JP2705097B2 - AC power supply - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC corona generator required for a static elimination and separation process, which is one of electrophotographic image forming processes, such as an electronic copying machine and a laser beam printer, and an electric motor. Output frequency of uninterruptible power supply etc. is several K from commercial frequency of 50Hz / 60Hz
The present invention relates to an AC power supply that requires a low-frequency AC power supply of Hz.

Conventional technology As a means for supplying AC power, the conventional technology includes:
For example, there is a voltage resonance type DC-AC inverter as disclosed in Japanese Patent Publication No. 62-16078. FIG. 14 shows a circuit diagram of the above-described voltage resonance type DC-AC inverter, and FIG. 15 shows operation waveforms of the respective parts. In FIG. 14, a DC power supply 14 is connected between the power supply terminals 12 and 13, and one power supply terminal 12 is connected to an intermediate tap of the primary winding of the transformer 1 via a primary winding of an inductance 5 having a reset winding. Connect to A resonance capacitor 11 is connected between both ends of the primary winding of the transformer 1 and commonly connected to the other power supply terminal 13 via the collector-emitters of a pair of switching transistors 2 and 3. A pulse signal having a constant frequency and a variable pulse width is supplied from the pulse width control oscillator 4 to the base of the power supply, and alternately turned on. One end of the secondary winding of the inductance 5 is connected in series with the diode 6 in the forward direction to one power supply. The other end is connected to the other power supply terminal 13. The transformer 1 is provided with an appropriate gap to adjust the inductance so that the resonance frequency in combination with the resonance capacitor 11 matches the oscillation frequency of the pulse width control oscillator 4. With the above configuration, the transistors 2 and 3 are alternately turned on by the output pulse of the pulse width control oscillator 4, so that a sine wave AC voltage can be obtained in the secondary winding of the transformer 1.

The pulse width control oscillator 4 comprises an oscillation circuit 43, a pulse width modulation circuit 42, and a distribution circuit 41, as shown in FIG. Control. When this controlled output pulse, for example, a rectangular pulse as shown in FIGS. 15a and 15c is applied to the bases of the transistors 2 and 3, the collector voltages of the transistors 2 and 3 are respectively shown in FIGS. 15b and 15d. To change. That is, while the transistors 2 and 3 are off, the current of the primary winding of the inductance 5 is cut off, and an excessive voltage is likely to be induced at both ends of the winding and at the collectors of the transistors 2 and 3. However, the inductance 5 has a secondary winding, and Vid is induced at both ends of the winding. When the voltage Vid exceeds the voltage Vdc of the DC power supply 14, the energy is regenerated to the DC power supply 14 through the diode 6, The peak value of the collector voltage of the transistors 2 and 3 is limited to a constant value. By changing the pulse width of the output of the pulse width control oscillator 4, the transformer 1
The output voltage Vac of the sine wave obtained in the secondary winding can be arbitrarily varied.

However, in such a conventional configuration, resonance due to the inductance of the capacitor 11 and the transformer 1 is required, and a loss due to a resonance current and a DC resistance component of the inductance element occurs.
The dielectric loss of the capacitor 11 having a large capacitance required to secure a certain Q and resonate becomes large, and this loss is a factor that deteriorates the power supply efficiency. In order to stabilize a constant output waveform, it is necessary to stabilize the resonance frequency and improve the Q, adjust the core gap of the transformer 1 and adjust the capacitor 11 to tune the oscillation frequency and the resonance frequency. Because of the lack of productivity and the presence of a gap, the efficiency of the transformer 1 is poor, and the power supply efficiency tends to be further deteriorated. In addition, since it is necessary to tune, the output frequency cannot be easily changed, and the μ and equivalent gap of the core change due to changes in temperature and aging. There were drawbacks to bring. In addition, if the duty ratio changes to respond to changes in input and load,
When the duty ratio of the output pulse is small as shown in FIGS. 17a and 17b, the crest factor is high, and when the duty ratio of the output pulse is large as shown in FIGS. 17c and 17d, the crest factor is low. That is, there is a disadvantage that the output crest factor fluctuates greatly due to input fluctuation and load fluctuation.

When used as an AC power supply for electrophotography, there are generally two types of output waveforms: a sine wave type and a rectangular wave type. However, in the conventional method, only a sine wave type is used because resonance is used. There are drawbacks that cannot be addressed. Further, since the switching frequency of the transistor is as low as the output frequency, it cannot be increased in frequency, requires a very large inductance, and cannot be provided in a small size and at low cost.

Means for Solving the Problems In order to solve the above problems, the present invention relates to a high frequency pulse in which a switching element is connected to a primary winding of a transformer, and a duty ratio of each switching element is modulated in a trapezoidal wave with respect to time. And an inductance element having a regenerative diode and a reset winding inserted between the intermediate tap of the primary winding of the transformer and the DC input terminal, and an LC filter with a capacitance provided on the secondary winding of the transformer. The configuration is as follows.

Operation With the above configuration, the rising and falling slopes of the modulated trapezoidal wave can be adjusted to easily output an arbitrary waveform of a rectangular wave, a trapezoidal wave, a pseudo sine wave, and a triangular wave, and an output waveform of an arbitrary rising and falling slope. It can be provided with a circuit configuration, high efficiency, small size and low cost.

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

FIG. 1 shows a circuit configuration of an AC power supply device according to an embodiment of the present invention.

In FIG. 1, a DC power supply 14 is connected between the power supply terminals 12 and 13, and one power supply terminal 12 is connected to an intermediate tap of the primary winding of the transformer 1 through a primary winding of an inductance 5 having a reset winding. Connect to Then, the primary winding of the transformer 1 is connected to the other power supply terminal 13 through the collector-emitter of the pair of switching elements, the transistors 2 and 3, and the pulse width control oscillator 4 is connected to the base of the transistors 2 and 3 A high-frequency pulse whose ratio is trapezoidally modulated with respect to time is applied to turn on alternately, and the inductance 5
One end of the next winding is connected to one power supply terminal 12 via the diode 6 in series in the forward direction, and the other end is connected to the other power supply terminal 13. A capacitor 15 is equivalently added to both ends of the secondary winding of the transformer 1. It goes without saying that the switching element may be an FET or the like other than a transistor.

The pulse width control oscillator 4 includes a trapezoidal wave oscillation circuit 43, a high frequency oscillation circuit 45, a pulse width modulation circuit 4 as shown in FIG.
2, a distribution circuit 41, and as shown in FIG. 4a, a trapezoidal wave output of a trapezoidal wave oscillation circuit 43 and a high-frequency oscillation circuit.
The high-frequency output of 45 is obtained by a pulse width modulation circuit 42 composed of a comparator to obtain a high-frequency pulse whose time ratio is modulated by a trapezoidal wave as shown in FIG. High-frequency pulses shown in FIGS. 2a and 2b are obtained by sorting every half cycle.

The high frequency pulse is applied to the bases of the transistors 2 and 3, respectively, so that the transistors 2 and 3 are alternately turned on, and the high frequency component is removed by an LC filter including the inductance 5 and the equivalent capacitor 15 of the secondary winding of the transformer 1. 7c to 7f, the trapezoidal output voltage Vac can be obtained in the secondary winding of the transformer 1. The output voltage Vac can be arbitrarily varied and feedback controlled by varying the output amplitude of the trapezoidal wave oscillation circuit 43 of the high frequency pulse by the control signal 44.

FIG. 5 shows the trapezoidal wave oscillating circuit 43 of FIG. 3, which can vary the amplitude and arbitrarily vary the rising / falling slope of the trapezoidal wave.

The operation of the trapezoidal wave oscillation circuit shown in FIG. 5 will be described with reference to FIGS.

A charge ON / OFF current source 51 (hereinafter referred to as a charge current source) for charging the charge / discharge capacitor 53 is connected in series, and a discharge ON / OFF switch for discharging at both ends of the charge / discharge capacitor 53 is provided. OFF-capable current source 52 (hereinafter referred to as discharge current source)
Are connected in parallel, as shown in FIG.
The voltage across the charging / discharging capacitor 53 becomes the charging current source 51 at t1.
Is ON and the discharging current source 52 is OFF, it is charged with a constant current,
It rises linearly on the right. Next, at t2, the charging current source 51
Is turned off, and if the discharging current source 52 is kept off, neither charging nor discharging is performed, so that the parallel movement is performed while the voltage is maintained. Then, if the discharging current source 52 is turned on while the charging current source 51 is turned off at t3, the discharging is performed at a constant current, so that the voltage drops linearly downward to the right. At this time, if the current values of the charging current source 51 and the discharging current source 52 are the same, the gradient of t1-t2 and t3-t4 becomes the same. , A trapezoidal wave output is obtained. t2-t3
By changing the ratio between t1 and t2 or t3 and t4, the rising and falling of the trapezoidal wave output as shown in a-1 to a-4 of FIG.
Since the falling slope can be arbitrarily changed, that is, a rectangular wave, a trapezoidal wave, a pseudo sine wave, and a triangular wave, the output voltages shown in FIGS. 7c, d, e, and f can be obtained. If the current values of the charge / discharge current sources 51 and 52 are changed in an interlocking manner, the trapezoidal wave output can be varied in amplitude in a similar manner as shown in b-1 to b-3 in FIG. 7b. As a result, the output voltage has a similar waveform and the amplitude changes as shown in c-1 to c-3 in FIG. 7c. That is, a waveform having no change in waveform depending on the magnitude of the output amplitude is obtained.

FIG. 8 shows that the function as a filter is improved by connecting a capacitor 15 when the stray capacitance of the winding of the transformer 1 is small as the capacitor for the LC filter of the above-described embodiment. Although the filter capacitor 15 is connected to the secondary winding in the embodiment shown in FIG. 8, the same effect can be obtained by connecting it to the primary winding.

FIG. 9 shows the LC filter capacitor of the above-described embodiment, which utilizes the stray capacitance of the winding of the transformer 1.
As shown in FIG. 10, a foil-wound transformer having an increased opposing area between the windings and a stray capacitance is used.

FIG. 11 shows the case where a high-voltage generating transformer used for electrophotography or the like is used as the transformer 1 of the above-described embodiment, and the stray capacitance of the secondary winding of the transformer 1 is used as a capacitor for an LC filter. is there. In general, a high-voltage generating transformer boosts the voltage applied to the primary winding and outputs it as a high voltage to the secondary winding, so that the turns ratio between the primary winding and the secondary winding is set to a large value. Is the number of primary windings << the number of secondary windings. The stray capacitance of the secondary winding having a large number of turns is used as a capacitor for an LC filter.
Although the stray capacitance obtained in the embodiment shown in FIGS. 9 and 11 is not so large, the present invention can sufficiently obtain the effect as a filter even with a small stray capacitance since the switching frequency is high. FIG. 12 shows the voltage and current characteristics of an AC corona generator as a load for use as an AC power supply device for electrophotography, and FIGS. 13a, 13b, and 13c show the AC corona generator. A voltage waveform and a current waveform when each output waveform is applied will be described below with reference to the drawings. Generally, an AC corona generator is used in a charge removing and separating portion of an electrophotographic process, and it is necessary to increase a charge removing efficiency in order to improve a charge removing property of a photosensitive member and a separating performance of a photosensitive member and copy paper.
For that purpose, it is necessary to increase the effective corona discharge flow.
In FIG. 12, points a and b are the corona starting voltages on the plus side and the minus side, respectively. From point 0 onward, no current flows even if the voltage is increased. It has the characteristic that current starts to flow. However, the current flowing through the stray capacitance of the corona generator flows even if it does not exceed the points a and b. When the output voltage is a sine wave as shown in FIG.
Since the ratio of the time during which the half cycle of the waveform is equal to or higher than the corona start voltage is small (the conduction angle is small), a large effective corona discharge current cannot be obtained and the charge removal efficiency does not increase. In addition, when the output voltage is increased to increase the effective corona discharge current, it is necessary to strengthen the insulation and to increase the size of the transformer. When the output voltage is a rectangular wave as shown in Fig. 13b, the effective corona discharge current can be large, but the current flowing into the stray capacitance of the AC corona generator has a large peak value because its output waveform contains a high frequency component. . Although this peak current is a reactive current and does not contribute to the static elimination efficiency, the capacity of the switching element is required to be large, which is inefficient and cannot be provided at low cost. In addition, since the current flows in a spike shape, it causes noise and has a great possibility of affecting other circuits and devices. Further, since the rise and fall of the waveform are sharp, overshoot occurs in the output voltage. Because of this overshoot, the peak voltage becomes high, and it is necessary to strengthen the insulating relationship.

Therefore, the output voltage is set as a trapezoidal wave as shown in Fig. 13c, and the rising and falling slopes of the trapezoidal wave are arbitrarily varied to optimize the output peak voltage (insulation relation), effective current and noise generation respectively. It can be easily set, the simplification and downsizing of the corona generator and the simplification and downsizing of the power supply can be achieved, the charge elimination efficiency can be maximized, and the charge elimination performance and separation performance can be improved.

Effect of the Invention As described above, according to the present invention, a resonance circuit becomes unnecessary, the loss due to the DC resistance component of the resonance current and the inductance is reduced, and the dielectric loss is reduced because the resonance capacitor becomes a small-capacity filter capacitor. Is very small, so that high efficiency can be obtained.
In addition, it is not necessary to tune the transformer core gap adjustment and the resonance capacitor adjustment in order to obtain a stable output waveform, which is excellent in productivity and changes in the μ and equivalent gap of the transformer core due to temperature changes. The output waveform and output amplitude do not fluctuate. Further, since no core gap is required for the transformer, higher efficiency can be obtained.

The output frequency can be easily changed by adjusting the period of the trapezoidal wave output.

There is no change in the waveform and crest factor depending on the magnitude of the output amplitude, and a stable output waveform can be obtained.

Since resonance current does not flow through the transformer winding, the copper wire diameter of the winding can be reduced, and the transformer can be downsized, and a small switching element can be used.
High efficiency and low cost.

Since switching is performed at a high frequency, the L (inductance element) of the LC filter may be small, and C is inexpensive because stray capacitance can be used and becomes unnecessary.

It is possible to provide an AC power supply device that can set an arbitrary output waveform such as a rectangular wave, a trapezoidal wave, a pseudo sine wave, and a triangular wave, and that can also arbitrarily set the rising and falling slopes.

When used as an AC power supply for electrophotography, the rising and falling slopes of the trapezoidal wave can be set to the optimum points for the corona generator, the insulation of the power supply and the static elimination efficiency, and the peak current of the switching element can be reduced. A small size and high efficiency can be obtained, and the static elimination efficiency can be maximized, the static elimination and separation performance can be improved, and the size and noise of the corona generator and the power supply can be reduced.

The above effects can be obtained with a simple circuit configuration.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the AC power supply device of the present invention, FIGS. 2a and 2b are waveform diagrams illustrating the operation of the circuit shown in FIG. 1, and FIG. 3 is a diagram shown in FIG. FIG. 4 is a block diagram of the pulse width control oscillator, FIG. 4 is a waveform diagram illustrating the operation of the block shown in FIG. 3, FIG. 5 is a circuit diagram of the trapezoidal wave oscillation circuit shown in FIG. 3, and FIG. 7A and 7B are waveform diagrams for explaining a change in the operation of the block shown in FIG. 3, and c, d, e, and f are output waveform diagrams at the time of the change. FIG. 8 is a circuit diagram showing an application example of the present invention, FIG. 9 is a circuit diagram showing an application example of the present invention, and FIG. 10 is a perspective view showing a structure of a winding of the transformer shown in FIG. 11, FIG. 11 is a circuit diagram showing an application example of the present invention, FIG. 12 is a characteristic diagram of an AC corona generator for electrophotography, and FIGS. 13a to 13c are AC circuits for electrophotography in the application example shown in FIG. Negative corona generator FIG. 14 is a circuit diagram showing an example of a conventional voltage resonance type DC-AC inverter, and FIG. 15 is a circuit diagram showing an operation of the circuit shown in FIG. 14. The waveform diagram to be explained, FIG.
FIG. 17 is a block diagram of the pulse width control oscillator shown in FIG. 14, and FIGS. 17A to 17D are waveform diagrams comparing the operation of the circuit shown in FIG. 14 under different conditions. 1 ... Transformer, 2,3 ... Transistor, 4 ... Pulse width controlled oscillator, 5 ... Inductance, 6 ... Diode, 12,13 ... Power supply terminal, 14 ... DC power supply, 15 ... Capacitor.

Claims (5)

(57) [Claims] A pair of switching elements are connected in series to both ends of a primary winding of a transformer, and a DC power supply and a regenerative device are provided between an interconnection point of the pair of switching elements and an intermediate tap of the primary winding. An inductance element having a reset winding to which a diode is connected is connected in series, and a high-frequency pulse whose time ratio is modulated by a trapezoidal wave is alternately applied to the pair of switching elements every half cycle of the output cycle, and An AC power supply device in which a winding has a filter capacity. A pair of switching elements are connected in series to both ends of a primary winding of a transformer, and a DC power supply and a regenerative device are connected between an interconnection point of the pair of switching elements and an intermediate tap of the primary winding. A high frequency whose duty ratio is modulated by a trapezoidal wave obtained by connecting in series an inductance element having a reset winding to which a diode is connected and charging and discharging a capacitor with two constant current sources that can be turned on and off arbitrarily. An alternating-current power supply device in which a pulse is alternately applied to the pair of switching elements every half cycle of an output cycle, and a winding of the transformer has a filter capacity. 3. The AC power supply device according to claim 1, wherein a filter capacitor is connected to a winding of the transformer. 4. The AC power supply according to claim 1, wherein a stray capacitance of the winding of the transformer forms a filter capacitor. 5. The AC power supply according to claim 1, further comprising a high-voltage generating winding as a transformer.