JPH06197557A - Power conversion device - Google Patents

Abstract

PURPOSE:To obtain a power conversion device from which a high power factor can be obtained and, at the same time, which can be reduced in size and improved in economy by connecting a third diode between the output terminals of a full-wave rectifier circuit, with the anode of the diode being connected to the negative side of the output terminals. CONSTITUTION:In this converter, the center point t1 of the primary winding 24p of an output transformer 24 is connected to the positive side of the output terminals of a full-wave rectifier circuit 22 through a choke coil 23 and the terminals of the winding 24p are respectively connected to the negative side of the output terminals through switching elements 25 and 25. In addition, the positive side of the output terminals of the circuit 22 is connected to the anodes of diodes 30 and 31 and the cathode of a diode 32 through a choke coil 28 and smoothing capacitor 29 connected in series and the anode of the diode 32 is connected to the negative side. When the elements 25 and 26 are alternately turned on and off, a resonance voltage VS1 having a half sine wave-like waveform is generated in the turned-off section of the element 25 and another resonance voltage VS2 having a half sine wave-like waveform is generated in the turned-off section of the element 26. As a result, a high power factor can be obtained from the power converter and, at the same time, the size of the converter can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a push-pull type power conversion device.

[0002]

2. Description of the Related Art As this type of power conversion device, the one shown in FIG. 5 is known. This is because the input terminal of the full-wave rectifier circuit 2 is connected to the AC power source 1, and the output transformer 4 is connected via the choke coil 3 to the positive electrode side of the output terminal of the full-wave rectifier circuit 2.
Is connected to the middle point t of the primary winding 4p of the
Of the switching elements 5 and 6 on the negative side of the output terminals of
Each end of the primary winding 4p of the output transformer 4 is connected via. A capacitor 7 is connected in parallel to the primary winding 4p of the output transformer 4.

The positive terminal of the output terminal of the full-wave rectifier circuit 2 is connected to the anode of the diode 10 through the first smoothing capacitor 8 and the choke coil 9 in series, and the cathode of the diode 10 is connected to the second smoothing capacitor. It is connected to the negative side of the output terminal of the full-wave rectification circuit 2 via 11. The positive terminal of the output terminal of the full-wave rectifier circuit 2 is connected to the cathode of the diode 12 via the first smoothing capacitor 8, and the anode of the diode 12 is connected to the full-wave rectifier circuit 2.
It is connected to the negative side of the output terminal. Further, the positive side of the output terminal of the full-wave rectification circuit 2 is connected to the cathode of the diode 13, and the anode of the diode 13 is connected to the negative side of the output terminal of the full-wave rectification circuit 2 via the second smoothing capacitor 11. ing.

A capacitor 14 for absorbing high frequency noise is connected between the output terminals of the full wave rectifier circuit 2.

Then, as a load on the secondary winding 4s of the output transformer 4, the filament electrodes 15a, 15 of the fluorescent lamp 15 are loaded.
b is connected.

In this power converter, an AC power source 1
Therefore, when a sinusoidal AC voltage E as shown in (a) of FIG. 6 is applied, a full-wave rectified output is generated at the output terminal of the full-wave rectifier circuit 2.

When the full-wave rectified output is higher than twice the voltage remaining in the smoothing capacitors 8 and 11,
From the positive electrode side of the output terminal of the full-wave rectification circuit 2, the first smoothing capacitor 8, the choke coil 9, the diode 10, and the second
An electric current flows through the smoothing capacitor 11 and the smoothing capacitors 8 and 11 are charged.

Further, the full-wave rectified output is obtained by each smoothing capacitor 8,
When the voltage is equal to or less than twice the voltage remaining in 11 and equal to or higher than the voltage remaining in the smoothing capacitors 8 and 11, the input current flows but the smoothing capacitors 8 and 11 are neither charged nor discharged.

Further, when the full-wave rectified output is less than the voltage remaining in the smoothing capacitors 8 and 11, the input current is stopped and the smoothing capacitors 8 and 11 are discharged. The discharging at this time is performed via the diode 12 for the first smoothing capacitor 8 and via the diode 13 for the second smoothing capacitor 11.

Therefore, the voltage V14 generated across the output terminal of the full-wave rectifier circuit 2, that is, across the capacitor 14, has a maximum voltage equal to the maximum value of the input voltage E, and is a smoothed voltage at half the voltage point. The waveform is as shown in Fig. 6 (b).

The input current IIN from the AC power supply 1 at this time has a waveform shown in FIG. 6 (c).

[0012]

In such a power conversion device, semi-smoothing with a good power factor is possible, but two expensive smoothing capacitors having a relatively large capacity are used,
There is a problem that the device becomes large and expensive.

Therefore, the present invention intends to provide a power conversion device which can obtain a high power factor in the push-pull type and can reduce the size and improve the economical efficiency by using only one smoothing capacitor. Is.

[0014]

According to the present invention, the middle point of the primary winding of an output transformer is connected to the positive electrode side of the output terminal of a full-wave rectification circuit for full-wave rectifying an AC power source, and the full-wave rectification is performed. Connect each terminal of the primary winding of the output transformer to the negative side of the output terminal of the circuit through a switching element respectively, and connect the positive side of the output terminal of the full-wave rectifier circuit and the middle point of the primary winding of the output transformer. A first inductor in series between the switching element and the negative side of the output terminal of the full-wave rectifier circuit and each switching element, and a capacitor is connected in parallel to the primary winding of the output transformer to switch each switching element. In a push-pull type power converter that alternately switches the elements to output an AC voltage to the secondary winding of the output transformer, any one of the push-pull power converters is located at both ends of the primary winding of the output transformer. Winding A series circuit of a first inductor and a second diode having a cathode connected to each other, a second inductance and a smoothing capacitor connected between the positive electrode side of the output terminal of the full-wave rectification circuit and the anode of each diode, and a full-wave A third diode is provided between the output terminals of the rectifier circuit, with a second inductor and a smoothing capacitor connected in series, with the anode being the negative electrode side of the output terminal.

[0015]

In the present invention having such a structure, when the switching elements are alternately turned on and off, a resonance voltage is generated in the parallel circuit of the primary winding of the output transformer and the capacitor. At this time, the voltage at the winding position of the primary winding to which the cathodes of the first and second diodes are connected has a waveform similar to the full-wave rectified waveform, but the resonance voltage and the midpoint of the primary winding From the relationship between the winding position and the winding position and the winding ratio between the winding position and the end of the primary winding, the level changes alternately depending on the ON / OFF operation of each switching element.

At this time, since the diode connected to each winding position selects a lower voltage generated at the winding position to pass the current, a full-wave rectified waveform of a low voltage is effectively applied. Is equivalent to.

The power supply voltage is high, and the charging current to the smoothing capacitor is the second inductance, the smoothing capacitor,
When flowing through any of the first diode or the second diode, the primary winding of the output transformer, or each switching element, the voltage generated at the winding position acts in series with the voltage of the smoothing capacitor. That is, the charging current flows only when the input voltage becomes higher than the sum of the voltage of the smoothing capacitor and the voltage generated at the winding position.
Further, when the input voltage becomes less than the voltage of the smoothing capacitor, the smoothing capacitor will be discharged. Further, when the input voltage is equal to or lower than the sum of the voltage of the smoothing capacitor and the voltage generated at the winding position and is equal to or higher than the voltage of the smoothing capacitor, the smoothing capacitor is neither charged nor discharged.

In this way, one smoothing capacitor can achieve the same effect as the conventional one.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 21 is an AC power source, and an input terminal of a full-wave rectifier circuit 22 is connected to the AC power source 21.

The midpoint t1 of the primary winding 24p of the output transformer 24 is connected to the positive electrode side of the output terminal of the full-wave rectification circuit 22 via the choke coil 23 which is the first inductance, and the full-wave rectification circuit is connected. Each end of the primary winding 24p of the output transformer 24 is connected to the negative side of the output terminal of 22 through switching elements 25 and 26, respectively. A capacitor 27 is connected in parallel to the primary winding 24p of the output transformer 24 to form a push-pull type inverter circuit.

The positive electrode side of the output terminal of the full-wave rectification circuit 22 is connected to the anodes of the first and second diodes 30 and 31 through a choke coil 28 and a smoothing capacitor 29, which are second inductance, in series. There is.

The first diode 30 has its cathode connected to an arbitrary winding position t2 located on one end side connected to the switching element 25 with respect to the midpoint t1 of the primary winding 24p of the output transformer 24. The second diode 31 has its cathode connected to an arbitrary winding position t3 located on the other end side connected to the switching element 26 with respect to the midpoint t1 of the primary winding 24p of the output transformer 24. There is.

The positive terminal of the output terminal of the full-wave rectifier circuit 22 is connected to the choke coil 28 and the smoothing capacitor 29.
Are connected in series to the cathode of the third diode 32. The anode of the third diode 32 is connected to the negative side of the output terminal of the full-wave rectifier circuit 22.

A capacitor 33 for absorbing high frequency noise is connected between the output terminals of the full wave rectifier circuit 22.

The secondary winding 2 of the output transformer 24
Each filament electrode 34 of the fluorescent lamp 34 as a load on 4s
a and 34b are connected.

In the embodiment having such a structure, as shown in FIG.
As shown in (a) and (b) of FIG.
Are alternately turned on and off, a half-wave sinusoidal resonance voltage as shown in (c) of FIG. 2 is generated by the parallel circuit of the primary winding 24p of the output transformer 24 and the capacitor 27 in the off section of the switching element 25. Vs1 is generated, and the parallel circuit of the primary winding 24p of the output transformer 24 and the capacitor 27 in the off section of the switching element 26 causes a change in FIG.
A half-wave sinusoidal resonance voltage Vs2 as shown in (d) is generated.

The resonance voltages Vs1 and Vs2 are alternately generated in this way, but at the winding position t2, the influence of the resonance voltages Vs1 and Vs2 is the number of windings from the midpoint t1 to the winding position t2 and the winding position t2. 2e according to the ratio of the number of windings from
A voltage Vt2 as shown by is generated.

At the winding position t3, the resonance voltages Vs1 and Vs are
The effect of s2 depends on the ratio of the number of windings from the midpoint t1 to the winding position t3 to the number of windings from the winding position t3 to the other end of FIG.
The voltage Vt3 shown in (f) is generated.

At this time, the first and second diodes 30, 3
1 selects the voltage Vt2 or Vt3, whichever is lower, to flow the current, so that the winding positions t2 and t3 in FIG.
This is equivalent to applying the voltage VT shown in (g).

That is, the power supply voltage E is high, and the charging current of the smoothing capacitor 29 is the choke coil 28, the smoothing capacitor 29, the first diode 30, or the second diode 3.
1. When the current flows through the path of the primary winding 24p of the output transformer 24 and the switching element 25 or 26, the voltage VT acts in series with the voltage of the smoothing capacitor 29.

Therefore, the charging current flows in the smoothing capacitor 29 only when the input voltage E becomes higher than the voltage obtained by adding the voltage VT to the voltage of the smoothing capacitor 29.

When the input voltage E becomes less than the voltage of the smoothing capacitor 29, the input current stops and the smoothing capacitor 2
9 discharges and supplies power to the inverter circuit.

Further, when the input voltage E falls below the voltage obtained by adding the voltage VT to the voltage of the smoothing capacitor 29 and above the voltage of the smoothing capacitor 29, the smoothing capacitor 2
9 does not charge or discharge, and the input voltage E is directly applied to the inverter circuit at this time.

Therefore, if the input voltage E from the AC power supply 21 has a sine wave waveform as shown in FIG. 3 (a), the input current IIN at that time becomes as shown in FIG. 3 (b). This input current IIN is a current Im that flows when the power supply voltage as shown in FIG. 3C directly drives the inverter circuit, that is, when the input voltage E is equal to or higher than the voltage of the smoothing capacitor 29.
And the current I D flowing when the input voltage E becomes higher than the voltage obtained by adding the voltage VT to the voltage of the smoothing capacitor 29 as shown in FIG. Becomes

The input current IIN has a zero rest period when the input voltage E becomes less than the voltage of the smoothing capacitor 29.

In this way, the input current phase becomes extremely close to the input voltage phase, so that a high power factor can be obtained. Moreover, only one smoothing capacitor needs to be used, which can reduce the size of the device and improve the economical efficiency.

Next, another embodiment of the present invention will be described with reference to the drawings. The same parts as those in the above embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

As shown in FIG. 4, the choke coil 23, which is the first inductance, is inserted in series between the negative side of the output terminal of the full-wave rectifier circuit 22 and the connection point of the switching elements 25 and 26. .

Even in this case, the operation is the same as that of the above-mentioned embodiment, so that the same effect as that of the above-mentioned embodiment can be obtained.

Since the characteristics of the inverter circuit slightly change when the arrangement of the choke coil 23 is changed in this way, it is necessary to adjust the winding positions t2 and t3.

In each of the above embodiments, the output transformer 2
A description has been given of the case where a fluorescent lamp, which is a load, is directly connected to the secondary winding, but the present invention is not limited to this. For example, a rectifying circuit and a smoothing circuit are connected to the secondary winding to rectify and smooth the secondary side output. Alternatively, the DC output may be provided and the DC output may be supplied to the load.

[0043]

As described above, according to the present invention, in the push-pull type power converter, a high power factor can be obtained, and moreover, it is possible to reduce the size and improve the economical efficiency by using only one smoothing capacitor. it can.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a voltage waveform of each part in the inverter circuit in the embodiment.

FIG. 3 is a diagram showing a voltage waveform and a current waveform of an input section in the embodiment.

FIG. 4 is a circuit configuration diagram showing another embodiment of the present invention.

FIG. 5 is a circuit configuration diagram showing a conventional example.

FIG. 6 is a diagram showing a voltage waveform, a current waveform, and a voltage waveform applied to an inverter circuit of an input section in the conventional example.

[Explanation of symbols]

 21 ... AC power supply 22 ... Full-wave rectification circuit 23 ... Choke coil (first inductance) 24 ... Output transformer 25, 26 ... Switching element 27 ... Capacitor 28 ... Choke coil (second inductance) 29 ... Smoothing capacitor 30, 31 , 32 ... Diode

Claims (1)

[Claims] 1. A midpoint of a primary winding of an output transformer is connected to a positive side of an output terminal of a full-wave rectifier circuit for full-wave rectifying an AC power source, and a negative side of an output terminal of the full-wave rectifier circuit is connected to the positive side. Each end of the primary winding of the output transformer is connected via a switching element, and between the positive side of the output terminal of the full-wave rectifier circuit and the midpoint of the primary winding of the output transformer, or A first inductance is inserted in series between the negative electrode side of the output terminal of the full-wave rectifier circuit and each of the switching elements, and a capacitor is connected in parallel to the primary winding of the output transformer to provide the switching elements. In a push-pull type power conversion device that alternately performs switching operation to output an AC voltage to the secondary winding of the output transformer, the push-pull type power conversion apparatus is located at both ends of the primary winding of the output transformer with respect to the middle point. A first and a second diode having a cathode connected to an arbitrary winding position; and a second inductor and a smoothing capacitor connected between the positive electrode side of the output terminal of the full-wave rectifier circuit and the anode of each diode. And a third diode connected between the output terminal of the series circuit and the output terminal of the full-wave rectification circuit via the series circuit of the second inductance and the smoothing capacitor, with the anode being the negative electrode side of the output terminal. Power conversion device.