JPH02226408A - Switching power supply device - Google Patents

Abstract

PURPOSE:To permit a detection signal from an output detection means to stably control a power supply output without being affected by noise by installing a voltage drop means dropping a detection signal immediately before the input terminal of a driving means inputting the detection signal. CONSTITUTION:The voltage drop means 20 dropping the detection signal is installed immediately before the input terminal of the driving means 10 and 11 inputting the detection signal. Consequently, the detection signal which the output detection means 17 and 18 have detected is transmitted to the driving means 10 and 11 at a large signal level, and voltage-dropped by the voltage drop means 20 immediately before the input terminal of the driving means 10 and 11. Thus, the signal can be dropped less than the maximum allowance input voltage of an A/D converter in the driving means 10 and 11. Since the detection signal is fed back at the large level while the input condition of the driving means 10 and 11 is satisfied, noise which has appeared midway on a line is voltage-dropped and is converted into a low level immediately before it is inputted to the driving means 10 and 11. Thus, the power supply output can stably be controlled without being affected by noise.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a switching power supply device, and particularly to a switching power supply device in which an output detection means and a driving means are integrated.

[Conventional technology]

For example, electrophotographic devices that perform electrostatic recording require multiple high-voltage power supplies for the recording process, and in order to record high-quality images, the voltage or current of these high-voltage power supplies must be adjusted with high precision. It is necessary to set a standard value and maintain it stably.

As such a power supply device, for example, Japanese Patent Application Laid-Open No. 60-15
The one described in Publication No. 3518 is known.

This power supply device switches a high-voltage power supply unit and a copying process control unit independently from each other, and converts a detection signal outputted by an output detection means consisting of a variable resistor of the high-voltage power supply unit into an A/D converter provided in the copying process control unit. Feedback control is performed so that the data input to the A/D converter and output from the A/D converter become a target value corresponding to a preset reference value of the high voltage power supply output.

[Problem to be solved by the invention]

However, according to such a conventional power supply device, the detection signal from the output detection means is directly input to the A/D converter provided in the copying process control unit, so the level of the detection signal depends on the level of the A/D converter. Limited to below the maximum allowable input voltage.

For this reason, the detection signal level is small, and while the detection signal is being sent from the high-voltage power supply unit to the copying process control unit, it may be affected by noise, especially noise from other high-voltage discharges, resulting in unstable control or output ripple. The problem was that it was growing.

The present invention has been made in view of the above points, and it is an object of the present invention to stably control the power output in a switching power supply device without the detection signal from the output detection means being affected by noise.

[Means to solve the problem]

In order to achieve the above object, the present invention has a series circuit consisting of the primary winding of a conversion transformer connected to a DC power source and a switching element, and AC power induced in the secondary winding of the conversion transformer. Alternatively, an output circuit that rectifies and smoothes and outputs DC power, an output detection means that detects the voltage or current of AC or DC power outputted by this output circuit and outputs a detection signal, and a detection signal outputted by this output detection means. In a switching power supply device consisting of a drive means that stabilizes AC or DC power by outputting a drive signal that turns on and off a switching element according to a signal, the terminal immediately before the input terminal of the drive means that inputs the detection signal. A step-down means is provided to step down the detection signal.

[For production]

By configuring as described above, the present invention sends the detection signal detected by the output detection means to the drive means at a large signal level, and the detection signal sent by the step-down means immediately before the input terminal of the drive means. By lowering the voltage, the driving means A/
The input voltage can be lower than the maximum allowable input voltage of the D converter.

Therefore, by feeding back the detection signal at a high level while satisfying the input conditions of the driving means, the noise that has entered the line along the way is stepped down and converted to a low level just before inputting to the driving means. It is possible to stably control the power output without being affected by

〔Example〕

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

FIG. 4 is an explanatory diagram of the photosensitive drum and its surroundings of an electrophotographic apparatus using a high-voltage power supply equipped with a switching power supply according to the present invention.

In FIG. 4, a charger 2. Developing device 3. Static elimination lamp 4. A transfer charger 52, a separation charger 6, a cleaning device 7, and a static elimination lamp 8 are provided.

When forming an image using an electrophotographic apparatus configured as described above, first, the photosensitive drum 1, which has been neutralized in advance, is
The surface of the device is charged to a predetermined potential by the charger 2.

Next, through an optical system (not shown), an optical image of the reflected light that irradiated the document or a scanned image of the modulated laser beam is formed on the surface of the photoreceptor drum 1 as shown by arrow G, and the light hits the photosensitive drum 1. A latent image is formed by discharging the charge in the exposed area.

This latent image is made into a visible image by applying toner to the developing device B, and after being irradiated with a static elimination lamp 4 to weaken the charge on the surface of the photoreceptor drum 1, a paper 9 is brought into close contact with the photosensitive drum 1, and a toner image is formed by a transfer charger 5. is transferred onto paper 9.

Next, the paper 9 is transferred to the photosensitive drum 1 by the separation charger 6.
The image is separated from the paper 9, sent to a fixing device (not shown), and heated under pressure to fix the image on the paper 9.

The toner remaining on the photosensitive drum 1 is removed by a cleaning device 7, and the remaining charge is completely removed by a static elimination lamp 8, completing one cycle.

At this time, a high voltage of, for example, 6KV to 7KV is applied to each charger 2, 5.6 from a high-voltage power supply to generate a corona discharge, and this corona discharge charges or neutralizes the opposing member and also charges the developing device 3. For example, 2
A bias voltage of 00V to 600V is applied to charge the toner.

I try to obtain the optimum development conditions.

Since the power output supplied to each charger 2, 5.6 and developing device 3 must be stable at all times, the electrophotographic apparatus is equipped with various high voltage power supplies.

FIG. 1 is a circuit diagram showing a DC constant voltage high voltage power supply as a first embodiment equipped with a switching power supply device according to the present invention, and is composed of a control section A and a high voltage section B. In FIG.

The control unit A includes a microprocessor 10 that performs sequence control of not only the power supply but also the entire electrophotographic apparatus, a timer 11 that changes the duty ratio of the switching element according to the output of the microprocessor 10, a buffer 12 on the output side, and The microprocessor 10 performs overall sequence control, and is generally placed near the operating section.

On the other hand, the high voltage section B includes a conversion transformer 13, a primary winding of this conversion transformer 13, and a switching element FET (
a primary side circuit consisting of a field effect transistor) 14;
Secondary winding of conversion transformer 13 and diode 15. A rectifying and smoothing circuit which is an output circuit consisting of a capacitor and a voltage divider resistor 17.1 which is an output detection means for detecting the output voltage of the rectifying and smoothing circuit and feeding it back to the control section A.
8, and resistors 22 and 23 that divide the voltage of the drive signal of FET 14.
and resistance 24. It consists of a snubber circuit for absorbing surges consisting of a capacitor 25, and is generally arranged near each charger 2, 5.6 (FIG. 4) in order to shorten the high-voltage wiring.

A 24V DC power source and a 5V DC control power source are connected to the control unit A, and the 5V DC power source is connected to a microprocessor 10 with a built-in A/D converter and a timer 11 (
and a buffer 12), and the DC 24V is sent to the high voltage section B via the control section A, and is supplied to the series circuit of the primary winding of the conversion transformer 13 and the FET 14.

Between the control section A and the high voltage section B, there is a cable connecting a voltage divider consisting of resistors 17 and 18 and a variable resistor 20 to feed back the detection signal, a 24 V DC power supply line, a buffer 12 and a resistor 22. A drive signal line connecting the
Wire harness 2 consisting of common (C:OM) line
Connected by 1.

Next, the operation of this embodiment will be explained.

The FET 14 turns on and off the DC 24V current input to the primary winding of the conversion transformer 13, and the high voltage pulse obtained in the secondary winding is rectified and smoothed by the diode 15 and capacitor 16 to produce DC high voltage power. Output as .

This output voltage is stepped down by a voltage divider made up of resistors 17 and 18, and is fed back to the control section A via a cable as a detection signal.

The detection signal fed back to the control section A is transmitted to the variable resistor 2.
The voltage is further reduced by 0, and becomes below the maximum allowable input voltage of the A/D converter built into the microprocessor 10.

The microprocessor 10 inputs the step-down detection signal from the analog terminals AGND and AN and converts it into an A/D signal. In comparison, a control signal for controlling the on-duty ratio of the drive signal is output to the timer 11, which outputs an active signal for turning on and off the FET 14 at a constant switching frequency.

That is, a control signal is outputted to lower the on-duty ratio when the A/D converted data is larger than the target value, and to increase it when it is smaller.

Timer 1 transfers the drive signal according to the control signal to buffer 1.
2. It is output to the high voltage section B via the wire harness 21.

The high voltage part B is supplied to the series circuit of the primary winding of the conversion transformer 13 and the FET 14 by dividing the input active signal with a voltage divider consisting of resistors 22 and 23 and applying it to the base of the FET 14. Turns on/off the 24V DC current.

In this way, high voltage power stabilized at the reference voltage is output from the high voltage section B.

Since the maximum allowable voltage of the A/D converter built into the microprocessor 10 is less than 5V, the input voltage when outputting the reference voltage is set to 3V.

For example, the reference value of the developing bias voltage of the developing device 3 is 360
v, the output detection means in the conventional example is 1/
A detection signal whose voltage is stepped down to 120 is output.

According to this invention, the level of the detection signal can be set arbitrarily, but in this embodiment, for example, the resistance 17.
If the voltage division ratio of the voltage divider 18 is 1/10 and the level of the detection signal at the time of reference output is 36V, then the voltage division ratio of the variable resistor 20, which is the step-down means of the control section A, may be set to 1/12.

In the conventional example, when noise is added to the cable on a single day, it is directly input to the A/D converter, but in this example, the noise is suppressed to 1/12 by the variable resistor 20, so the noise margin is as much as 22 dB. If the level of the detection signal is further increased, the noise margin will be further improved.

FIG. 2 is a circuit diagram showing a high-voltage part C of a DC constant current high-voltage power supply as a second embodiment, and since the control part A is the same as the first embodiment shown in FIG. 1, illustration thereof is omitted. Further, the same parts as those in the first embodiment are given the same reference numerals, and the description thereof will be omitted.

In this embodiment, a dummy resistor 30 is provided in parallel to the output end of a rectifying and smoothing circuit which is the output circuit on the secondary side of the conversion transformer 13, and a current detection resistor 31 is connected in series to the ground (GND) side of the output end. A cable is connected to both ends of the resistor 31, and the rest of the configuration is as follows.
This is similar to the example.

With this configuration, the high voltage section B outputs high voltage power whose output current is stabilized at the reference current value.

Furthermore, the same effect as in the first embodiment can be obtained regarding the improvement of the noise margin.

FIG. 3 is a circuit diagram showing an AC stabilized high-voltage power supply as a third embodiment, and the same parts as in the first embodiment are given the same reference numerals and the explanation thereof will be omitted.

This embodiment is composed of a control section and a high voltage section E, and a timer 34 in the control section receives a voltage of less than 50% from the two output terminals OA and OB in response to a control signal output from the microprocessor 10. Instant signals A and B having equal duty ratios are output alternately at intervals of 172 switching cycles, and are passed through buffers 35A and 35B, respectively.
It is output to the high voltage section E via the wire harness 36.

The high voltage section E includes a primary winding L1, a secondary winding L2, and a tertiary winding L.
3, and two sets of switching elements each connected to the primary winding L1 of the NPN transformer 40.
type transistors QA, QB and their protection diodes 4
1A, 41B, resistors 42A, 45A and m resistor 42B,
45B and a diode 44 connected to the tertiary winding L3 of the conversion transformer 40. Capacitor 45.
It is composed of a rectifying and smoothing circuit including a dummy resistor 46.

Primary winding L1 with center tap of conversion transformer 40
A 24V DC power supply supplied via the control unit is connected to the center tap of the primary winding L1, and transistors QA and QB whose emitters are both connected to the common line are connected to both ends of the primary winding L1. The collectors of the transistors QA and QB are connected to each other, and protection diodes 41A and 41B are respectively connected between the emitters and collectors of the transistors QA and QB so as to bypass them when a reverse voltage is applied.

The perturbation signals A and B output from the control section are respectively input to the bases of the transistors QA and QB via a voltage divider, and the transistor Q is activated for a time corresponding to the duty ratio.
By alternately turning on A and QB, an alternating current flows through the primary winding L1.

As a result, the high-voltage AC induced in the secondary winding L2 of the conversion transformer 40 is output as is as an AC high-voltage power supply, and the
The alternating current induced in the next winding L3 is half-wave rectified by a rectifying and smoothing circuit serving as an output detecting means and converted into a direct current voltage, which is fed back as a detection signal to the control unit via the cable.

The detection signal input to the control unit is that of the first embodiment.

Similarly to the second embodiment, the voltage is stepped down and the microprocessor 1
Control is performed by inputting to the A/D converter of 0.

In this embodiment, instead of the output detection means directly detecting the high voltage alternating current output from the secondary winding 1iALz, the tertiary winding L3 is provided and the output is indirectly detected by the output of the tertiary winding L3.
Its controlling action and effect on noise etc. remain unchanged.

In FIG. 4, the DC constant voltage high voltage power supply shown in the first embodiment (FIG. 1) is used as a bias power supply for the developing device 3, for example, and the DC constant current high voltage power supply shown in the second embodiment (FIG. 2) For example, the AC stabilized high voltage power supply shown in the third embodiment (FIG. 3) can be used as a discharge power source for the separate charger 6, and
Each is provided near each part.

As explained above, according to the present invention, even if the output detection means provided in the high voltage section is located far from the control section, the output detection signal is sent at a large signal level to the input end of the control section. Since the voltage is stepped down immediately before input, there is no output ripple or abnormal oscillation caused by noise or other factors.

High-quality images can be obtained by stably controlling the output of the high-voltage power supply.

Further, by arranging the control section and the high voltage section at arbitrary positions, the electrophotographic apparatus can be made smaller.

Furthermore, it is possible to configure a safe system by arranging the high-voltage parts close to their respective loads, such as the chargers 2 and 5.8 or the developing device 3, and shortening the high-voltage wiring to prevent the generation of ozone. .

Moreover, since the voltage step-down means can be constructed from a variable resistor or a voltage divider, high-quality images can be obtained at the same cost and size as conventional ones.

The above embodiments have been described with respect to the case where the switching power supply device according to the present invention is applied to a high voltage power supply of an electrophotographic apparatus, but needless to say, other high voltage power supplies can be used.
It can also be applied to medium and low voltage power supplies.

Furthermore, in the case of a low voltage power supply, an amplifier may be provided in the output detection means and the detection signal may be set at a level higher than the output voltage.

〔Effect of the invention〕

As described above, according to the present invention, in a switching power supply device, the detection signal from the output detection means is not affected by noise, and the power output can be stably controlled.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a first embodiment of the invention, Fig. 2 is a circuit diagram showing main parts of a second embodiment of the invention, and Fig. 3 is a circuit diagram showing a third embodiment of the invention. , FIG. 4 is an explanatory diagram of the area around the photosensitive drum of an electrophotographic apparatus using the switching power supply device according to the present invention. 10...Microprocessor 11.34...Timer (10, 11:10,34...Effect means) 13.40
...Conversion transformer 14...FET (switching element) 15...Diode 16...Capacitor 17.18.31
...Resistor (output detection means) 19...Cable 20...Variable resistor (step-down means) 44...Diode 45...Capacitor 4th...Dummy resistor (44, 45, 46... Output detection means) A, D...
Control parts B, C, E...High voltage part QA, QB...Transistor (switching element) W
i2 Figure 1 and 4

Claims (1)

[Claims] 1. A series circuit consisting of a primary winding of a conversion transformer connected to a DC power supply and a switching element, and an AC power induced in the secondary winding of the conversion transformer as it is or after being rectified and smoothed. an output circuit that outputs the AC power or the DC power as DC power, an output detection means that detects the voltage or current of the AC power or the DC power output from the output circuit and outputs a detection signal, and the detection means that the output detection means outputs. A switching power supply device comprising a drive unit that stabilizes the AC power or the DC power by outputting a drive signal that turns on and off the switching element according to a signal, wherein the drive inputs the detection signal. A switching power supply device characterized in that a step-down means for stepping down the detection signal is provided immediately before an input terminal of the means.