends of the capacitor 209.

The secondary side rectifier circuit employs a voltage doubler rectifier circuit system that outputs a negative high voltage. And converter transformer 20
3, which outputs a DC voltage that is twice the voltage determined by the turns ratio or the like.

Next, a circuit portion for controlling the voltage across the capacitor 209 to a constant value will be described.

Reference numeral 210 denotes a voltage detecting resistor for detecting a voltage appearing at both ends of the capacitor 209, and a resistor having a high withstand voltage and a high accuracy of the resistance value (for example, tolerance of the resistance value ± 1%) is used. A voltage obtained by dividing the difference between the voltage between both ends of the capacitor 209 and the reference power supply voltage Vb by the resistors 210, 211, and 212 is input to the + input terminal of the operational amplifier OP-AMP214. The reference voltage Vc is input to the-input terminal of the OP-AMP 214.

Here, assuming that the resistors 210, 211 and 212 are R210, R211 and R212, respectively, and the voltage across the capacitor 209 is HV, the OP-AMP 214
In the operating state described above, the relationship represented by the following equation (1) holds between the reference voltage Vc, the voltage HV across the capacitor, and the reference power supply voltage Vb.

Vc = (HV · R211 · R212 + Vb · R210 · R212) / (R210 · R211 + R211 · R212 + R210 · R212) (1) The voltage input to the + input terminal of the OP-AMP 214 is −input. The base voltage of the transistor 204 is controlled to be equal to the reference voltage Vc connected to the terminal. That is, when the high-voltage output voltage HV (the voltage across the capacitor 209) becomes larger in the negative direction (absolute value becomes larger) than the value determined by the value of the reference voltage Vc, O
The positive input terminal voltage of the P-AMP 214 becomes smaller than the negative input terminal voltage. Therefore, the output of the OP-AMP 214 decreases and the transistor operates in a direction to turn off the transistor 204, so that the voltage across the electrolytic capacitor 201 decreases. As a result, the voltage applied to the primary winding of converter transformer 203 decreases, so that the absolute value of the negative output voltage on the secondary side also decreases.

On the other hand, if the high-voltage output voltage HV becomes smaller in the direction of 0 V (the absolute value becomes smaller) than the value determined by the value of the reference voltage Vc, the OP-AMP 214 operates in the direction of turning on the transistor 204. To do
The voltage across the electrolytic capacitor 201 increases, and the output voltage on the secondary side of the converter transformer 203 increases in absolute value.

With the above control, the capacitor 20
9 is controlled to a constant voltage (for example, -800 V).

As can be seen from the above equation (1), the smaller the variation of the parameters other than the output voltage HV, the better the control accuracy of the output voltage HV.

Reference numerals 220a to 220d denote the respective developing units 14a to 14d.
The developing bias control circuit outputs individually controlled high voltage HV1 to HV4 to the 14d high voltage contacts 221a to 221d. Reference numeral 220a denotes a developing bias control circuit for yellow, and developing bias control circuits 220b to 220d for other colors have the same circuit configuration as the developing bias control circuit 220a for yellow. Hereinafter, the developing bias control circuit 220a will be described as a representative.

Each of the developing bias control circuits 220a to 220
“d” is connected in parallel to the lines 215 and 216 at both ends of the secondary winding of the converter transformer 203.

In the developing bias control circuit 220a,
Lines 215 and 216 are capacitors C225 and C22
6, C229, and a rectifier circuit composed of diodes 227 and 228. The resistor 224 is for quickly discharging the electric charge charged in the capacitor 229 when the output is turned off.

This rectifier circuit is a circuit that outputs a negative high voltage like the voltage doubler rectifier circuit. However, unlike the above voltage doubler rectifier circuit, a circuit including a high voltage transistor 235 and the like is included between the capacitor 224 and the ground. This circuit relates to a voltage generated at both ends of the capacitor 229 by the rectifier circuit (about -800 V in this case because the voltage is determined by the reference voltage Vc).
By changing the collector-emitter voltage Vce of No. 5, the output voltage of the high-voltage contact 221a as viewed from the ground is made variable. That is, -500 to the high voltage contact 221a.
When it is desired to output V, the voltage Vce between the collector and the emitter of the high-voltage transistor 235 is set to +300 V, whereby the high-voltage contact 221 viewed from the ground is set.
The potential of a is -500 V (= -800 V + 300 V).

As described above, the developing bias control circuit 220
The maximum output (in absolute value) of the high-voltage transistor 235
Of the developing bias control circuit 220a is about −800 V when the high voltage transistor 235 is on (Vce = 0 V) and the minimum output is 0 V when the high voltage transistor 235 is off.
It can be varied between 800V.

Next, the base input signal of the high voltage transistor 235 will be described.

A voltage detection resistor 230 (tolerance ± 1%) is connected to a voltage output line to the contact 221a. The + input terminal of the operational amplifier OP-AMP 234 has a high voltage contact 22
1a and a reference power supply voltage Vb are connected to a resistor 230,
The voltages divided at 231 and 232 are input. S51a
Is a reference voltage signal sent from the image forming control unit, and is a DC voltage corresponding to the high voltage.

The resistance values of the resistors 230, 231 and 232 are R230, R231 and R232, the potential of the high voltage contact 221a as viewed from the ground is HV, and the reference voltage signal S5
Assuming that the voltage value indicated by 1a is S51a, OP-AMP2
In the operation state of 34, the following equation (2) is established.

S51a = (HV / R231 / R232 + Vb / R230 / R232) / (R230 / R231 + R231 / R232 + R230 / R232) (2) In the OP-AMP 234, the positive input terminal voltage is connected to the negative input terminal. The base of the transistor 235 is controlled so as to be equal to the voltage S51a of the high voltage contact 221a.
Appears in

Other developing bias control circuits 220b to 220b
0d operates similarly.

Incidentally, whether or not the output voltage variable method using the high voltage transistor is employed in the developing bias control circuit is substantially determined by how much the output voltage of the developing bias control circuit is required. That is, a high voltage (here, -800V) is applied to the high voltage transistor 235.
Is applied, the high-voltage transistor 235 needs to have a collector-emitter voltage Vce of at least 1000 V or more. Development bias control circuit 22
As the maximum output voltage (absolute value) of 0a is larger, a transistor with a higher breakdown voltage is required, and the cost of the high-voltage transistor 235 increases. In a developing bias control circuit adopting a variable output voltage method using a high voltage transistor, the maximum output voltage (absolute value) is about 1000 V
Since the limit is about 2000 V, the output voltage variable method using a high-voltage transistor is about -500 V (10
This method is suitable for a developing bias control circuit for outputting a voltage of not more than 00V.

[0043]

However, in the above-mentioned conventional developing bias circuit, the converter transformer 2
Each pattern corresponding to the lines 215 and 216 from the secondary winding No. 03 is routed on the printed wiring board. Since a high voltage current flows through these patterns, the distance between the patterns and the peripheral It is necessary to secure a sufficient distance from the circuit. As a result, the area occupied by these patterns on the printed wiring board becomes large, and the mounting efficiency of components becomes poor, and the size of the printed wiring board becomes large.

In addition, since the AC high voltage line before being rectified to the DC voltage is routed, that is, since there are many current loops composed of the secondary coil of the converter transformer 203 and the diodes and capacitors of each rectifier circuit. In addition, noise due to charging current to the capacitor, discharging current from the capacitor, and the like is likely to occur.

When the current in the discharge direction is drawn from the developing bias control circuit 220a due to the influence of another bias such as a charging bias or a load change of the developing device 14a, the current is supplied via the voltage detecting resistor 230. Flows out to the high voltage contact 221a. This current flows through the voltage detection resistor 230, and the potential difference generated causes the developing bias control circuit 2
The output voltage of 20a fluctuates.

Furthermore, with the recent reduction in the price of color laser printers, there is a demand for further reduction in the cost of high voltage circuits.

The present invention has been made in view of the above problems, and has a high efficiency in mounting components on a printed wiring board, reducing noise, reducing output voltage fluctuation, and being inexpensive. It is an object to provide a power supply device for providing a voltage and an image forming apparatus using such a power supply device.

[0048]

According to the first aspect of the present invention, there is provided an image forming apparatus including an image forming unit for forming a toner image by using an electrostatic recording method. A DC power supply circuit that includes a converter transformer and outputs high-voltage DC; and at least one of the DC power supply circuits. The DC output voltage value from the DC power supply circuit is converted by using a semiconductor element. And voltage conversion means for supplying a voltage to a corresponding load.

According to the thirteenth aspect of the present invention, there is provided an image forming apparatus having an image forming means for forming a toner image by using an electrostatic recording method, comprising a converter transformer and outputting a high-voltage DC. And a voltage value of a DC output from the DC power supply circuit,
Voltage converting means for converting the voltage using a constant voltage element and supplying the converted voltage to a corresponding load in the image forming means.

According to the twenty-first aspect of the present invention, there is provided a DC power supply circuit including a converter transformer and outputting a high-voltage DC, and a voltage value of a DC output from the DC power supply circuit provided corresponding to the load. And at least one voltage converting means for converting the voltage using a semiconductor element and supplying the voltage to a corresponding load.

According to the thirty-first aspect of the present invention, there is provided a DC power supply circuit having a converter transformer and outputting a high-voltage DC, and a voltage value of a DC output from the DC power supply circuit provided for a load. There is provided a power supply device having at least one voltage conversion means for converting the voltage using a constant voltage element and supplying the voltage to a corresponding load.

[0052]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 is a circuit diagram showing a configuration of a first embodiment of a developing bias circuit according to the present invention.

Since the configuration of the image forming apparatus to which the developing bias circuit according to the present invention is applied is the same as the configuration described above with reference to FIGS. 9 to 11, in the following description, FIGS. The configuration shown in FIG. 11 is diverted, and description thereof is omitted.

The developing bias circuit according to the present invention applies a high voltage to visualize the latent images formed on the photosensitive drums 18a to 18d to the developing rollers 18a to 18d in the developing units 14a to 14d.

In a tandem type laser printer (image forming apparatus), since four developing units 14a to 14d are provided, it is necessary to apply a high voltage to each of the developing rollers 18a to 18d.

In an image forming apparatus using a negatively charged toner, a negative high voltage is generally used as a high voltage for visualizing a latent image, and the voltage value is generally about -500V.

In the developing bias circuit according to the first embodiment shown in FIG. 1, an output voltage from a reference power supply circuit including a converter transformer 303, a diode 308, a capacitor 309 and the like is converted into four step-down power supply circuits 320a to 320d.
Respectively, and the four developing roller contacts 3
It is supplied to 21a-321d as a developing bias.

That is, S21 is the converter transformer 3
03 is a pulse wave for switching driving, for example, a rectangular wave fixed to 50 kHz, 25% on duty, and 5 V amplitude. When the rectangular wave S21 is input to the base of the transistor 302, the transistor 30
2 repeats on / off according to the rectangular wave S21. By turning on / off the transistor 302, a DC voltage across the electrolytic capacitor 301 is applied to the primary winding of the converter transformer 303 as a pulse-like waveform.
Thereby, from the secondary side of the converter transformer 303,
A boosted pulse-like voltage having the same cycle is output.

The pulse voltage output from the secondary side of the converter transformer 303 is rectified and smoothed by a rectifier circuit including a capacitor C309 and a diode 308, and a high-voltage DC voltage appears at both ends of the capacitor C309.

Next, a circuit portion for controlling the voltage between both ends of the capacitor 309 to a constant value will be described.

Reference numeral 310 denotes a voltage detection resistor for detecting a voltage appearing at both ends of the capacitor 309. A resistor having a high withstand voltage and a high resistance value (for example, a tolerance of the resistance value ± 1%) is used. A voltage obtained by dividing the difference between the voltage between both ends of the capacitor 309 and the reference power supply voltage Vb by the resistors 310, 311 and 312 is input to the + input terminal of the operational amplifier OP-AMP 314. The reference voltage Vc is input to the-input terminal of the OP-AMP 314.

Here, assuming that the resistors 310, 311 and 312 are R310, R311 and R312, respectively, and the voltage across the capacitor 309 is HV, the OP-AMP 314
In the operation state described above, the relationship expressed by the following equation (3) holds between the reference voltage Vc, the voltage HV across the capacitor, and the reference power supply voltage Vb.

Vc = (HV / R311 / R312 + Vb / R310 / R312) / (R310 / R311 + R311 / R312 + R310 / R312) (3) The voltage input to the + input terminal of the OP-AMP 314 is the negative input. The base voltage of the transistor 304 is controlled so as to be equal to the reference voltage Vc connected to the terminal. That is, when the high-voltage output voltage HV (the voltage across the capacitor 309) becomes larger in the negative direction than the value determined by the value of the reference voltage Vc (the absolute value becomes larger), O
The positive input terminal voltage of the P-AMP 314 becomes smaller than the negative input terminal voltage. Therefore, the output of the OP-AMP 314 becomes smaller and operates in a direction to turn off the transistor 304, so that the voltage between both ends of the electrolytic capacitor 301 decreases. As a result, the voltage applied to the primary winding of converter transformer 303 decreases, so that the absolute value of the negative output voltage on the secondary side also decreases.

On the other hand, when the high-voltage output voltage HV becomes smaller in the direction of 0 V (the absolute value becomes smaller) than the value determined by the value of the reference voltage Vc, the OP-AMP 314 operates in the direction of turning on the transistor 304. To do
The voltage across the electrolytic capacitor 301 increases, and the output voltage on the secondary side of the converter transformer 303 increases in absolute value.

With the above control, the capacitor 30
9 is controlled to a constant voltage (for example, -800 V).

As can be seen from the above equation (3), the smaller the variation of the parameters other than the output voltage HV, the better the control accuracy of the output voltage HV.

Reference numeral 320a denotes a step-down power supply circuit for one image forming section (yellow in the example in the figure). Since the configurations of the four step-down power supply circuits 320a to 320d are the same, the step-down power supply circuit 320a will be described as a representative.

In the step-down power supply circuit 320a to which a DC voltage rectified to a constant voltage (for example, -800 V) is input, a high-voltage transistor 325 is provided in series between the input terminal and the developing roller contact 321a, and its collector / emitter is provided. The voltage Vce is variably controlled. As a result, the input voltage
800V (absolute value), and the developing roller contact 321
Any voltage between the input voltage (absolute value) and 0 V can be applied to a. That is, when it is desired to output −500 V to the developing roller contact 321 a, the collector-emitter voltage Vce of the high-voltage transistor 325 is set to +
The potential of the developing roller contact 321a as viewed from the ground is -500V.
(= −800 V + 300 V). The maximum output (in absolute value) of the step-down power supply circuit 320a is about -800 V when the high voltage transistor 325 is on (Vce = 0 V), and the minimum output is 0 when the high voltage transistor 325 is off.
V, and the (absolute value) output of the step-down power supply circuit 320a can be varied between 0V and about -800V.

To detect the output voltage to the developing roller contact 321a, a voltage detecting resistor 330 (tolerance ± 1%) is connected to the output line to the developing roller contact 321a.
A voltage obtained by dividing the output voltage to the developing roller contact 321a and the reference power supply voltage Vb by the resistors 330, 331, and 332 is input to the + input terminal of the operational amplifier OP-AMP 334.

S31a is a reference voltage signal sent from the image forming control unit, and is a DC voltage corresponding to the high voltage. If the voltage value indicated by the reference voltage signal S31a is S31a, the resistance values of the resistors 330, 331, and 332 are R330, R331, and R332, respectively, and the potential of the developing roller contact 321a as viewed from the ground is HV, OP-
In the operating state of the AMP 334, the following equation (4) is established.

S31a = (HV / R331 / R332 + Vb / R330 / R332) / (R330 / R331 + R331 / R332 + R330 / R332) (4) In the OP-AMP 334, the positive input terminal voltage is connected to the negative input terminal. A voltage that is equal to the reference voltage signal voltage value S31a is output.

Reference numeral 338 denotes a high withstand voltage capacitor, which includes a high voltage portion including a high voltage transistor 325 and the like and an OP-AMP.
334 and the like.

Reference numeral 337 denotes a transistor, which is turned on and off when a rectangular wave S21 for driving the converter transformer 303 is input to the base. When the transistor 337 is turned on and off, the OP-AMP
The output voltage from 334 becomes a pulse voltage,
5, 336 and applied to one end of the capacitor 338.

At the other end of the capacitor 338, a pulse voltage corresponding to the pulse voltage applied to the one end appears, and the pulse voltage is generated by a rectifier circuit including diodes 339 and 340, a capacitor 342, and a discharge resistor 341. It is smoothed and applied between the base and the emitter of the high voltage transistor 325.

That is, in the step-down power supply circuit 320a, a base current corresponding to the output voltage of the OP-AMP 334 flows through the high-voltage transistor 325. Therefore, the collector-emitter voltage Vce of the high-voltage transistor 325 changes to the output voltage of the OP-AMP 334. It will be a value according to. That is, the output voltage of the step-down power supply circuit 320a is controlled to a voltage corresponding to the reference voltage signal S31a.

The other step-down power supply circuits 320b to 320d perform the same operation.

Whether or not the variable output voltage system using the high voltage transistor 325 is adopted for the step-down power supply circuit 320a is substantially determined by how much output voltage of the step-down power supply circuit 320a is required. That is,
A high voltage (here, -80) is applied to the high voltage transistor 325.
0V) is applied, the high-voltage transistor 325 has a collector-emitter voltage Vce of at least 10
It is necessary to be 00V or more. Step-down power supply circuit 32
As the maximum output voltage (absolute value) of 0a is larger, a transistor with a higher breakdown voltage is required, and the cost of the high-voltage transistor 325 increases. In a step-down power supply circuit employing a variable output voltage method using a high-voltage transistor, the maximum output voltage (absolute value) is about 1000 V to 200 V.
Since the limit is about 0 V, the output voltage variable method using a high-voltage transistor is suitable for a step-down power supply circuit for outputting a voltage of about -500 V (1000 V or less).

Next, the operation of the developing bias circuit will be described with reference to FIGS.

FIG. 2 is a flowchart showing the operation of the developing bias circuit, and FIG. 3 is a flowchart showing the rectangular wave S21 (A), the reference voltage signal S31a (B), the high voltage output voltage (C) from the step-down power supply circuit 320a, and It is a timing chart of time t (D).

First, the rectangular wave S21 for driving the converter transformer 303 is not supplied to the developing bias circuit (OF
F), the reference voltage signal S31a is set to the value of the reference power supply voltage Vb (ST601). Since there is no input of the rectangular wave S21, there is no output voltage on the secondary side of the converter transformer 303, so that the output voltage of the step-down power supply circuit 320a is 0V. Here, since the resistance value of the voltage detection resistor 330 is sufficiently larger than the resistances 331 and 332, OP-A
The potential on the + input terminal side of MP334 is the reference power supply voltage Vb
Is divided by the resistor 331 and the resistor 332, which is lower than the voltage (= Vb) on the-input terminal side. Therefore, the output of the OP-AMP 334 becomes almost 0 V, and the high voltage transistor 325 It is turned off (electrically open).

When the line 315 is at 0 V, the resistors 310, 311 and 312 are connected so that the + input terminal voltage of the OP-AMP 314 becomes higher than the-input terminal voltage.
Each resistance value is set in advance. Therefore, the square wave S21
Is not input, the transistor 304 is on.

Next, when the rectangular wave S21 for driving the converter transformer 303 is supplied to the developing bias circuit, the time t
Is set to 0 (ST602, FIGS. 3A and 3D). Since the transistor 304 is on, the electrolytic capacitor 301
Is charged, and a pulse voltage is generated on the secondary side of the converter transformer 303 by the input of the square wave S21,
On line 315, a DC voltage controlled to a constant voltage of about -800V appears. However, at this time, since the high-voltage transistor 325 is off, no high-voltage output voltage appears at the developing roller contact 321a (FIG. 3C).

Since the rectangular wave S21 is also applied to the base of the transistor 337, when the output voltage of the OP-AMP 334 rises from 0V, the capacitor 338 can be charged and discharged.

It is determined whether or not the time t has reached the predetermined time Ta (ST603, FIG. 3D). If not, the time t is incremented (ST604). If it has reached, the reference voltage signal S31a is set to the value Vd (Vd <Vb) (ST605, FIG. 3B). Thereby, OP-A
Since the-input terminal voltage of MP334 is lower than the + input terminal voltage, a voltage appears at the output terminal of OP-AMP 334 so as to satisfy the following expression (5), and the high-voltage transistor 3
25 conducts. Thereby, the developing roller contact 321a
A voltage −V22 appears (ST606, FIG. 3C).

Vd = (− V22 · R331 · R332 + Vb · R330 · R332) / (R330 · R331 + R331 · R332 + R330 · R332) (5) Next, whether or not the time t has reached the predetermined time Tb (ST607, FIG. 3D), and if not reached, the time t is incremented (ST608). If it has reached, that is, the rectangular wave S2 for driving the converter transformer 303
When a predetermined time Tb has elapsed after the supply of the reference signal 1, the reference voltage signal S31a is returned to the value Vb, and the supply of the rectangular wave S21 is stopped (ST609, FIG. 3A,
B). As a result, the transistor 325 is turned off, the output from the secondary side of the converter transformer 303 disappears, and the output voltage to the developing roller contact 321a becomes 0 V (ST610, FIG. 3C).

One of the differences between the conventional developing bias circuit shown in FIG. 12 and the developing bias circuit in the first embodiment shown in FIG. 1 lies in the wiring of the high-voltage transistor. In the conventional developing bias circuit shown in FIG.
03, between the output voltage line 215 from the secondary side and the ground, the base terminal of the high-voltage transistor 235 is located on the low-voltage side, and the low-voltage side OP-AMP
234 can be controlled directly.

On the other hand, in the first embodiment shown in FIG.
Since the high-voltage transistor 325 is arranged in the middle of the high-voltage output line, the base terminal of the high-voltage transistor 325 is also located on the high-voltage side, and cannot be directly controlled from the low-voltage side OP-AMP 334. It is necessary to control the high voltage transistor 325 after the voltage section and the high voltage section are DC-insulated. Therefore, in the first embodiment, the high-voltage capacitor 338 is used to insulate the low-voltage section and the high-voltage section in a DC manner, and the converter transformer 30
The DC control output of the OP-AMP 334 is switched by a transistor using the rectangular wave S21 for driving the AC control output 3 and the AC control output thus obtained is
It is sent to the high voltage section via the high voltage capacitor 338. The high-voltage section rectifies and smoothes the transmitted AC control output and applies the rectified and smoothed control output to the base terminal of the high-voltage transistor 325.

In the first embodiment, the signal input to the base of the transistor 337 is not limited to the rectangular wave S21 for driving the converter transformer 303, and another rectangular wave may be used.

Further, in the conventional developing bias circuit shown in FIG. 12, the AC high voltage lines 215 and 216 are routed. However, in the first embodiment, the rectified DC voltage (−800 V) line 315 is connected. In this case, noise is unlikely to be generated from the line 315. Furthermore, since there is only one set of printed wiring board patterns corresponding to the lines 315, the area occupied on the printed wiring board is reduced by half.

In the first embodiment, there are four developing roller contacts 321a to 321d, and the step-down power supply circuit is
However, instead of this, the color (yellow,
In the case of an image forming apparatus provided with two developing roller contacts for magenta and cyan) and for black, it is only necessary to provide two step-down power supply circuits. Needless to say, it should be increased. In addition, it goes without saying that the present invention can be applied not only to the developing bias circuit but also to a combination with another bias circuit such as a charging bias circuit or another bias.

(Second Embodiment) Next, a second embodiment will be described.

FIG. 4 is a circuit diagram showing a configuration of a developing bias circuit according to the second embodiment.

The configuration of the image forming apparatus to which the developing bias circuit according to the second embodiment is applied is the same as the configuration described above with reference to FIGS. 9 to 11, and will be described below. The configuration shown in FIGS. 9 to 11 is diverted, and description thereof is omitted.

The configuration and operation of the portion of the developing bias circuit shown in FIG. 4 except for the step-down power supply circuits 420a to 420d are the same as those of the first embodiment,
The description is omitted. Step-down power supply circuits 420a to 420d
Have the same configuration, the step-down power supply circuit 420a will be described as a representative.

In the second embodiment, an optical semiconductor element 425 is used instead of the high voltage transistor 325 in the first embodiment shown in FIG.

The optical semiconductor element 425 is an element called a photo MOS relay, and includes a photodiode, a solar cell, and a MOS-FET in one package.
The photodiode and the MOS-FET have an insulating structure, and there is a MOS-FET having a withstand voltage between the drain and the source of about several hundred volts to about 2,000 volts.

The base current of the transistor 437 changes according to the output of the OP-AMP 434 on the low voltage side, and the resulting collector current of the transistor 437 flows to the photodiode of the optical semiconductor element 425. When the current flowing through the photodiode increases, the electromotive force in the solar cell increases, and the MOS-FET is controlled to turn on.

Step-down power supply circuit 4 according to second embodiment
In 20a, the low voltage portion and the high voltage portion can be separated by the optical semiconductor element 425. Therefore, the high voltage capacitor 338 used in the first embodiment, the rectangular wave S21 for charging and discharging the capacitor 338, the transistor 337, the diodes 339 and 340, the capacitor 3
The rectifying / smoothing circuit composed of 42 and the like becomes unnecessary, and the step-down power supply circuit 420a is simplified.

(Third Embodiment) Next, a third embodiment will be described.

FIG. 5 is a circuit diagram showing a configuration of a developing bias circuit according to the third embodiment.

The configuration of the image forming apparatus to which the developing bias circuit according to the third embodiment is applied is the same as the configuration described above with reference to FIGS. 9 to 11, and will not be described below. The configuration shown in FIGS. 9 to 11 is diverted, and description thereof is omitted.

The configuration of the developing bias circuit according to the third embodiment is basically the same as the configuration of the developing bias circuit according to the first embodiment shown in FIG.
The same components are denoted by the same reference numerals and description thereof will be omitted.

In the third embodiment, only a portion corresponding to the yellow step-down power supply circuit 320a in the first embodiment is simplified. Other three step-down power supply circuits 320
b to 320d have the same configuration as in the first embodiment.

The developing bias circuit generally has a voltage of about -500V.
It is often required to output the voltage before and after.
The maximum voltage difference between the voltages applied to the three developing roller contacts 321a to 321d is about 150V. Focusing on this point, the step-down power supply circuit for yellow can be simplified as follows.

S21 is a pulse wave for switching driving of the converter transformer 303, for example, 50 k
A rectangular wave having a fixed frequency of 25 Hz, an on-duty of 25%, and an amplitude of 5 V is used. The square wave S21 is the transistor 302
, The transistor 302 repeats on / off in accordance with the rectangular wave S21. When the transistor 302 is turned on / off, the electrolytic capacitor 3
01 is switched and applied to the primary winding of the converter transformer 303 as a pulsed voltage. As a result, a boosted pulse-like voltage having the same period is output from the secondary side of the converter transformer 303.

The pulse voltage output from the secondary side of the converter transformer 303 is rectified and smoothed by a rectifier circuit including a capacitor C309 and a diode 308, and a high-voltage DC voltage appears at both ends of the capacitor C309. The line 315 is connected to the capacitor C309.

Reference numeral 319 denotes a high-voltage Zener diode arranged in series between the line 315 and the developing roller contact 321a for the first color (for yellow), and its Zener voltage is, for example, 200V. Therefore, when, for example, −700 V is output to both ends (line 315) of the capacitor C 309, the developing roller contact 321 a is −500 V (= −700 V) obtained by subtracting 200 V (absolute value) of the voltage drop due to the Zener diode. − (− 200 V)) appears.

Reference numeral 310 denotes a voltage detection resistor for detecting a voltage appearing at the developing roller contact point 321a, and a high withstand voltage and high precision (for example, a tolerance of resistance value ± 1%) is used. A voltage obtained by dividing the output voltage appearing at the developing roller contact 321a and the reference power supply voltage Vb by the resistors 310, 311 and 312 is input to the + input terminal of the operational amplifier OP-AMP 314. Operational Amplifier OP-A
A reference voltage Vc is applied to a negative input terminal of MP314.

Here, the resistance values of the resistors 310, 311 and 312 are R310, R311 and R312, respectively.
Assuming that the output voltage appearing at the developing roller contact 321a is HV, the following equation (6) holds in the operating state of the OP-AMP 314.

Vc = (HV / R311 / R312 + Vb / R310 / R312) / (R310 / R311 + R311 / R312 + R310 / R312) (6) The OP-AMP 314 has a positive input terminal voltage connected to the negative input terminal. A voltage equal to the reference voltage Vc is output to the base of the transistor 304. That is, the voltage HV appearing at the developing roller contact 321a is equal to the reference voltage V
When the value becomes larger in the negative direction than the value determined by the value of c (the absolute value becomes larger), the + input terminal voltage of the OP-AMP 314 becomes smaller than the-input terminal voltage. Therefore, the output of the OP-AMP 314 becomes small, and the transistor 304 is turned off, so that the voltage across the electrolytic capacitor 301 decreases. As a result, the voltage applied to the primary winding of converter transformer 303 decreases, so that the absolute value of the negative output voltage obtained by rectification and smoothing on the secondary side of converter transformer 303 also decreases.

On the other hand, the voltage HV appearing at the developing roller contact point 321a is smaller than the value determined by the value of the reference voltage Vc by 0.
When it becomes smaller in the direction of V (the absolute value becomes smaller), OP
Since −AMP 314 operates in a direction to turn on the transistor 304, the voltage across the electrolytic capacitor 301 increases, and the absolute value of the negative output voltage obtained by rectifying and smoothing on the secondary side of the converter transformer 303 increases.

By the operation control as described above, the voltage HV appearing at the developing roller contact 321a becomes a constant voltage (-500
V), and a voltage of about −700 V is output to the high voltage line 315 by the zener voltage 200 V of the zener diode 319.

As described above, the output voltage of -500 V is applied to the developing roller contact 321a of the first color, and 0 V is applied to the other developing roller contacts 321b to 321d of the second and subsequent colors.
An arbitrarily varied voltage in the range of -700 V (-650 V in consideration of variation) is applied.

When the current flowing through the Zener diode 319 is small and the Zener voltage cannot be obtained normally,
It is preferable to arrange a high withstand voltage resistor (not shown) between the developing roller contact 321a and the ground so that a dummy current flows.

In the third embodiment, the zener diode 319 is used to simplify the step-down power supply circuit for the first color (for yellow). In this developing bias circuit, as long as the step-down power supply circuit of the first color operates to supply no voltage to the developing roller contact 321a, the other developing roller contacts 321b
To 321d.

Therefore, in an image forming apparatus provided with a black-and-white print mode mode in which only the developing bias for black (the fourth color) is turned on, the step-down power supply circuit for the first color (for yellow) is not simplified. In the fourth-color (black) step-down power supply circuit, it is desirable to use a Zener diode for simplification.

In the third embodiment, the circuit configuration of the first-color step-down power supply circuit can be greatly simplified as compared with the first embodiment, and therefore the cost can be reduced.

(Fourth Embodiment) Next, a fourth embodiment will be described.

FIG. 6 is a circuit diagram showing a configuration of a developing bias circuit according to the fourth embodiment.

The configuration of the image forming apparatus to which the developing bias circuit according to the fourth embodiment is applied is the same as the configuration described above with reference to FIGS. 9 to 11, and will not be described below. The configuration shown in FIGS. 9 to 11 is diverted, and description thereof is omitted.

Since the configuration of the developing bias circuit according to the fourth embodiment is basically the same as the configuration of the developing bias circuit shown in FIG. 12, the same components are denoted by the same reference numerals. The description is omitted.

In the fourth embodiment, only the portion corresponding to the developing bias control circuit 220a for yellow in the developing bias circuit shown in FIG. 12 is simplified. The other three developing bias control circuits 220b to 220d
Has the same configuration as the developing bias circuit shown in FIG.

In the fourth embodiment, the diode 207,
Similarly to the third embodiment, a zener diode 219 is provided between the output side of the rectifier circuit including the capacitor 208 and the capacitor 209 and the first color at the connection point between the zener diode 219 and the resistor 210. (For yellow)
Of the developing roller contact 221a.

In the same manner as in the third embodiment, in the developing bias control circuit for the first color, a DC voltage of -700 V is output to a connection point between the output side of the rectifying circuit and the Zener diode 219, and the developing roller A DC voltage of -500 V is output to the contact 221a. Developing roller contact 2 for the second and subsequent colors
Arbitrarily varied voltages in the range of 0 V to -700 V (-650 V in consideration of variations) are applied to 21b to 221d.

In an image forming apparatus provided with a black-and-white printing mode mode in which only the developing bias for black (the fourth color) is turned on, the developing bias control circuit for the first color (for yellow) is not simplified. In the developing bias control circuit for the fourth color (black), it is desirable to use a Zener diode for simplification.

In the fourth embodiment, the configuration of the developing bias control circuit for the first color can be greatly simplified as compared with the conventional developing bias circuit shown in FIG. 12, and therefore the cost can be reduced.

(Fifth Embodiment) Next, a fifth embodiment will be described.

FIG. 7 is a circuit diagram showing a configuration of a developing bias circuit according to the fifth embodiment.

The configuration of the image forming apparatus to which the developing bias circuit according to the fifth embodiment is applied is the same as the configuration described above with reference to FIGS. 9 to 11, and will be described below. The configuration shown in FIGS. 9 to 11 is diverted, and description thereof is omitted.

The configuration of the developing bias circuit according to the fifth embodiment is basically the same as the configuration of the developing bias circuit according to the third embodiment shown in FIG.
The same components are denoted by the same reference numerals and description thereof will be omitted.

In the fifth embodiment, a varistor 31 is used instead of the Zener diode 319 in the third embodiment.
8 is used.

That is, if the varistor 318 having a varistor voltage of 200 V is used, as in the third embodiment, in the step-down power supply circuit of the first color, the output side of the rectifier circuit including the diode 308 and the capacitor 309 is connected to the varistor 318. A DC voltage of -700 V is output to the connection point, and a DC voltage of -500 V is output to the developing roller contact 321a. 0V is applied to the developing roller contacts 321b to 321d for the second and subsequent colors.
An arbitrarily varied voltage in the range of -700 V (-650 V in consideration of variation) is applied.

In an image forming apparatus provided with a black-and-white print mode mode in which only the developing bias for black (the fourth color) is turned on, the step-down power supply circuit for the first color (for yellow) is not simplified. In the step-down power supply circuit of the fourth color (black), it is desirable to use a varistor for simplification.

In the fourth embodiment, the circuit configuration of the first-color step-down power supply circuit can be greatly simplified as compared with the first embodiment, and therefore the cost can be reduced.

(Sixth Embodiment) Next, a sixth embodiment will be described.

FIG. 8 is a circuit diagram showing a configuration of a developing bias circuit according to the sixth embodiment.

The configuration of the image forming apparatus to which the developing bias circuit according to the sixth embodiment is applied is the same as the configuration described above with reference to FIGS. 9 to 11, and will be described below. The configuration shown in FIGS. 9 to 11 is diverted, and description thereof is omitted.

The configuration of the developing bias circuit according to the sixth embodiment is basically the same as the configuration of the developing bias circuit according to the first embodiment shown in FIG.
The same components are denoted by the same reference numerals and description thereof will be omitted.

In the sixth embodiment, the resistors 322a to 322
2d are provided between the developing roller contacts 321a to 321d and the ground, respectively. In the following, the operation of the resistor 322a will be described for the step-down power supply circuit 320a for yellow, but the same applies to the resistors 322b to 322d.

Since the developing bias circuit generates a negative high voltage, the direction of the current flowing to the load (developing device 14a) connected to the developing roller contact 321a is usually
This is the direction in which the current flows from the load side toward the step-down power supply circuit 320a (I21). However, due to the influence of the charging bias (for example, -1000 V) applied to the charger 16a and other biases, the voltage of the developing device 14a side may be rarely lower than the output voltage of the step-down power supply circuit 320a. At this time, a current (I24) in the discharge direction flows from the step-down power supply circuit 320a toward the developing roller contact 321a.

Since the transistor 325 is mounted in a direction in which the current I24 does not flow, if the resistor 322a is not provided, the current I24 in the discharge direction is not used.
Is connected to a reference power supply V via resistors 331, 332, and 330.
b or ground toward the developing roller contact 321a. Therefore, the current I in the discharge direction
The current I22 flowing through the resistor 330 with the occurrence of the current 24 becomes substantially the same as the current I24. Since the current I22 flows through the voltage detection resistor 330, the current I22
Causes a detection error in the voltage detection resistor 330, and the developing bias voltage appearing at the developing roller contact point 321a fluctuates due to the generation of the current I24 in the discharge direction.

The resistor 322a is provided to solve this problem, and causes the current I23 to flow through the resistor 322a when the current I24 in the discharge direction is generated. That is, the discharge current I24 is changed to the current I22.
And the current I23.

By providing this resistor 322a, the current I22 flowing through the voltage detection resistor 330 is reduced, and the current I2
2, the fluctuation in voltage appearing in the developing bias output voltage can be suppressed to a level that does not cause a problem in the printing quality of the image forming apparatus.

[0145]

As described in detail above, claims 1 and 1
According to the invention of claim 21 or claim 31, a DC power supply circuit including a converter transformer and outputting a high-voltage DC, and a voltage of a DC output from the DC power supply circuit provided corresponding to the load. At least one voltage converting means for converting a value using a semiconductor element or a constant voltage element and supplying the converted value to a corresponding load.

Since the DC output from the DC power supply circuit is input to the voltage conversion means, unlike the conventional case, the high voltage AC line is not routed, thereby reducing the generation of noise. Since only a pattern corresponding to one set of high-voltage lines needs to be provided on the printed wiring board, the area occupied by the input line pattern of the voltage conversion means on the printed wiring board is reduced by half, and the efficiency of mounting components on the printed wiring board Will be better.

According to the invention of claim 5, claim 16, claim 17, claim 23, claim 32, or claim 33, the semiconductor element is an optical semiconductor element, and the constant voltage element is a zener diode or It is a varistor.

As a result, the circuit configuration can be greatly simplified, and the cost can be reduced.

According to the twelfth aspect of the present invention, each of the voltage converting means includes a resistor inserted between the output terminal and the ground.

As a result, the output voltage fluctuation is reduced,
In an image forming apparatus using such a power supply device, image quality is stabilized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a first embodiment of a developing bias circuit according to the present invention.

FIG. 2 is a flowchart illustrating an operation of a developing bias circuit.

FIG. 3 shows a rectangular wave S21 (A) and a reference voltage signal S31a.
4B is a timing chart of the high-voltage output voltage (C) from the step-down power supply circuit and the time t (D).

FIG. 4 is a circuit diagram showing a configuration of a developing bias circuit according to a second embodiment.

FIG. 5 is a circuit diagram showing a configuration of a developing bias circuit according to a third embodiment.

FIG. 6 is a circuit diagram showing a configuration of a developing bias circuit according to a fourth embodiment.

FIG. 7 is a circuit diagram showing a configuration of a developing bias circuit according to a fifth embodiment.

FIG. 8 is a circuit diagram showing a configuration of a developing bias circuit according to a sixth embodiment.

FIG. 9 is a diagram illustrating a configuration of a tandem type color image forming apparatus.

FIG. 10 is a diagram showing a structure of a scanner unit.

FIG. 11 is a diagram showing an arrangement of each high-voltage bias circuit used in each image forming unit.

FIG. 12 is a circuit diagram showing a configuration of a conventional developing bias circuit including one converter transformer.

[Explanation of symbols]

16a to 16d Charger 18a to 18d Photoconductor drum 14a to 14d Developing device 17a to 17d Developing roller 19a to 19d Transfer device 23 Fixing device 30a to 30d High-voltage bias circuit (charging bias) 31a to 31d High-voltage bias circuit (transfer bias) 32a To 32d high-voltage bias circuit (developing bias) 302 transformer driving transistor 303 converter transformer 320a to 320d step-down power supply circuit (voltage conversion means) 321a to 320d developing roller contact 325 high-voltage transistor (semiconductor element, high voltage transistor) 338 high-voltage capacitor (high Withstand voltage capacitor) 330 Voltage detection resistor 314, 334 Operational amplifier OP-AMP 318 Varistor (constant voltage element) 319 Zener diode (constant voltage element) 425 Optical semiconductor element (semiconductor element) S 21 Square wave (pulse signal) S31a Reference voltage signal (control signal) Vb Reference power supply voltage I21 Sink current I24 Discharge current

Continued on front page F-term (reference) 2H027 ED09 JA20 ZA01 2H030 AA05 AB02 AD19 BB34 BB44 5G065 AA00 AA08 DA07 EA01 FA02 GA04 HA01 JA01 LA01 MA10 NA01 NA02 NA04 NA05 NA06 NA07 NA09 5H730 AA01 AA08 AS04 BB41 EE57 EE65 FD01 FG01 XC20

Claims (36)

[Claims] 1. An image forming apparatus having an image forming means for forming a toner image by using an electrostatic recording method, comprising: a DC power supply circuit having a converter transformer and outputting a high-voltage DC; An image forming apparatus comprising: a voltage converting unit that converts a voltage value of a DC output from the DC power supply circuit using a semiconductor element and supplies the converted voltage value to a corresponding load in the image forming unit. 2. An image forming apparatus according to claim 1, wherein said image forming means comprises a plurality of color-specific image forming means for forming toner images of different colors on a plurality of image carriers. . 3. The image according to claim 1, wherein the load comprises a plurality of developing units for developing the latent images formed on the plurality of image carriers into toner images of different colors, respectively. Forming equipment. 4. The image forming apparatus according to claim 1, wherein the semiconductor element is a high breakdown voltage transistor inserted in series between the DC power supply circuit and the corresponding load. 5. The image forming apparatus according to claim 1, wherein the semiconductor element is an optical semiconductor element inserted in series between the DC power supply circuit and the corresponding load. 6. The image forming apparatus according to claim 5, wherein the optical semiconductor element is a photo MOS relay including a photodiode, a solar cell, and a MOS-FET. 7. The image forming apparatus according to claim 1, wherein said DC power supply circuit includes voltage control means for controlling a DC voltage output from said DC power supply circuit to a constant value. 8. The semiconductor device is a high withstand voltage transistor having an emitter connected to the DC power supply circuit side and a collector connected to a corresponding load side, and the voltage conversion means includes a pulse signal corresponding to a control signal. A high-voltage part that rectifies the pulse signal and applies it to the base of the high-voltage transistor, and a high-voltage capacitor that connects the low-voltage part and the high-voltage part. The image forming apparatus according to claim 1, wherein: 9. In the DC power supply circuit, a DC voltage is switched by an input pulse signal and supplied to the primary side of the converter transformer, and the same signal as the pulse signal is supplied to the low voltage portion. The image forming apparatus according to claim 8, wherein: 10. The image forming apparatus according to claim 1, wherein said voltage converting means converts a voltage value of a DC output from said DC power supply circuit so that its absolute value becomes smaller. 11. The image forming apparatus according to claim 1, wherein a DC voltage output from the DC power supply circuit and a DC voltage output from the voltage conversion unit have a negative polarity. 12. The image forming apparatus according to claim 1, wherein each of said voltage converting means includes a resistor inserted between an output terminal and a ground. 13. An image forming apparatus provided with an image forming means for forming a toner image by using an electrostatic recording method, comprising: a DC power supply circuit having a converter transformer and outputting a high-voltage DC; An image forming apparatus comprising: a voltage converting unit that converts a voltage value of a DC output from the DC power supply circuit using a constant voltage element and supplies the converted voltage value to a corresponding load in the image forming unit. 14. The image forming means according to claim 13, wherein said image forming means comprises a plurality of color-specific image forming means for forming toner images of different colors on a plurality of image carriers.
The image forming apparatus as described in the above. 15. The image according to claim 13, wherein said load comprises a plurality of developing means for developing latent images respectively formed on a plurality of image carriers into toner images of different colors. Forming equipment. 16. The image forming apparatus according to claim 13, wherein said constant voltage element is a Zener diode. 17. The image forming apparatus according to claim 13, wherein said constant voltage element is a varistor. 18. The image forming apparatus according to claim 13, wherein said DC power supply circuit includes voltage control means for controlling a DC voltage output from said voltage conversion means to a constant value. 19. The image forming apparatus according to claim 13, wherein said voltage converting means converts a voltage value of a DC output from said DC power supply circuit so that its absolute value becomes smaller. 20. The image forming apparatus according to claim 13, wherein the DC voltage output from the DC power supply circuit and the DC voltage output from the voltage conversion unit have a negative polarity. 21. A DC power supply circuit having a converter transformer and outputting a high-voltage DC, provided corresponding to a load, and converting a DC output voltage value from the DC power supply circuit using a semiconductor element, A power supply device comprising at least one voltage conversion means for supplying a corresponding load. 22. The power supply device according to claim 21, wherein the semiconductor element is a high breakdown voltage transistor inserted in series between the DC power supply circuit and the corresponding load. 23. The power supply device according to claim 21, wherein said semiconductor element is an optical semiconductor element inserted in series between said DC power supply circuit and said corresponding load. 24. A photo MOS device comprising a photodiode, a solar cell, and a MOS-FET.
The power supply device according to claim 23, wherein the power supply device is a relay. 25. The power supply device according to claim 21, wherein said DC power supply circuit includes voltage control means for controlling a DC voltage output from said DC power supply circuit to a constant value. 26. The semiconductor device according to claim 26, wherein the semiconductor element is a high-voltage transistor having an emitter connected to the DC power supply circuit side and a collector connected to a corresponding load side, and wherein the voltage converting means includes a pulse signal corresponding to a control signal. A high-voltage part that rectifies the pulse signal and applies it to the base of the high-voltage transistor, and a high-voltage capacitor that connects the low-voltage part and the high-voltage part. The power supply device according to claim 21, wherein: 27. In the DC power supply circuit, a DC voltage is switched by an input pulse signal and supplied to the primary side of the converter transformer, and the same signal as the pulse signal is supplied to the low voltage portion. The power supply device according to claim 26, wherein: 28. The power supply device according to claim 21, wherein said voltage conversion means converts a voltage value of a DC output from said DC power supply circuit so that its absolute value becomes smaller. 29. The power supply device according to claim 21, wherein the DC voltage output from the DC power supply circuit and the DC voltage output from the voltage converter are negative. 30. The power supply device according to claim 21, wherein each of said voltage conversion means includes a resistor inserted between an output terminal and a ground. 31. A DC power supply circuit having a converter transformer and outputting a high-voltage DC, and is provided corresponding to a load, and converts a DC output voltage value from the DC power supply circuit using a constant voltage element. And at least one voltage converting means for supplying a corresponding load. 32. The power supply device according to claim 31, wherein said constant voltage element is a Zener diode. 33. The power supply device according to claim 31, wherein the constant voltage element is a varistor. 34. The power supply device according to claim 31, wherein said DC power supply circuit includes voltage control means for controlling a DC voltage output from said voltage conversion means to a constant value. 35. The power supply device according to claim 31, wherein said voltage conversion means converts a voltage value of a DC output from said DC power supply circuit so that its absolute value becomes smaller. 36. The power supply device according to claim 31, wherein the DC voltage output from the DC power supply circuit and the DC voltage output from the voltage conversion means are negative.