JPH04125069A - Power source device - Google Patents

Abstract

PURPOSE:To reduce power loss and to reduce in size by driving the primary side of a transformer from a DC power by a switching element, and forming a resonance circuit which resonates with a driving frequency of the primary side by the secondary winding of the transformer and a capacitor. CONSTITUTION:A rectifying diode D2 is switched ON when a switching transistor Q1 of a primary side is cut OFF to rectify the output of a tertiary winding L3, a negative DC high voltage is output to the anode of the diode D2, and superposed on the AC output of a secondary winding L2. A load current of a charging roller is converted to a terminal voltage by a resistor R3, AC/DC- converted by a current detector 2, and compared with a reference value of a predetermined value by an error amplifier 3. The compared output is converted to a pulse width of a conducting time ratio responsive to the output by a PWM circuit 4, and the transistor Q1 of the primary side is driven by a predetermined frequency to be controlled so that a load current becomes a predetermined value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power supply device, and particularly to a power supply device used as a charging power supply for an image processing device.

[Conventional technology]

2. Description of the Related Art As a drive source for a contact charging roller or a blade in an electrophotographic copying machine, printer, or the like that is an image processing device, a power source in which a sine wave AC high voltage and a DC high voltage are superimposed is used.

In the conventional power supply device of this kind, as shown in FIG. 7, a system has been used in which the output of the sine wave generating circuit 1 is boosted by a step-up transformer T1 as a sine wave AC high voltage power source. In the figure,
Ll is a primary winding, and L2 is a secondary winding.

[Problem to be solved by the invention]

However, since the sine wave AC high voltage power supply of the conventional power supply device cannot be driven by switching, power loss is large, and countermeasures for increasing the temperature of the drive circuit are required. In addition, the circuit becomes complicated due to push-pull or complementary driving. Furthermore, the sine wave generating circuit itself requires a larger number of elements than a rectangular wave generating circuit, and also requires a larger number of elements that require a greater degree of variation, resulting in higher costs.

The present invention has been made in order to solve the problems of the conventional example as described above, and aims to provide a power supply device that has less power loss and can be miniaturized.

(Means for Solving the Problem) Therefore, in the present invention, a transformer is formed of a transformer that drives a switching element on the primary side from DC power to boost the voltage, a secondary winding of the transformer, and a capacitor, a resonant circuit that resonates with the drive frequency of the primary side and supplies a sine wave voltage to the load, detects the current flowing to the load,
The power supply device is characterized in that the load current is controlled by changing the energization time ratio of the switching element at a predetermined rate.

The present invention is characterized in that the transformer is an iron resonant transformer, and the capacitor is a load capacitor.

Further, the transformer is provided with a tertiary winding closely coupled to the primary side, and the output of the tertiary winding is a DC output that is rectified when the switching element driven on the primary side is cut off. Features.

The transformer is characterized in that it is provided with a reset winding having a number of turns several times the number of turns of the primary winding.

The transformer is characterized in that a resistor of 100Ω to 10MΩ is provided in the secondary winding in series with the capacitor.

The transformer is characterized by having a choke coil installed in the secondary winding in series with the capacitor.

Further, the power source is characterized in that it includes each of the transformer and the resonant circuit, detects the amplitude of the sine wave voltage of the resonant circuit, and controls the detected output by changing the energization time ratio of the switching element in a predetermined manner. It shall be a device.

The invention also includes the resonant circuit and the tertiary winding, and connects the resonant circuit and the tertiary winding to bring the DC output of the tertiary winding into contact with the sine wave voltage of the resonant circuit. The power supply device is characterized in that it is superimposed as a DC bias for charging.

The tertiary winding is characterized in that the rectified DC output of the tertiary winding is connected to a load as a developing bias for applying to the developing sleeve.

Alternatively, the tertiary winding is characterized in that the rectified DC output of the tertiary winding is connected to a load as a transfer bias for application to a transfer roller, thereby attempting to achieve the above object.

[Effect]

The primary side of the transformer is driven by a switching element from DC power, and the secondary winding of the transformer and a capacitor form a resonant circuit that resonates with the driving frequency of the primary side, supplying a sine wave voltage to the load. Also, at this time, the current flowing through the load is detected and controlled by changing the energization time ratio of the switching element so that it becomes a predetermined value.

Note that the transformer is an iron resonant transformer, and a resonant circuit can be formed with the capacitance of the load without the need to add a special capacitor.

Furthermore, the tertiary winding provided in the transformer can be used as a DC output power source that rectifies this induced voltage.

A reset winding provided on the primary side of the transformer causes the reset diode to conduct quickly after the switching element is cut off, thereby boosting the collector output of the switching element from the supply voltage.

A predetermined resistor or a choke coil in series with a capacitor provided in the secondary winding of the transformer enables waveform shaping of the sine wave.

The power supply device according to the present invention constituted by the transformer and the resonant circuit can detect the amplitude of the resonant circuit output and control the output to a predetermined value.

Further, this DC output is superimposed on a sine wave voltage and serves as a DC bias for contact charging in a copying machine, etc., and the DC output serves as a DC bias for development or a transfer bias for a transfer roller.

〔Example〕

The present invention will be explained below based on examples.

(Example 1) Figure 1 is a circuit diagram of Example 1 according to the present invention, and Figure 2 is a circuit diagram of Example 1 according to the present invention.
FIG. 3 is a voltage waveform diagram of each part in Example 1 shown in the figure. Note that the same (equivalent) components as in the conventional example shown in FIG. 7 are represented by the same reference numerals.

In the figure, T1 is a ferro-resonant transformer, L
la is the primary winding, Llb is its reset winding, which has approximately 3 to 10 times the number of turns as the primary winding Lla, and L2 is a high voltage winding with a step-up ratio of approximately 50 to 200 times that of the secondary winding. The magnetic coupling between the 51st windings Lla and Llb is loosened by a gap.

L3 is a tertiary winding closely coupled to the primary windings Lla and Llb. Ql is a switching transistor which is a switching element that controls on/off the DC power input on the primary side of the transformer T1, C2 is a capacitor connected in parallel to the secondary winding L2 of the transformer T1, and C3 is a charging roller load. A load capacitor, 2 is a current detection circuit that detects the load current, 3 is an error amplifier that compares the load current with a predetermined value of the reference power supply 5, and 4 is a PWM (PWM) that receives the output of the error amplifier 3 and controls the switching transistor Q1. This is a pulse width modulation (pulse width modulation) circuit. In addition, Dl is a reset diode,
D2 is a rectifier diode that is a rectifying element that rectifies the induced voltage of the tertiary winding Lla, Pl is an output terminal, A is a resonant circuit,
B is a DC output circuit.

Next, the operation will be explained.

Figure 2 shows voltage waveforms at various parts. (a) is PWM circuit 4
(b) is the collector output waveform of switching transistor Q1, (C) is the output waveform of tertiary winding iL3,
(d) is the output waveform at the output terminal P1.

When the switching transistor Q1 on the primary side is cut off, the rectifier diode D2 is made conductive to rectify the output of the tertiary winding shown in FIG. extracts high DC voltage. This DC high voltage is connected to the secondary winding 1QL2 and the secondary winding L
This is superimposed on the AC output of No. 2, resulting in an output with a voltage waveform shown in FIG. 2(d).

The transformer T1 is configured to form a resonant circuit with the primary drive frequency as the center frequency, with the inductance of the secondary winding fiL2, the capacitance of a parallel capacitor consisting of the capacitor C2, and the load capacitance C3 of the charging roller. It is configured.

Therefore, a sinusoidal AC high voltage output is obtained from both ends of the secondary winding L2. The reset winding Llb causes the reset diode D1 to conduct quickly after the switching transistor Q1 is turned off. Therefore, the collector output of the switching transistor Q1 has a voltage approximately twice that of the input terminal Vcc, as shown in FIG. 2(b). Secondary winding L
The output of No. 2 is supplied to the charging roller via the output terminal P1.

Further, the load current of the charging roller is converted into a terminal voltage by a resistor R3, AC-DC converted by a current detection circuit 2, and compared with a reference value which is a predetermined value by an error amplifier 3. This comparison output is converted by the PWM circuit 4 into a pulse width having a current-carrying time ratio according to the output, and the primary side switching transistor Q
1 is driven and controlled at a predetermined frequency. In Figure 2(a),
The output waveform of the PWM circuit 4 that drives this switching transistor Q1 is shown.

(Embodiment 2) FIG. 3 shows a circuit diagram of Embodiment 2 according to the present invention. In addition,
Components that are the same (equivalent) to those of the conventional example shown in FIG. 7 and the first embodiment shown in FIGS.

In FIG. 3, L4 is a detection winding of transformer T1, and 6 is an amplitude detection circuit for detecting the amplitude of voltage. In place of the current detection circuit 2 in the circuit diagram of Embodiment 1 shown in FIG. 1, a detection winding L4 closely coupled to the secondary winding L2 of the transformer T1 is provided, and an output corresponding to the output amplitude of the secondary winding L2 is provided. The amplitude detection circuit 6
After that, the switching transistor Q1 was controlled in the same manner as in Example 1 to stabilize the output amplitude.

Furthermore, an additional capacitor C2 shown in FIG.
is omitted, and the load capacity C3 of the charging roller and the secondary winding L2 are
This is a power supply device in which a resonant circuit A is formed by If the load capacitance C3 is used as the cotensor of the resonant circuit A in this way,
It can be made smaller by omitting parts.

(Embodiment 3) FIG. 4 is a circuit diagram of Embodiment 3. In the figure, the rectified output of the tertiary winding of the transformer T1 is branched into three branches, each of which is provided with series regulators 7a to 7C, and these are supplied as the developing DC)<earth, transfer bias, and charging DC bias of the copying machine. , and other circuits are the same as those in the second embodiment.

(Embodiment 4) FIG. 5 is a circuit diagram of Embodiment 4. Embodiment 4 is a power supply device in which a resistor R4 is inserted in series with the secondary winding L2 constituting the resonant circuit A of the transformer T1 in order to improve the waveform shaping of a sinusoidal high voltage. Since the other circuits are substantially the same as those in the first embodiment shown in FIG. 1, their explanation will be omitted.

(Example 5) FIG. 6 is a circuit diagram of Example 5. Example 5 is Example 4
This is a power supply device in which a choke coil L5 is inserted in series with the secondary winding L2 constituting the resonant circuit A of the transformer T1 for the same purpose.

〔Effect of the invention〕

As explained above, according to the present invention, the primary side of the transformer is driven by DC power using a switching element, a resonant circuit that resonates with the driving frequency of the primary side is formed in the secondary winding of the transformer, and the load Since the configuration was configured to supply a sine wave voltage to
It can be driven with one switching element, has little power loss, and does not require countermeasures against temperature rise in the slave drive circuit.

Note that if the transformer is an iron resonant transformer and the load capacitance is used as the capacitor of the resonant circuit, an efficient power supply device can be formed with fewer parts.

Further, by providing a tertiary winding, a DC voltage can also be generated along with a sinusoidal voltage in the same transformer.

Since a reset winding is provided on the primary winding of the transformer, boosting efficiency can be increased, and a series resistor or choke coil can be inserted into the resonant circuit of the secondary winding to adjust the waveform of the sine wave voltage. can.

Further, the output voltage can also be controlled by detecting the amplitude of the output voltage in addition to the load current, and changing the energization time ratio of the switching element.

In addition, a power supply device that can superimpose a DC output on the sine wave voltage of a resonant circuit and use it as a DC bias for contact charging in a copying machine, for example, or supply DC output from a single transformer for applying DC output to a developing sleeve and a transfer roller. It can be done.

As described above, it is possible to provide a power supply device that has less power loss and can be downsized.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of Embodiment 1 according to the present invention, and FIG. 2 is a circuit diagram of Embodiment 1 of the present invention.
3 is a circuit diagram of Embodiment 2 according to the present invention, FIG. 4 is a circuit diagram of Embodiment 3, FIG. 5 is a circuit diagram of Embodiment 4, FIG. 6 is a circuit diagram of the fifth embodiment, and FIG. 7 is a circuit diagram of a sine wave AC high voltage power supply in a conventional power supply device. Note that in each figure, the same reference numerals indicate the same (equivalent) components. T 1------- Transformer L 1--------Primary winding L 2--------Secondary winding L3=-Tertiary winding Llb-...Reset winding C2 , C3 --- Capacitor A --- Resonant circuit B --- DC output circuit 2 --- Current detection circuit 6 --- Amplitude detection circuit R4 ---・-Resistor L 5--Choke coil

Claims (10)

[Claims] (1) A transformer that drives a switching element on the primary side from DC power to step up the voltage, a secondary winding of the transformer, and a capacitor. a resonant circuit that supplies a wave voltage, detects a current flowing through the load, and controls the load current to a predetermined value by changing the energization time ratio of the switching element. (2) The power supply device according to claim 1, wherein the transformer is an iron resonant transformer, and the capacitor is a load capacitance. (3) The transformer is provided with a tertiary winding closely coupled to the primary side, and the output of this tertiary winding is a DC output that is rectified when the switching element driven by the primary side is cut off. The power supply device according to claim 1. (4) The power supply device according to claim 1, wherein the transformer is provided with a reset winding having a number of turns several times the number of turns of the primary winding. (5) The transformer has a capacitor connected in series with the secondary winding.
2. The power supply device according to claim 1, further comprising a resistor of 00KΩ to 10MΩ. (6) The power supply device according to claim 1, wherein the transformer is provided with a choke coil in series with the capacitor in the secondary winding. (7) Each of the transformer and resonant circuit described in item 1 is provided, the amplitude of the sine wave voltage of the resonant circuit is detected, and the detected output is controlled to a predetermined value by changing the energization time ratio of the switching element. Features a power supply device. (8) The resonant circuit described in item 1 and the tertiary winding described in item 3 are provided, and the resonant circuit and the tertiary winding are connected, and the sine wave voltage of the resonant circuit is applied to the tertiary winding. A power supply device characterized in that a DC output of a tertiary winding is superimposed as a DC bias for contact charging. (9) The power supply device according to claim 3, wherein the tertiary winding connects the rectified DC output of the tertiary winding to a load as a developing bias for applying to the developing sleeve. (10) The power supply device according to claim 3, wherein the tertiary winding connects the rectified DC output of the tertiary winding to a load as a transfer bias for application to a transfer roller.