JPH0379952B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an inverter type multi-output power supply used in a power supply for an electronic copying machine and the like.

Prior Art A conventional inverter-type multi-output power supply is constructed as shown in FIG. That is, two inverters 2 and 3 are connected in parallel to input terminals 1 and 1', transformers 4 and 5 are connected to these inverters 2 and 3, respectively, and a rectifier circuit 6 is connected to the output side of one transformer 4. The output side of the other transformer 5 was configured to obtain a DC output, and an AC output from the output side of the other transformer 5.

With this configuration, you can turn on AC output while getting DC output.
When it is desired to turn off the inverter 3, the purpose can be achieved by turning on and off the inverter 3.

However, as mentioned above, two inverters 2,
This requires two transformers 4 and 5, which is extremely disadvantageous in terms of cost.

Therefore, as shown in FIG. 2, one inverter 8 is connected to the input terminals 7 and 7', one transformer 9 is connected to this inverter 8, and one output winding of this transformer 9 is A configuration has been developed in which a rectifier circuit 10 is connected to the wire 9a to obtain a DC output, and a reed relay 11 is connected to the other output winding 9b of the transformer 9 to obtain an AC output.

The same purpose can be achieved by using a bidirectional three-terminal thyristor instead of the reed relay 11.

Problems to be Solved by the Invention However, when the reed relay 11 is used, it cannot be turned on and off frequently and lacks reliability, and the reed relay 11 itself is expensive and disadvantageous in terms of cost.

Also, if a bidirectional three-terminal thyristor is used,
There was a problem where the AC output could no longer be used if it was a high voltage output.

The present invention aims to eliminate the above-mentioned conventional drawbacks, and provides an inverter-type multi-output power supply that has a simple configuration, can withstand high voltage output, is highly reliable, and is advantageous in terms of cost. be.

Means for Solving the Problems In order to solve the above problems, the present invention has at least a first winding wire and a second winding wire wound around a primary side magnetic circuit, and a second winding wire wound around a secondary side magnetic circuit. a leakage transformer having at least a third winding;
A parallel resonant circuit formed by the resonant capacitor of the third winding, a switching element connected in series to the DC input and the first winding, and a constant frequency that matches the resonant frequency of the parallel resonant circuit. a pulse generation circuit that provides a duty cycle pulse as an input signal to the switching element;
A first mode in which the duty cycle of the pulse is set to a range that is greater than or equal to the minimum duty cycle and less than or equal to the resonance start duty cycle of the parallel resonant circuit; A switching circuit for switching the duty cycle of two modes, and a rectifier circuit connected to the second winding to obtain a first DC output and a second output from the third winding. It is composed of

Effects The above configuration provides stable operation, low cost, and simple configuration.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to FIGS. 3 to 9 of the drawings.

First, in Fig. 3, 12 and 12' are input terminals, and this input terminal 12 is the leakage transformer 1.
3 is connected to the intermediate tap of the primary winding _N1 , and both ends of this primary winding _N1 are connected to the collectors of switching transistors 14, 14' used as switching elements. The emitters of the switching transistors 14, 14' are grounded, and the emitters of the switching transistors 14, 14' are grounded.
A pulse generating circuit 15 is connected to the bases of 4 and 14'. This switching transistor 1
4, 14' and the pulse generating circuit 15 constitute an inverter.

Note that a DC input is applied between the input terminal 12 and the input terminal 12' (ground level).

Further, a rectifier circuit 16 consisting of a diode and a capacitor is connected to the second winding of the leakage transformer 13, that is, another winding _N2 on the primary side, and is configured to obtain a DC output, and the third winding, that is, the secondary winding A resonant capacitor 17 is connected to the winding _N3 .
It is configured to obtain AC output.

In addition, the resonant capacitor 17 is connected between the terminals N ₃₁ and N ₃₂ of the secondary winding _{N 3} and is a resonant winding that constitutes a parallel resonant circuit, and _the second output ( This is the third winding (secondary winding N ₃ ) for obtaining AC output).

In this embodiment, the resonant winding and the third winding share a part (N ₃₁ to N ₃₂ ), but even if both share all of N ₃₁ to _{N 32} , Completely separate windings may also be used.

Note that by connecting the resonant capacitor 17 to the secondary winding _N3 , the leakage transformer 13 constitutes an iron resonant transformer.

FIG. 9 is a sectional view of the leakage transformer and explains its details.

40 is an iron core that constitutes the main magnetic circuit, and 41
is a shunt pass iron core provided between the primary side and the secondary side, which generates leakage magnetic flux between the primary and secondary sides and provides loose coupling between the primary and secondary sides.

A first winding N ₁ and a second winding N ₂ are wound around the shunt pass iron core in the primary magnetic circuit, and a third winding N ₃ is wound in the secondary magnetic circuit. There is. Further, 42 is a bobbin for winding the winding wire.

In the above configuration, FIGS. 5a and 5b are on/off timing charts of the switching transistors 14, 14', with a high level being on and a low level being off. FIG. 5a shows the operation of the switching transistor 14, and FIG. 5b shows the operation of the switching transistor 14'. in this case,
The duty cycle δ is assumed to be δ=T _ON /T.

When the duty cycle δ is changed in FIG. 3, the AC output voltage changes as shown in FIG. 4. In FIG. 4, C is a case where the leakage transformer 13 is a general transformer in which the leakage transformer 13 is not of the leakage type and the resonant capacitor 17 is not connected, and the relationship between the duty cycle δ and the AC output voltage is directly proportional. The leakage transformer 13 is of a ferro-resonant type, and the resonance frequency of the ferro-resonant transformer is determined by the inductance between the resonance windings N ₃₁ and _{N 32} wound around the secondary side magnetic circuit of the leakage transformer 13 and the resonance capacitor 17. When the resonance frequency and the oscillation frequency of the inverter are set to the same value, the duty cycle δ-AC output voltage curve becomes as shown in a. When the duty cycle δ is small, the on time of the switching transistors 14 and 14' is not sufficient for the resonance period, so the ferro-resonant transformer does not resonate.
Almost no voltage appears on the AC output. However, when the resonance start duty cycle δ _s is exceeded, the output voltage begins to rise (in general, in a ferro-resonant transformer, as the input voltage increases, after a certain point, the output voltage decreases in the input voltage range below that point). (The boundary is called the resonance starting point) and the duty cycle is δ _s.
In the range of ~40%, the output increases almost linearly with respect to the duty cycle. and,
When the day-to-day cycle reaches 40% to 50%, the on-time T _ON of the applied pulse almost matches the half period of the resonant frequency of the ferro-resonant transformer, resulting in a complete resonant state. δ
Even if you increase , the AC output voltage will not increase that much.

By keeping the duty cycle below the resonance start duty cycle in this way, it is possible to realize an extremely small range of AC output voltage.

FIG. 4b shows a curve when the resonant frequency of the iron resonant transformer and the oscillation frequency of the inverter are slightly different. In this case as well, it is possible to realize a region where the AC output voltage is extremely small. However, the resonance start duty cycle δ _s ′
Since δ s is lower than the above-mentioned δ _s , the range of its duty cycle is necessarily small.

On the other hand, the second winding N ₂ wound around the primary magnetic circuit of the leakage transformer 13 is not affected by the resonance of the loosely coupled secondary magnetic circuit, so the switching transistors 14 and 14 are not affected by the resonance of the loosely coupled secondary magnetic circuit. The voltage of the first winding N ₁ which is pulse-driven with ′, and the voltage of the second winding N ₂ to obtain a DC output becomes a square wave.
Since the DC output is rectified by the rectifier circuit 16, the square wave output is rectified by the switching transistors 14 and 1.
4' remains constant regardless of the on-time and the duty cycle δ. In other words, the DC output is the terminal voltage of the capacitor of the rectifier circuit 16, and if the forward voltage drop of the diode is ignored, this capacitor will be charged with the peak voltage generated in the second winding _N2 . Therefore, even if the duty cycle δ changes, the peak voltage does not change, and the DC output remains constant regardless of the duty cycle. However, if it becomes smaller than a certain limit (δ = 0 to δ ₀ ), the DC
The output voltage drops rapidly.

The reason why the DC output voltage suddenly decreases is that the switching transistors 14 and 14' have a turn-off delay due to a certain amount of accumulation time, so it is impossible to make the on time less than a certain pulse width. If you try to set the pulse width to , the duty cycle will become 0. The duty cycle δ ₀ determined by this minimum pulse width will be referred to as the minimum duty cycle.

Utilizing the characteristics of the duty cycle δ of the ferro-resonant transformer and switching transistor as described above, the duty cycle δ can be set from the minimum duty cycle δ ₀ to the resonance start duty cycle δ _s. This makes it possible to create a mode in which the output voltage of the AC output is greatly reduced, while the output voltage of the DC output remains almost the same as normal. This resonance start duty cycle δ _s is determined by the Q of the resonant circuit, the resonant frequency of the ferro-resonant transformer, and the ON/OFF state of the switching transistor.
It can be set to some extent by the off frequency ratio.

FIG. 7 shows a circuit diagram of an example in which the inverter type multi-output power supply of the present invention as described above is used as a power supply for an electronic copying machine. One of the input terminals 12 is connected to the intermediate tap of the primary winding _N1 of the leakage transformer 13, and both ends of this primary winding _N1 are connected to the collectors of the switching transistors 14, 14'.
The emitters of the switching transistors 14, 14' are grounded, and the bases are connected to a steering circuit 18, to which a pulse width modulator 19 is connected. A pulse generation circuit 15 that generates a signal is connected. The steering circuit 18 outputs one of the outputs of the pulse width modulator 19.
It functions to convert phase signals into two-phase signals as shown in FIG. 5a and b.

A rectifier diode 20 is connected to one end of the separate winding _N2 of the primary magnetic circuit of the leakage transformer 13.
A circuit consisting of a rectifying filter capacitor 21, a resistor 22, and a constant voltage element 23 is connected, and the end thereof is
It is designed to obtain DC output 1. Further, the resistor 22 and the constant voltage element 23 constitute a simple regulator.

The method of obtaining DC output 1 in Figure 7 is a little unusual; usually, as shown in Figure 8, the separate winding _N2 of the primary magnetic circuit is completely separated from the primary winding N1, and the separate winding _N2 is completely separated from the primary winding N1.
This is obtained by rectifying both ends of N ₂ with a diode 20 and a filter capacitor 21. However, in the circuit shown in Figure 7, especially the DC output 1
Since there is no need to insulate or float between the magnetic circuit and the ground, the connection lead wires of the windings (N ₁ , N ₂ ) wound around the primary side magnetic circuit can be omitted as much as possible (in this case, one wire is omitted). This is why we have made this irregular connection.

Furthermore, a voltage detection winding _N4 is provided in the secondary side magnetic circuit of the leakage transformer shown in FIG.
Then, as shown in Figure 7, this voltage detection winding
A diode bridge circuit 24 and a capacitor 25 are connected to _N4 to convert the detected voltage into DC, and the detected voltage is divided by a variable resistor 26, and the voltage dividing ratio is further varied. 27 is the power supply for obtaining the reference voltage; 28
is an error amplifier, 29 to 32 are resistors, and resistors 29 to 32 are resistors.
31 divides the reference voltage. 33 is a transistor which functions as a switching element. 32 is the base resistance of this transistor 33, and 34 is the base resistance of this transistor 33.
AC output on/off control input terminal. Also,
35 is an on/off control input terminal of the pulse width modulator 19.

Further, a secondary winding N3 is provided on the secondary side of the leakage transformer 13, a resonant capacitor ₁₇ is connected to this secondary winding _N3 , the transformer is made into an iron resonant transformer, and this secondary winding N3 is connected to the secondary winding N3. ₃ is configured to obtain AC output at both ends.

With the above configuration, the DC output stably produces several hundred volts and is used as a developing bias in a copying machine as a load. This DC output is obtained by rectifying the primary side, so if the input voltage is constant, a constant output can be produced regardless of the duty cycle δ of the switching transistors 14 and 14'. , proportionally due to input voltage variations.
Since the voltage of the DC output also fluctuates, a resistor 22 and a constant voltage element 23 constituting a simple regulator are provided to keep the voltage of the DC output constant.

Assuming that the pulse width modulator 19 has a configuration in which the pulse width increases when the voltage of the control inputs d and f of the pulse width modulator 19 is increased, and the pulse is stopped when the voltage of the control input c is decreased, the on/off DC by lowering the input level of control input 35.
Both output and AC output stop, and when the input level is raised, DC output and AC output become operational. d
is the output of the error amplifier 28, which constitutes a feedback loop, and f is the input for regulating the maximum limit of the pulse width, which is normally used in switching regulators to prevent magnetic saturation of the transformer. Functionality is essential. The maximum limit value of this pulse width must be set slightly larger than the duty cycle δ in the usage range. Resistors 29 and 30 are used to make the settings.

When a high level input is applied to the AC output on/off control input terminal 34, the transistor 33
turns on, and the voltage at f decreases. At this time,
Since the voltage can be freely set by the resistor 31, the duty cycle δ at that time can be freely set.

In the case of this embodiment, the duty cycle δ when the transistor 33 is turned on is set to the minimum duty cycle δ ₀ to the resonance start duty cycle δ _s (actually measured values are 2% to 15%). It was appropriate. When the duty cycle δ is in the range δ ₀ to δ _s , the voltage of the DC output is unchanged from the normal duty cycle δ, that is, when the duty cycle is δ _s or more, whereas for the AC output, the voltage is
It is possible to create a mode in which the output voltage of KV drops to several hundred volts. Since the AC output load is a corona discharger, corona discharge cannot occur at a voltage of several hundred volts, and the adsorption effect of paper dust and toner to the corona discharger is also negligible, so it virtually stops as a load. It is possible to create a state of

In this way, the AC output can be turned on and off without changing the voltage of the DC output by inputting the AC output on/off control input terminal 34.

FIG. 8 shows an example of use in a power source for another copying machine, in which the ferro-resonant transformer is driven by a single drive, whereas in FIG. 7 the drive is push-pull.
Therefore, the steering circuit 18 is unnecessary.
In addition, in Figure 7, the same winding as the primary winding _N1 was used to obtain DC output, but a different winding
With _N2 , the DC output is in a floating state.

The AC output is an AC constant voltage output in Fig. 7, whereas in Fig. 8, a rectifier circuit consisting of a diode 36 and a capacitor 37 is provided in the secondary winding _N3 to obtain a DC constant current output. ing. Further, although the variable resistor 26 is used for detecting the output voltage in FIG. 7, it is used for detecting the output current in FIG. 38 is a transistor, 39 is a base resistor, and FIG. 8 shows that when the pulse width modulator 19 does not have a pulse stop input c, the maximum value is set to 0% by turning on the transistor 38 using the pulse width maximum limit input. It is configured so that both DC output and AC output are turned off.

Effects of the Invention As described above, the inverter type multi-output power supply of the present invention can obtain two outputs with one transformer and one inverter circuit, and one output can be turned on and off. When a load does not require a complete off state, it essentially has the functions of two transformers and two inverter circuits, resulting in a significant cost reduction. Furthermore, when the output to be turned on or off is a high voltage, a reed relay is not required, which not only improves reliability but also provides an advantage in terms of cost. Furthermore, when turning one output on and off, all that is required for on/off control is a pulse width signal.
It can be controlled with small current, low voltage, and low power, and there is no cost for the on/off drive circuit. In addition, since it uses a ferro-resonant transformer,
AC output can be obtained with low distortion, and of course,
DC output can also be obtained.

[Brief explanation of drawings]

1 and 2 are electrical circuit diagrams showing a conventional inverter-type multi-output power supply, FIG. 3 is an electrical circuit diagram showing an embodiment of the inverter-type multi-output power supply of the present invention, and FIG. 4 is an electrical circuit diagram showing the same. A characteristic diagram showing the relationship between the AC output of the power supply and the duty cycle δ, Figures 5a and b are timing charts showing the on/off operation of the switching transistor, and Figure 6 shows the DC output and duty cycle of the same power supply. FIGS. 7 and 8 are electrical circuit diagrams showing examples of use of the power supply, and FIG. 9 is a sectional view showing the structure of a leakage transformer. 12, 12'... Input terminal, 13... Leakage transformer, 14, 14'... Switching transistor, 15... Pulse generation circuit, 16... Rectifier circuit, 17... Resonant capacitor, N ₁ ... Primary winding wire, N ₂ ... separate winding, N ₃ ... secondary winding.

Claims (1)

[Claims] 1. A leakage transformer having at least a first winding and a second winding wound around a primary magnetic circuit and at least a third winding wound around a secondary magnetic circuit; A parallel resonant circuit consisting of a winding and a resonant capacitor, a switching element connected in series to the DC input and the first winding, and a duty cycle that can be controlled at a constant frequency matching the resonant frequency of the parallel resonant circuit. a pulse generation circuit that provides cycle pulses as input signals to the switching element, and a duty cycle of the pulses set in a range that is greater than or equal to the minimum duty cycle and less than or equal to the resonance start duty cycle of the parallel resonant circuit. A switching circuit that switches the duty cycle of a first mode and a second mode that operates at a frequency equal to or higher than the resonance start duty cycle, and a rectifier circuit connected to the second winding to generate a first DC output. and a second output from the third winding.