JP3231175B2 - Switching power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC power supply, and more particularly to a switching power supply using a commercial AC power supply as an input source.

[0002]

2. Description of the Related Art In recent years, switching power supplies have been frequently used as power supplies for various electronic devices due to their high efficiency conversion characteristics. However, most of them employ a capacitor input method as an input circuit, and thus have a poor power factor. And harmonic components included in the input current have been regarded as a problem. As means for reducing such input harmonic components, for example, FIG.
There is a switching power supply as shown in FIG.

In FIG. 5, 1 is an input AC power supply, 2 is an input filter, 3 is a full-wave rectifier circuit, 4 is a choke coil,
Reference numerals 5 and 6 denote diodes, 7 denotes a smoothing capacitor, 8 denotes switching means, and 9 denotes a reset diode. Reference numeral 10 denotes a transformer having a primary winding 11, a secondary winding 12, and a reset winding 13. 14 and 15 are diodes; 16 is a smoothing choke coil; 17 is an output capacitor;
A rectifying and smoothing circuit is constituted by the smoothing choke coil 16 and the output capacitor 17, and supplies an output DC voltage to the load 18. A control circuit 19 drives the switching means 8 at a predetermined on / off ratio in order to detect and stabilize the output DC voltage.

An AC voltage of an input AC power supply 1 is rectified by a full-wave rectifier circuit 3 via an input filter 2. First, when the switching means 8 is on, a rectified voltage is applied to the choke coil 4, and a choke current flows through the diode 6. At the same time, the voltage of the smoothing capacitor 7 is applied to the primary winding 11 of the transformer 10, a voltage is induced in the secondary winding 12, smoothed by the output capacitor 17 via the diode 14 and the smoothing choke coil 16, and Supplied to

Next, when the switching means 8 is turned off,
The excitation energy stored in the choke coil 4 is emitted via the diode 5 as a choke current for charging the smoothing capacitor 7. At the same time, the excitation energy stored in the transformer 10 is discharged through the reset winding 13 and the reset diode 9 so as to charge the capacitor 7. Further, the excitation energy stored in the smoothing choke coil 16 is released to the output capacitor 17 via the diode 15 and supplied to the load 18.

That is, the choke coil 4, the diodes 5, 6, the switching means 8 and the smoothing capacitor 7 constitute a boost converter which receives the rectified voltage as an input and outputs the rectified voltage to the smoothing capacitor 7, and the smoothing capacitor 7, the switching means 8 and the reset. The diode 9, the transformer 10, the diodes 14, 15, the smoothing choke coil 16, and the output capacitor 17 constitute a feedforward converter using the smoothing capacitor 7 as an input source.

[0007] The output DC voltage is controlled by the control circuit 19 adjusting the on / off period of the switching means 8. On the other hand, assuming that the smoothing capacitor 7 has a sufficiently large capacitance and can be regarded as a voltage source having a DC voltage equivalently, the on / off period is almost constant in a steady state. Since the switching frequency of the switching means 8 is sufficiently higher than the frequency of the input AC voltage, and the change in the rectified voltage can be ignored during one switching cycle, the choke current becomes a triangular wave current having a peak value proportional to the rectified voltage. Since this choke current is smoothed by the input filter to become the input current, the current becomes a sinusoidal current substantially proportional to the input AC voltage, and the input power factor is “1”.
And almost no harmonic components.

[0008]

However, in the above-described conventional configuration, the rectified voltage is input and the smoothing capacitor 7 is used.
Therefore, the voltage of the smoothing capacitor 7 is higher than the input DC voltage (peak value of the rectified voltage) obtained by the normal capacitor input method. In particular, the voltage rise at a light load or at a high input voltage is large, and therefore, the smoothing capacitor 7 and the switching means 8 are required to have high withstand voltage characteristics, and have a problem of design difficulty and efficiency deterioration. .

According to the present invention, even if the output of the boost converter rises due to the addition of a few components, the switching DC / DC
It is an object of the present invention to provide a switching power supply device capable of suppressing an influence on a DC converter and preventing efficiency deterioration.

[0010]

According to the present invention, there is provided a switching power supply device comprising: a boost converter comprising a choke coil, switching means and a diode; a smoothing means for smoothing an output of the boost converter; A switching type DC-DC converter for applying an output voltage of the means as an input voltage source to a primary circuit of a transformer and a series circuit of the switching means to perform DC conversion, wherein the switching means of the step-up converter and the switching DC-DC converter are provided.
In a switching power supply device having a control circuit that also serves as the switching means of the DC converter and drives the switching means so as to stabilize the output voltage of the switching DC-DC converter, the smoothing means includes:
A first and a second capacitor between the first capacitor and the second capacitor;
A first diode is connected in a direction to charge the second capacitor, and a second diode is connected in a direction to discharge the second capacitor between a connection point between the second capacitor and the first diode and the first capacitor. A third diode is connected between a connection point between the first capacitor and the first diode and the second capacitor in a direction of discharging the charge of the first capacitor, and is smoothed. In the means, an input voltage is applied between a connection point between the first capacitor and the second diode and a connection point between the second capacitor and the third diode, and an output voltage is taken out between the connection points. It is characterized by the following.

[0011]

According to this configuration, by using the novel smoothing means, the switching type DC / DC converter can be operated by using a half of the output voltage from the boost converter of the conventional system as an input voltage source. it can.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to FIGS. It is to be noted that components having the same functions as those in FIG.

FIG. 1 shows a first embodiment of the present invention. First
In the switching power supply of the embodiment, a smoothing means 70 is used instead of the smoothing capacitor 7 shown in FIG. The smoothing means 70 includes first and second capacitors 71 and 7.
2 and first to third diodes 73, 74, 75. 1 is an input AC power supply, 2 is an input filter, 3 is a full-wave rectifier circuit, 4 is a choke coil, and 5 and 6 are diodes. 8 is a switching means, 9 is a reset diode, 10 is a transformer, and has a primary winding 11, a secondary winding 12, and a reset winding 13. Reference numerals 14 and 15 denote diodes, reference numeral 16 denotes a smoothing choke coil, and reference numeral 17 denotes an output capacitor. A control circuit 19 drives the switching means 8 at a predetermined on / off ratio in order to detect and stabilize the output DC voltage.

The AC voltage of the input AC power supply 1 is rectified by a full-wave rectifier circuit 3 via an input filter 2. First, when the switching means 8 is on, a rectified voltage is applied to the choke coil 4, and a choke current flows through the diode 6. At the same time, the primary winding 11 of the transformer 10
The voltages of the second capacitors 71 and 72 are applied through third and second diodes 75 and 74, respectively, and a voltage is induced in the secondary winding 12, and the output capacitor is output through the diode 14 and the smoothing choke coil 16. It is smoothed at 17 and supplied to the load 18.

Next, when the switching means 8 is turned off,
The excitation energy stored in the choke coil 4 is emitted as a choke current that charges the first and second capacitors 71 and 72 in series via the diode 5 and the first diode 73. At the same time, the excitation energy stored in the transformer 10 is discharged through the reset winding 13 and the reset diode 9 to charge the second capacitor 72. Further, the excitation energy stored in the smoothing choke coil 16 is released to the output capacitor 17 via the diode 15 and supplied to the load 18.

That is, the choke coil 4, the diodes 5, 6, the switching means 8 and the smoothing means 70 receive a rectified voltage as input, and the first capacitor 71, the first diode 73 and the second A boost converter for outputting to the series circuit of the capacitor 72 is configured.

Smoothing means 70, switching means 8, reset diode 9, transformer 10, diodes 14, 1
5. The smoothing choke coil 16 and the output capacitor 17
A feedforward converter having a parallel circuit formed by the first and second capacitors 71 and 72 via the second and third diodes 74 and 75 as an input source is configured. The voltage of the output capacitor 17 (output DC voltage) is
The switching function can be stabilized by the control function of the on / off ratio of the switching means 8.

Here, the first and second capacitors 71, 7
2 has a sufficiently large capacitance, and assuming that each of them can be regarded as a voltage source having a DC voltage Ec equivalently, the on / off period is almost constant in a steady state. The switching frequency of the switching means 8 is sufficiently higher than the frequency of the input AC voltage, and a change in the rectified voltage can be ignored during one switching cycle. The choke current is a triangular wave current having a peak value substantially proportional to the rectified voltage.
Since this choke current is smoothed by the input filter to become the input current, the current becomes a sine-wave current substantially proportional to the input AC voltage, and the input power factor is close to 1 and almost no harmonic components are obtained. If the smoothing means 70 is simply the smoothing capacitor 7 as in the conventional example, the voltage thereof corresponds to 2Ec in the present embodiment, and the switching type DC / DC
If the converter is also designed to have an input voltage of 2Ec and the clamp voltage of the flyback voltage by the reset winding is also 2Ec, the withstand voltage of the switching means 8 is at least 4Ec.
In the present embodiment, what is necessary is that the clamp voltage of the flyback voltage by the reset winding becomes Ec, so that the withstand voltage of the switching means 8 can be 3 Ec.

That is, the maximum amplitude of the input AC voltage is Ei
In this case, if 2Ec <(4 · Ei / 3), normal switching means at the time of capacitor input can be used.

As described above, according to the present embodiment, the AC voltage from the input AC power supply 1 is input through the full-wave rectifier circuit 3 and the step-up type comprising the choke coil 4, the switching means 8, and the diodes 5, 6. A converter is configured, and a smoothing means 70 is connected to the output of the boost converter. The smoothing means 70 is connected in series via a first diode 73 in a direction in which the first and second capacitors 71 and 72 are charged, and has a positive terminal of the first capacitor 71 and a positive terminal of the second capacitor 72. A second diode 74 is connected between the negative terminal of the first capacitor 71 and the negative terminal of the second capacitor 72, and a second diode 74 is connected between the negative terminal of the first capacitor 71 and the negative terminal of the second capacitor 72. The third diode 75 is connected in the direction in which the capacitor 71 is discharged. A transformer 10 having a primary winding 11, a secondary winding 12, and a reset winding 13; a reset diode 9; a secondary diode 9; By configuring a switching type DC-DC converter having rectifying and smoothing circuits including diodes 14 and 15 connected to the windings, a smoothing choke coil 16 and an output capacitor 17, switching which is too high in the conventional method is achieved. Formula DC-DC
The input voltage of the converter can be halved and the withstand voltage of the switching means 8 can be reduced to "3/4".

Although the first embodiment shown in FIG. 1 is an application of the present invention to the conventional example shown in FIG. 5, there are other power factor improving type switching power supplies of this kind. Needless to say, the present invention can be applied.

FIGS. 2 to 4 show second, third and fourth embodiments, respectively, in which a smoothing means 70 is used.
The components having the same functions as those of the first embodiment shown in FIG. 1 are denoted by the same reference numerals. In any case, when only the smoothing capacitor 7 is used without applying the smoothing means 70 according to the present invention, the voltage is high and it becomes difficult to design a switching type DC / DC converter.
By applying 0, the input voltage of the switching DC-DC converter, which has become too high, can be halved.

More specifically, the second embodiment shown in FIG.
The present invention is further applied to a flyback converter provided with a power factor improving means as shown in FIG. Since the switching type DC-DC converter is a flyback converter, the reset winding 13 and the reset diode 9 shown in FIG. 2 or FIG. It comprises a diode 14 for rectifying the voltage and an output capacitor 17 for smoothing. Primary winding 11 and secondary winding 12 of transformer 10
If the turns ratio and "n", the output voltage is "E _0", the breakdown voltage of the switching means 8 is "2 · E ₀ +
It is easy to see that n · E ₀ ″.

In the third embodiment shown in FIG. 3, the present invention is applied to a continuous choke current type power factor correction converter in which the diode 6 in FIG. In the fourth embodiment shown in FIG. 4, choke coils 41 and 42 and diodes 51, 52, 61 and 62 are used instead of choke coil 4 and diodes 5 and 6 in FIG. 5, and flow through the choke coil. The number of diodes interposed in the current path is reduced, and the present invention is applied to the power factor improving converter previously applied by the inventors. The choke coil 41 and the choke coil 42 are wound around a common core and electromagnetically coupled. 31 and 32 are diodes.

[0025]

As described above, according to the present invention, a boost converter composed of a choke coil, switching means and a diode, a smoothing means for smoothing the output of the boost converter, A switching type DC-D for applying an output voltage as an input voltage source to a series circuit of a primary winding of a transformer and switching means to perform DC conversion.
A switching type DC-D converter, wherein the switching means of the step-up converter and the switching means of the switching type DC-DC converter are provided.
In a switching power supply having a control circuit for driving said switching means to stabilize an output voltage of a C converter, said smoothing means is provided between a first capacitor and a second capacitor. A first diode is connected in the direction of charging the second capacitor, and a second diode is connected between the connection point of the second capacitor and the first diode and the first capacitor in a direction of discharging the second capacitor. And a third diode connected between the connection point between the first capacitor and the first diode and the second capacitor in a direction of discharging the electric charge of the first capacitor. Applies an input voltage between a connection point between the first capacitor and the second diode and a connection point between the second capacitor and the third diode, and obtains an output voltage from between the connection points. An excellent device that can operate a switching type DC / DC converter by using the voltage of half of the output voltage from the conventional boost type converter as an input voltage source by using the smoothing means. Can be realized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a first embodiment of a switching power supply device of the present invention.

FIG. 2 is a configuration diagram of a second embodiment.

FIG. 3 is a configuration diagram of a third embodiment.

FIG. 4 is a configuration diagram of a fourth embodiment.

FIG. 5 is a configuration diagram of a conventional switching power supply device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Input AC power supply 3 Full-wave rectification smoothing circuit 4 Choke coil 5 Diode 6 Diode 70 Smoothing means 71 First capacitor 72 Second capacitor 73 First diode 74 Second diode 75 Third diode 8 Switching means 9 Reset Diode 10 Transformer 14,15 Diode 16 Smooth choke coil 17 Output capacitor

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Yoshinori Kobayashi 10-13 Minamicho, Hanno City, Saitama Prefecture Inside Shindengen Industry Co., Ltd. (72) Inventor Yutaka Sekine 10-13 Minamimachi, Hanno City, Saitama Prefecture Shindengen (56) References JP-A-5-328724 (JP, A) JP-A-5-276756 (JP, A) JP-A-4-364371 (JP, A) (58) Fields surveyed ( Int.Cl. ⁷ , DB name) H02M 7/06 H02M 3/28

Claims (1)

(57) [Claims] 1. A boost converter comprising a choke coil, a switching means and a diode, a smoothing means for smoothing an output of the boost converter, and a primary of a transformer using an output voltage of the smoothing means as an input voltage source. A switching type DC-DC converter for applying a direct current to a series circuit of a winding and a switching means for DC conversion;
The switching means of the C-DC converter,
In a switching power supply device having a control circuit for driving the switching means so as to stabilize an output voltage of a switching DC-DC converter, the smoothing means is provided between a first capacitor and a second capacitor.
A first diode is connected in a direction for charging the second capacitor, and a second diode is connected in a direction for discharging the second capacitor between a connection point between the second capacitor and the first diode and the first capacitor. And a third diode connected between a connection point between the first capacitor and the first diode and the second capacitor in a direction to discharge the electric charge of the first capacitor. An input voltage is applied to the smoothing means between a connection point between the first capacitor and the second diode and a connection point between the second capacitor and the third diode; Take out the switching power supply.