JPH07303375A - Method for improving power factor of switching power unit and switching power unit - Google Patents

Abstract

PURPOSE:To improve the power factor of a switching power unit so as to suppress the generation of harmonic components by discharging both a smoothing capacitor and charging-discharging capacitor when the voltage between the terminals of the charging-discharging capacitor drops to a prescribed value. CONSTITUTION:A switching power unit is constituted by connecting one end of a charging-discharging capacitor 17 to the output terminal 3 of a full-wave rectifier 2 and the other end of the capacitor 17 to the other end of a smoothing capacitor 5, and then, connecting a third diode between one end of the capacitor 17 and a dividing point at which a primary winding 15 is divided at a prescribed turns ratio. Although a sine-wave AC voltage Vs is full-wave rectified by means of the rectifier 2 when AC power supply 1 is made, the output current I of the rectifier 2 is changed by shifting the charging timing, because the voltage v5 across the terminals of the capacitor 5 is relatively high and the voltage v17 across the terminals of the capacitor 17 is relatively low. As a result, the power factor of the power unit 100 is improved and the generation of harmonic components is suppressed, because the waveform of the electric current of the AC power supply 1 is relieved in steepness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power factor correction method for a switching power supply and a switching power supply,
More particularly, the present invention relates to a power factor improving method for a switching power source device capable of improving the power factor of a circuit as compared with a conventional one, and a switching power source device implementing the power factor improving method.

[0002]

2. Description of the Related Art FIG. 4 is an overall configuration diagram showing an example of a conventional switching power supply device. The switching power supply device 500 has a circuit configuration generally called a capacitor input type rectifying / smoothing circuit. That is, the sine wave AC voltage Vs from the AC power supply 1 is full-wave rectified by the full-wave rectifier 2, and the full-wave rectified voltage between the pair of output terminals 3 and 4 is smoothed by the smoothing capacitor 55. The voltage v55 is input to the input terminals 7 and 8 of the DC-DC converter 6, and a stable output voltage Vo is supplied to the load 11 from the output terminals 9 and 10 of the DC-DC converter 6.

Next, the switching power supply device 500 described above.
The operation of will be described. As shown in FIG. 5A, the AC power supply 1 outputs a sine wave AC voltage Vs. If a numerical example is shown, the effective value of the sine wave AC voltage Vs is 100V.
Then, the peak value Vm is about 140V. Time to
When the power switch K is closed and the AC power supply 1 is turned on, the sine wave AC voltage Vs is full-wave rectified by the full-wave rectifier 2 to obtain a full-wave rectified voltage as shown in FIG. To be

As shown in FIG. 5 (b), times to-t
During the period of o ′, the full-wave rectified voltage rises, so that the charging current i is applied to the smoothing capacitor 55 as shown in FIG.
55 flows. At this time, as shown in FIG.
The inter-terminal voltage v55 of the smoothing capacitor 55 is the peak value Vm.
Rise to. As shown in FIG. 5B, time to '
After that, the full-wave rectified voltage drops, so that the smoothing capacitor 55 is discharged to the DC-DC converter 6 side. Therefore, as shown in FIG. 5D, the inter-terminal voltage v55 gradually decreases.

When the full-wave rectified voltage rises again and the full-wave rectified voltage becomes equal to the inter-terminal voltage v55 at time t1, FIG.
As shown in (c) of FIG.
55 flows and the smoothing capacitor 55 is charged. Therefore, as shown in FIG. 5D, the inter-terminal voltage v55 rises and reaches the peak value Vm at the time t2. After time t2, the operations after to 'are repeated.

[0006]

In the above conventional switching power supply device 500, as shown in FIG.
The charging current i55 has a steep pulse waveform. Therefore, there is a problem that the current waveform from the AC power source 1 also has a steep pulse shape, the power factor is lowered, and a large amount of harmonic components are generated. Therefore, it is an object of the present invention to provide a power factor improving method for a switching power source device capable of improving the power factor and suppressing the generation of harmonic components, and a switching power source device implementing the power factor improving method. .

[0007]

According to a first aspect of the present invention, the present invention smoothes a rectified voltage obtained by a rectifying circuit for rectifying an AC voltage with a smoothing capacitor, and generates a voltage based on a voltage between terminals of the smoothing capacitor. In a switching power supply device which is intermittently applied to both ends of a primary winding of a transformer and supplies a voltage induced in a secondary winding of the transformer to a load side, the charging is performed by a rectified voltage obtained by the rectifier circuit. A charging / discharging capacitor that discharges the primary winding to a dividing point that divides the primary winding at a predetermined winding ratio is provided, and the charging / discharging capacitor is charged when the rectified voltage becomes higher than the terminal voltage of the charging / discharging capacitor. The smoothing capacitor is charged when the rectified voltage becomes higher than the inter-terminal voltage of the smoothing capacitor, and the smoothing capacitor is charged when the rectified voltage starts to decrease. Is discharged from the charging / discharging capacitor without discharging from the charging / discharging capacitor, and when the voltage between terminals of the charging / discharging capacitor drops to a predetermined voltage, discharging is performed from both the smoothing capacitor and the charging / discharging capacitor. Provided is a method for improving the power factor of a switching power supply device.

In a second aspect, the present invention smoothes a rectified voltage obtained by a rectifying circuit for rectifying an AC voltage with a smoothing capacitor, and intermittently applies a voltage based on a voltage between terminals of the smoothing capacitor to the transformer 1. In a switching power supply device that applies a voltage applied to both ends of a secondary winding and induces a voltage induced in a secondary winding of the transformer to a load side, a switching power supply device is provided between one output side of the rectifier circuit and one end of the smoothing capacitor. One diode is connected, a second diode is connected between one end of the smoothing capacitor and one end of the primary winding in the same direction as the first diode, and one output side of the rectifier circuit is charged and discharged. One end of the capacitor is connected, the other end of the charging / discharging capacitor is connected to the other end of the smoothing capacitor, and one end of the charging / discharging capacitor and the primary winding are divided at a predetermined turn ratio. That to provide a switching power supply device according to claim a third diode between the dividing points that formed by connecting in the same direction as the first diode.

According to a third aspect of the present invention, in the switching power supply device having the above structure, one end of a fourth diode in the same direction as the first diode is connected to one output side of the rectifying circuit, and the fourth diode of the fourth diode is connected. One end of the auxiliary charging / discharging capacitor is connected to the other end, one end of a fifth diode in the same direction as the first diode is connected to one end of the auxiliary charging / discharging capacitor, and the other end of the fifth diode is connected to one end. A switching power supply device characterized in that it is connected to an auxiliary split point provided between one end of the next winding and the split point, and the other end of the auxiliary charging / discharging capacitor is connected to the other end of a smoothing capacitor. provide.

[0010]

In the power factor improving method according to the first aspect and the switching power supply apparatus according to the second aspect, the above-mentioned 1 is provided in addition to the smoothing capacitor discharged to the primary winding of the transformer.
A charging / discharging capacitor that discharges was provided at the dividing point of the next winding. Since the voltage at the dividing point is lower than the voltage at the primary winding of the transformer, the voltage across the smoothing capacitor is relatively high, and the voltage across the charging / discharging capacitor is relatively low. Due to this voltage difference, the charging timing of the smoothing capacitor and the charging timing of the charging / discharging capacitor are deviated in time. Then, the current waveform from the AC power supply, which is the sum of the charging current of the smoothing capacitor and the charging current of the charging / discharging capacitor, is steeper than the pulse-shaped waveforms of the charging current of the smoothing capacitor and the charging current of the charging / discharging capacitor. Is a relaxed waveform. Therefore, the power factor is improved and the generation of harmonic components is suppressed.

In the switching power supply device according to the third aspect, in addition to the smoothing capacitor discharging to the primary winding of the transformer and the charging / discharging capacitor discharging to the dividing point of the primary winding, the primary winding is also provided. An auxiliary charging / discharging capacitor that discharges is provided at the auxiliary dividing point. Since the voltage between the terminals of the smoothing capacitor, the voltage between the terminals of the charging / discharging capacitor, and the voltage between the terminals of the auxiliary charging / discharging capacitor are different, the charging timing is shifted in time. Therefore, the steepness of the current waveform from the AC power source is further alleviated, the power factor is improved, and the generation of harmonic components is suppressed. In addition,
You may provide one or more auxiliary division points.

[0012]

The present invention will be described in more detail with reference to the embodiments shown in the drawings. The present invention is not limited to this.

FIG. 1 is an overall configuration diagram showing a switching power supply device according to a first embodiment of the present invention. This switching power supply device 100 has a circuit configuration generally called a forward converter. That is, the power switch K
Is closed, the sine wave AC voltage Vs generated by the AC power source 1
Is full-wave rectified by the full-wave rectifier 2, and the full-wave rectified voltage between the pair of output terminals 3 and 4 is smoothed by the smoothing capacitor 5. The switch 16 connected in series with the primary winding 15 of the transformer 14 is turned on / off by the PWM control unit 24, so that the inter-terminal voltage v5 of the smoothing capacitor 5 is applied to both ends of the primary winding 15. Apply intermittently. Then, the voltage induced in the secondary winding 19 of the transformer 14 is converted into a direct current by the rectifying diode 20, the free wheeling diode 21, the choke coil 22, and the capacitor 23 to output the output voltage Vo.
Is supplied to the load 11. The output voltage Vo is supplied to the PW via the error detector 26 and the photocoupler 25.
It is fed back to the M control unit 24 and used for stabilization control.

In addition to the above configuration, in the switching power supply device 100, the first diode 12 is connected between the output terminal 3 of the full-wave rectifier 2 and one end of the smoothing capacitor 5, and one end of the smoothing capacitor 5 is connected. The second diode 13 is connected between the first winding 15 and one end of the primary winding 15. Further, one end of the charging / discharging capacitor 17 is connected to the output terminal 3 of the full-wave rectifier 2, and the other end of the charging / discharging capacitor 17 is connected to the other end of the smoothing capacitor 5. A third diode 18 is connected in the same direction as the first diode 12 between one end of the charging / discharging capacitor 17 and a dividing point 27 that divides the primary winding 15 at a predetermined turn ratio. . The winding between one end (upper end in the figure) of the primary winding 15 and the dividing point 27 is 15a (number of turns n1), and the other end (lower end in the figure) of the primary winding 15 and The winding between the division point 27 and 15b (number of turns n2).

Next, the operation of the switching power supply device 100 will be described. For convenience of explanation, it is assumed that the following conditions are satisfied. The frequency at which the switch 16 is turned on / off is sufficiently higher than the frequency of the sine wave AC voltage Vs. The diodes 12, 13, 18 are ideal diodes. The winding number ratio of the primary winding 15 is set to n1: n2 = 1: 1.

As shown in FIG. 2A, the AC power supply 1 outputs a sinusoidal AC voltage Vs. As a numerical example, assuming that the effective value of the sine wave AC voltage Vs is 100V, the peak value Vm is about 140V. When the power switch K is closed and the AC power supply 1 is turned on at the time to, the sine wave AC voltage Vs is full-wave rectified by the full-wave rectifier 2 to generate
As shown in (b) of the above, a full-wave rectified voltage is obtained.

As shown in (c) of FIG.
During the period of o ′, the full-wave rectified voltage rises, so that the charging current i5 is applied to the smoothing capacitor 5 as shown in FIG.
Flows. At this time, as shown in FIG. 2D, the inter-terminal voltage v5 of the smoothing capacitor 5 rises to the peak value Vm. Further, as shown in (e) of FIG. 2, the charging current i17 flows through the charging / discharging capacitor 17. At this time, as shown in (f) of FIG.
The inter-terminal voltage v17 of No. 7 rises to the peak value Vm.

After the time to ', the full-wave rectified voltage decreases as shown in FIG. 2 (b). Therefore, the charging / discharging capacitor 17 discharges and current flows through the winding 15b,
As shown in FIG. 2F, the inter-terminal voltage v17 gradually decreases. On the other hand, (v17 / n2)> (v5-v17)
/ N1, the second diode 13 is in the reverse bias state, and the inter-terminal voltage v17 <the inter-terminal voltage v5. Therefore, the first diode 12 is also in the reverse bias state, so that the smoothing capacitor 5 is not charged. It is not discharged, and the terminal voltage v5 is kept at the peak value Vm.

The voltage v17 between terminals further decreases, and at time t
When (v17 / n2) = (v5-v17) / n1 in a, the second diode 13 becomes conductive and the smoothing capacitor 5 also starts discharging. Therefore, after the time ta, FIG.
As shown in (d), the inter-terminal voltage v5 also gradually decreases. At this time, the third diode 18 blocks the energy of the smoothing capacitor 5 from flowing into the charging / discharging capacitor 17. In the above numerical example, the inter-terminal voltage v17 (= Vn) at time ta is about 70V.

At the time t3, the full-wave rectified voltage rises again.
Then, when the full-wave rectified voltage becomes equal to the inter-terminal voltage v17,
As shown in FIG. 2E, the charging current i17 flows by the full-wave rectified voltage, and the charging / discharging capacitor 17 is charged. Then, as shown in (f) of FIG.
17 rises. Then, v17 / n2> (v5-v1
7) / n1, the second diode 13 is in a reverse bias state, and the terminal voltage v17 <the terminal voltage v
Therefore, the smoothing capacitor 5 is neither charged nor discharged because the first diode 12 is also in the reverse bias state.
The terminal voltage v5 is maintained at the voltage Vt. In the above numerical example, the terminal voltage v5 (= Vt) at time t3 is about 100.
V. Further, the voltage v17 (= V between terminals at time t3
u) is about 50V.

At the time t4, the full-wave rectified voltage further rises.
Then, when the full-wave rectified voltage becomes equal to the inter-terminal voltage v5 (= Vt), as shown in FIG.
Also, the charging current i5 flows, and the smoothing capacitor 5 is charged. Then, as shown in (d) of FIG.
5 rises. After time t5, the operations after to 'are repeated.

After all, the output current I from the full-wave rectifier 2 changes as shown in (g) of FIG. this is,
The steepness of the waveform is relaxed as compared with the output current (that is, the charging current i55) from the full-wave rectifier 2 in the conventional switching power supply device 500 described above with reference to FIG. Therefore, the current from the AC power supply 1 has a waveform with a steepness alleviated, and the power factor is improved (when the conventional power factor is about 0.6, it can be improved to about 0.7),
The generation of harmonic components will be suppressed. Further, this makes it possible to comply with the harmonic current regulations [regulation content is based on the international standard IEC1000-3-2 by IEC (International Electrotechnical Commission)] scheduled to start in 1996.

-Second Embodiment- FIG. 3 is an overall configuration diagram showing a switching power supply device according to a second embodiment of the present invention. This switching power supply 2
00 is different from the switching power supply device 100 of the first embodiment in the following points. That is, one end of the fourth diode 31 is connected to the output terminal 3 of the full-wave rectifier 2, one end of the auxiliary charging / discharging capacitor 37 is connected to the other end of the fourth diode 31, and the auxiliary charging / discharging capacitor 37 One end of the fifth diode 32 is connected to one end, and the other end of the fifth diode 32 is connected to an auxiliary split point 33 provided between one end of the primary winding 15 of the transformer 14 and the split point 27 '. .
The other end of the auxiliary charging / discharging capacitor 37 is connected to one end of the smoothing capacitor 5 (that is, the output terminal 4 of the full-wave rectifier 2).

In the diode 31, the energy of the auxiliary charging / discharging capacitor 37 is the charging / discharging capacitor 17
Prevent it from flowing into. In addition, the diode 32
Prevents the energy of the smoothing capacitor 5 from flowing into the auxiliary charging / discharging capacitor 37.

Switching power supply unit 2 of the second embodiment
According to 00, in addition to applying the inter-terminal voltage of the charging / discharging capacitor 17 to the dividing point 27 ′ of the primary winding 15, the inter-terminal voltage of the auxiliary charging / discharging capacitor 37 is applied to the primary winding 15 Since it is configured to be applied to the auxiliary division point 33 of
The charging timing of the smoothing capacitor 5, charging of the charging / discharging capacitor 17 and charging timing of the auxiliary charging / discharging capacitor 37 become different, and the steepness of the output current waveform from the full-wave rectifier 2 is further alleviated. Therefore, AC power supply 1
Current has a waveform with reduced steepness, the power factor is improved, and the generation of harmonic components is suppressed.

In the second embodiment, the transformer 14 is used.
Although one auxiliary division point 33 is provided between one end of the primary winding 15 and the division point 27 ', a plurality of auxiliary division points may be provided. Further, in the first and second embodiments, the circuit configuration of the switching power supply device is the forward converter, but it may be a flyback converter. further,
The switching power supply device may be a self-excited system,
The separately excited method may be used.

[0027]

According to the power factor improving method for a switching power supply of the present invention, the power factor can be improved and the generation of harmonic components can be suppressed. Further, according to the switching power supply device of the present invention, the power factor can be improved at low cost without using expensive parts such as a power factor improving IC. Further, since energy is stored in both the smoothing capacitor and the charging / discharging capacitor, the ability to maintain the output voltage with respect to a momentary power failure of the AC voltage is increased.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing a switching power supply device according to a first embodiment of the present invention.

FIG. 2 is a waveform diagram for explaining the operation of the switching power supply device of FIG.

FIG. 3 is an overall configuration diagram showing a switching power supply device according to a second embodiment of the present invention.

FIG. 4 is an overall configuration diagram showing an example of a conventional switching power supply device.

5 is a waveform diagram for explaining the operation of the switching power supply device of FIG.

[Explanation of symbols]

 100,200 Switching power supply device 1 AC power supply 2 Full wave rectifier 3,4 Output terminal 5 Smoothing capacitor 11 Load 12, 13, 18 Diode 14 Transformer 15 Primary winding 15a, 15b Winding 16 Switch 17 Charge / discharge capacitor 19 2 Next winding 20 Rectifying diode 21 Freewheeling diode 23 Choke coil 24 PWM control unit 25 Photocoupler 26 Error detection unit 27,27 'Dividing point 31,32 Diode 33 Auxiliary dividing point 37 Auxiliary charging / discharging capacitor K Power switch

Claims (3)

[Claims] 1. A rectified voltage obtained by a rectifying circuit for rectifying an AC voltage is smoothed by a smoothing capacitor, and a voltage based on a voltage between terminals of the smoothing capacitor is intermittently applied to both ends of a primary winding of a transformer. In a switching power supply device that supplies a voltage induced in a secondary winding of the transformer to a load side, the primary winding is divided by a predetermined turn ratio while being charged by the rectified voltage obtained by the rectifying circuit. A charging / discharging capacitor that discharges to a dividing point is provided, and the charging / discharging capacitor is charged when the rectified voltage becomes higher than the terminal voltage of the charging / discharging capacitor, and the rectification voltage is higher than the terminal voltage of the smoothing capacitor. Becomes higher, the smoothing capacitor is charged, and when the rectified voltage starts decreasing, the smoothing capacitor is not discharged and the charging / discharging capacitor is charged. Discharged from capacitor, power factor correction method of the switching power supply voltage between the terminals of the charging and discharging capacitor is characterized in that the discharge from both of the smoothing capacitor and the charging and discharging capacitor and decreases to a predetermined voltage. 2. A rectified voltage obtained by a rectifying circuit for rectifying an AC voltage is smoothed by a smoothing capacitor, and a voltage based on a voltage between terminals of the smoothing capacitor is intermittently applied to both ends of a primary winding of a transformer. In a switching power supply device that supplies a voltage induced in a secondary winding of the transformer to a load side, a first diode is connected between one output side of the rectifier circuit and one end of the smoothing capacitor, A second diode is connected between one end of the capacitor and one end of the primary winding in the same direction as the first diode, and one end of a charging / discharging capacitor is connected to one output side of the rectifier circuit, The other end of the charging / discharging capacitor is connected to the other end of the smoothing capacitor, and a third die is provided between one end of the charging / discharging capacitor and a dividing point at which the primary winding is divided at a predetermined turn ratio. Switching power supply apparatus characterized by formed by connecting over de in the same direction as the first diode. 3. The switching power supply device according to claim 2, wherein one end of a fourth diode in the same direction as the first diode is connected to one output side of the rectifier circuit, and the other end of the fourth diode is supplemented. One end of a discharging capacitor is connected, one end of a fifth diode in the same direction as the first diode is connected to one end of the auxiliary charging / discharging capacitor, and the other end of the fifth diode is connected to one end of a primary winding. And an auxiliary dividing point provided between the dividing points, and the other end of the auxiliary charging / discharging capacitor is connected to the other end of the smoothing capacitor.