JP2000232781A - Switching power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an efficient and low-noise switching power supply device that prevents unwanted resonance current and voltage caused by switching over a wide load range. SOLUTION: Inductors 41a and 41b which are connected each other are connected to both the terminals of the primary coil winding of a transformer, two sets of switching means 21/22 and 23/24 are connected to the other end of each of the inductors 41a and 41b, one end of each of diodes 51 and 52 is connected to both the terminals of the primary coil winding of the transformer, the other of each of the diodes 51 and 52 is connected to a power supply. Then, the two switching means 21/22 and 23/24 for composing a series connection body have a short pause period and are turned on and off alternately. The voltage phase difference of the connection point of two sets of the series connection bodies is set to 180 deg.C, and the on/off ratio of switching elements 21a, 22a, 23a, and 24a included in each switching means is controlled for adjusting the output voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply for supplying a stabilized DC voltage to industrial or consumer electronic equipment.

[0002]

2. Description of the Related Art In recent years, switching power supplies have been strongly required to be smaller, have higher output stability, and have higher efficiency, as electronic equipment has become more inexpensive, smaller, more efficient, and more energy efficient. Hereinafter, a full-bridge converter as an example of a conventional switching power supply that meets the above demand will be described with reference to FIG. FIG. 6 is a circuit diagram showing a configuration of a conventional full-bridge converter. FIG.
, The input DC power supply 111 is connected to the input terminals 112a, 1
12b. First switching element 1
21a and the second switching element 122a are connected in series between the input terminals 112a and 112b,
1 are alternately turned on at a duty ratio of 50% or less according to the control signal output from the controller. Third switching element 123
a and the fourth switching element 124a are connected to the input terminal 1
It is connected in series between 12a and 112b. The third switching element 123a is the second switching element 1
Control is performed such that on / off is repeated at the same timing as 22a. The fourth switching element 124a is controlled so as to be repeatedly turned on and off at the same timing as the first switching element 121a.

A first switching element 121a and a second switching element 121a
Of the switching element 122a, the third switching element 123a, and the fourth switching element 124a,
Parasitic capacitors exist in parallel. In FIG.
Capacitors 121c and 12c
2c, 123c, and 124c. The transformer 131 includes a primary winding 131a and a first secondary winding 131b.
And a second secondary winding 131c. Primary winding 13
1a, the first secondary winding 131b, and the second secondary winding 131
The turn ratio with c is n: 1: 1. Transformer 13
The first terminal of the first primary winding 131a is connected to a connection point between the first switching element 121a and the second switching element 122a. Primary winding 1 of transformer 131
The second terminal of the third switching element 123a
And the fourth switching element 124a.

The operation of the conventional full-bridge converter will be described below with reference to FIG. FIG. 7 is an operation waveform diagram of a conventional full-bridge converter. In FIG. 7, G1, G2, G3 and G4 are the first
To the fourth switching elements 121a, 122a, 12
The control signals of 3a and 124a are shown, respectively. 7, V122 is a second switching element 122.
V124a indicates a voltage applied to the fourth switching element 124a, and V131a indicates a primary winding 131a of the transformer 131.
Shows the voltage applied to. In FIG. 7, I13
Reference numeral 1a denotes a current flowing through the primary winding 131a of the transformer 131, and I121 denotes a first switching element 12a.
1a and a current flowing in a parallel circuit of the capacitor 121c, and the waveform of I122 indicates the second switching element 1
The current flowing in the parallel circuit of the capacitor 22a and the capacitor 122c is shown. In FIG. 7, times T0 to T4 are shown in order to show a temporal change of the operation state.

At time T0, the first switching element 121 is controlled by the control signals G1 and G4 of the control circuit 171.
a and the fourth switching element 124a are simultaneously turned on, the voltage V13 of the primary winding 131a of the transformer 131 is
1a becomes the input voltage [Vin]. The voltage V131b of the first secondary winding 131b of the transformer 131 and the voltage V131c of the second secondary winding 131c are each a voltage [Vi
n / n]. Therefore, the diode 161 is turned on,
The diode 162 turns off, and the third inductor 16
3 becomes the voltage [Vin / n-Vout]. In addition, a current that is the sum of the exciting current of the primary winding 131a of the transformer 131 and the primary-side converted current of the current flowing through the third inductor 163 flows through the first switching element 121a. The primary-side converted current is the third inductor 1
63 is obtained by converting the current flowing through 63 into a current flowing through the primary winding 131a. However, at time T0,
The first switching element 121a receives the voltage [Vin / 2]
At the moment when the voltage is applied, the capacitor 121c is discharged from the off state (non-conducting state) and turned on (conducting state), and the discharging of the capacitor 121c and the charging of the capacitor 122c are instantaneous. Therefore, a spike current flows as indicated by I121 in FIG. Hereinafter, transition from off (non-conductive state) to on (conductive state) is referred to as turn-on. The transition from on to off is referred to as turn-off.

At time T1, when the first switching element 121a and the fourth switching element 124a are simultaneously turned off, the secondary current of the transformer 131 is changed to the first current so that the excitation energy of the third inductor 163 becomes continuous. Secondary winding 131b and second secondary winding 131c
Flows divided into. At this time, both the diode 161 and the diode 162 are on, and the first secondary winding 13
1b and the voltages V131b, V131 of the second secondary winding 131c.
131c becomes zero. At this time, the voltage V163 of the third inductor 163 becomes the voltage [−Vout]. Further, at the moment when the first switching element 121a and the fourth switching element 124a are turned off, unnecessary energy as shown by V131a in FIG. 7 is generated due to the energy stored in the leakage inductance of the transformer and the parasitic inductance of the wiring. A resonance voltage occurs.

At time T2, when the second switching element 122a and the third switching element 123a are simultaneously turned on, the primary winding 131a of the transformer 131 is turned on.
Becomes the voltage [−Vin]. As a result, the first secondary winding 131b of the transformer 131 and the second
, The voltages V131b and V131c of the secondary winding 131c become the voltage [−Vin / n]. As a result, the diode 1
61 turns off, diode 162 turns on,
The voltage V163 of the third inductor 163 is equal to the voltage [Vin
/ N-Vout]. At this time, the second switching element 122a and the third switching element 123a receive a sum of the exciting current of the primary winding 131a of the transformer 131 and the primary-side converted current of the current flowing through the third inductor 163. Flows. The primary-side converted current is obtained by converting a current flowing through the third inductor 163 into a current flowing through the primary winding 131a. Also, at time T2, at the moment when the second switching element 122a and the third switching element 123a are simultaneously turned on, spike noise occurs as in time T0.

At time T3, when the second switching element 122a and the third switching element 123a are simultaneously turned off, the secondary current of the transformer 131 is changed to the first current so that the excitation energy of the third inductor 163 becomes continuous. The current flows while being divided into a secondary winding 131b and a second secondary winding 131c. As a result, both the diode 161 and the diode 162 are turned on, and the first secondary winding 131 is turned on.
b and the voltages V131b, V1 of the second secondary winding 131c.
31c are both zero. At this time, the voltage V163 of the third inductor 163 becomes the voltage [-Vout]. At time T3, the second switching element 122
At the moment when a and the third switching element 123a are simultaneously turned off, an unnecessary resonance voltage is generated as in the case of the time T1.

At time T4, when first switching element 121a and fourth switching element 124a are simultaneously turned on, primary winding 131a of transformer 131 is turned on.
Becomes the input voltage [Vin]. This is the same operation as at time T0, and the operation from time T0 to T4 is repeated. Here, the first to fourth
Switching elements 121a, 122a, 123a, 1
At 24a, the respective ON periods are equal, and T1−T0 = T3.
−T2 = Ton, and each off period is equal to T2−T1
= T4-T3 = Toff The on / off ratio of each switching element is set. With this setting, in the stable operation state, the third inductor 16
3 turns on the first switching element 121a and then returns to the first switching element 121a again.
Returns to the initial state in one turn-on period, and thus has the relationship of the following equation (1).

(Vin / n−Vout) × Ton−Vout × Toff = 0 (1)

Therefore, the output voltage [Vout] has a relationship with the input voltage [Vin] according to the following equation (2).

Vout = δ × Vin / n (2)

Where δ in equation (2) is the following equation (3)
Indicated by

Δ = Ton / (Ton + Toff) ------ (3)

That is, the output voltage [Vout] varies from the first to fourth switching elements 121a, 122a, 123
It can be stabilized by adjusting the on / off ratios at the points a and 124a. In this conventional full-bridge converter, the first to fourth switching elements 121
In a, 122a, 123a, and 124a, the current flows in a well-balanced manner, so that there was a feature that the application of the present invention to a small-sized and high-power power supply device was easy due to the dispersion of stress.

[0016]

However, in the above-described conventional full-bridge converter, the charge and discharge of the parasitic capacitor occur instantaneously when the first to fourth switching elements 121a, 122a, 123a, and 124a are turned on. An electric current has occurred. There has been a problem that the surge current causes power loss and noise in the conventional full-bridge converter. Further, the first to fourth switching elements 121a, 122a, 123
At the time of turn-off at a and 124a, an unnecessary resonance voltage was generated due to the leakage inductance of the transformer and the parasitic inductance of the wiring. The conventional full-bridge converter has a problem that power loss and noise occur even by the unnecessary voltage resonance. The present invention
It is an object of the present invention to provide a switching power supply device that achieves high efficiency and low noise by reducing unnecessary surge current and resonance voltage due to a parasitic capacitor and a leakage inductance over a wide load range.

[0017]

In order to achieve the above object, a switching power supply according to the present invention has first switching means and second switching means which alternately turn on and off with a dead time period. A first series circuit connected to the input DC power supply; and a third switching means and a fourth switching means that alternately turn on and off with a dead time period, and are connected to the input DC power supply. A second series circuit, a transformer having at least a primary winding and a secondary winding, a first terminal of a primary winding of the transformer, the first switching means, and the second switching. A first inductor connected between the connection points of the first and second means, a second terminal of the primary winding of the transformer, and a connection point between the third switching means and the fourth switching means. Contact And, and said first inductor and a second inductor magnetically coupled, the transformer 1
A first diode connected between a first terminal of a secondary winding and a negative electrode or a positive electrode of the input DC power supply, and a negative electrode that is the same as the second terminal of the primary winding of the transformer and the first diode; A second diode connected between the positive electrode, a rectifying and smoothing means for rectifying and smoothing a voltage induced in a secondary winding of the transformer, and an F which constitutes the first switching means.
On / off control for controlling the duty ratio of a controllable switching element such as an ET or IGBT, or the duty ratio of a controllable switching element such as an FET or an IGBT constituting the third switching means, or a ratio of both. Means.

According to this switching power supply device, the parasitic capacitor of each switching means can be charged / discharged by the energy stored in the inductor, and each switching means can be turned on with substantially zero voltage. Therefore, generation of a surge-like short-circuit current can be prevented or reduced, and efficiency can be improved and noise can be suppressed. Further, when it is necessary to cope with a light load, the parasitic capacitor of each switching means can be sufficiently charged and discharged by increasing the inductance value of the inductor and increasing the energy stored in the inductor. Therefore, as described above, the occurrence of short-circuit current can be prevented or reduced, and the efficiency can be improved and the generation of noise can be suppressed.

Further, in the present invention, the two inductors are magnetically coupled to each other, so that unnecessary resonance with the parasitic capacitor of the transformer due to supplementing the inductors does not occur. As a result, high efficiency and low noise can be achieved over a wide load range. In the switching power supply device configured as described above, the first switching unit, the second switching unit,
It is preferable that each of the third switching means and the fourth switching means is constituted by a controllable switching element including a parallel diode or a parallel connection of a controllable switching element and a diode.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a switching power supply according to the present invention will be described below with reference to the accompanying drawings.

First Embodiment A switching power supply according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a first embodiment according to the present invention.
FIG. 2 is a circuit diagram showing a configuration of a switching power supply device of FIG. In FIG. 1, the first switching means 21 is configured by connecting a first switching element 21a, a diode 21b, and a capacitor 21c in parallel. Capacitor 2
1c is the first switching element 21a and the diode 2
1b. The second switching means 22 includes a second switching element 22a.
And a diode 22b and a capacitor 22c connected in parallel. The capacitor 22c is a capacitor parasitically present in the second switching element 22a and the diode 22b. First switching element 21a
And the second switching element 22a have a dead time period so that the control circuit 7 turns on and off alternately and complementarily.
1 is controlled by a control signal. The allowable range of the dead time period differs depending on the design method and the operation state of each switching power supply device. Also, the first switching means 21 and the second switching means 22
Are connected in series and connected between the input terminals 12a and 12b. The input DC power supply 11 has an input terminal 12a,
12b.

Similarly, the third switching means 23
The third switching element 23a, the diode 23b, and the capacitor 23c are connected in parallel. The capacitor 23c is a capacitor parasitically present in the third switching element 23a and the diode 23b.
The fourth switching means 24 is configured by connecting a fourth switching element 24a, a diode 24b, and a capacitor 24c in parallel. The capacitor 24c is connected to the fourth
Are parasitically present in the switching element 24a and the diode 24b. The third switching element 23a and the fourth switching element 24a have a dead time period, and are controlled by a control signal from the control circuit 71 to alternately turn on and off alternately. The allowable range of the dead time period differs depending on the design method and the operation state of each switching power supply device. Further, the third switching means 23 and the fourth switching means 24 are connected in series and are connected between the input terminals 12a and 12b. The switching element in each switching means is constituted by a controllable switching element such as an FET or an IGBT.

The ON timing and the OFF timing of the third switching element 23a are controlled by being shifted by a half cycle from the ON timing and the OFF timing of the first switching element 21a, respectively. The transformer 31 is
It has a primary winding 31a, a first secondary winding 31b, and a second secondary winding 31c, and has a primary winding 31a and a first secondary winding 3
The turn ratio between 1b and the second secondary winding 31c is n: 1: 1. A first terminal of the primary winding 31a is connected to a connection point between the first switching means 21 and the second switching means 22 via a first inductor 41a. The second terminal of the primary winding 31a is connected to a connection point between the third switching means 23 and the fourth switching means 24 via a second inductor 41b. First inductor 41a and second inductor 41b
Are magnetically coupled. Also, the first inductor 4
In 1a and the second inductor 41b, the number of turns is the same, and the inductance value is sufficiently smaller than the inductance value of the primary winding 31a of the transformer 31.

The cathode of the diode 51 is connected to the transformer 3
The first terminal of the primary winding 31a is connected to the first terminal, and the anode of the diode 51 is connected to the input terminal 12b.
The cathode of the diode 52 is connected to the second terminal of the primary winding 31a of the transformer 31, and the anode of the diode 52 is connected to the input terminal 12b. Diode 6
1 is connected to the first secondary winding 31b of the transformer 31.
Are connected to the first terminal of The anode of the diode 62 is connected to the second terminal of the second secondary winding 31c of the transformer 31. The second terminal of the first secondary winding 31b of the transformer 31 is connected to the first terminal of the second secondary winding 31c. The cathodes of the diode 61 and the diode 62 are connected to each other.
The third inductor 63 and the smoothing capacitor 64 are connected in series, the interconnection point between the cathodes of the diodes 61 and 62, the second terminal of the first secondary winding 31b, and the second secondary winding. It is connected between the connection point of the first terminal 31c.

The transformer 31 includes diodes 61 and 62, a third inductor 63, and a smoothing capacitor 64.
Can be obtained by rectifying and smoothing the voltage generated in the first secondary winding 31b and the second secondary winding 31c. A load 66 is connected between the output terminals 65a and 65b. The control circuit 71 detects a voltage between the output terminals 65a and 65b, and controls the first so that the DC output voltage becomes constant.
To the fourth switching elements 21a, 22a, 23a,
A control signal for controlling the ON / OFF of each of 24a is generated.

Next, the operation of the switching power supply according to Embodiment 1 will be described with reference to FIG. FIG. 2 is an operation waveform diagram of each unit in the switching power supply device according to the first embodiment. In the waveform diagram shown in FIG. 2, times T0 to T8 are shown in the figure to show the temporal change of each operation state. G1, G2, G3 and G4 shown in FIG. 2 are first to fourth switching elements 21a, 22a and 23.
a and 24a are shown. FIG.
, V22 indicates a voltage waveform applied to the second switching means 22, V24 indicates a voltage waveform applied to the fourth switching means 24, and V3
1a shows a voltage waveform applied to the primary winding 31a of the transformer 31. In FIG. 2, I31a indicates a current waveform flowing through the primary winding 31a of the transformer 31, I21 indicates a current waveform flowing through the first switching unit 21, and I22 indicates a second switching unit 22. 3 shows a waveform of a current flowing through the circuit. I51 indicates the current flowing through the diode 51, I52 indicates the current flowing through the diode 52, and V41b indicates the second inductor 41b.
3 shows a waveform of a voltage applied to.

At time T0, when the voltage applied to the first switching means 21 reaches zero, the diode 21b
Turns on. While the diode 21b is on, the first switching element 21a is turned on by the control signal G1 of the control circuit 71. At this time, the first
Current flowing through the switching means 21 of the diode 2
There is no significant difference in operation whether the current flows to 1b or the first switching element 21a. Each voltage V41 of the first inductor 41a and the second inductor 41b is passed through the fourth switching element 24a which is already turned on.
a, V41b decrease from the input voltage [Vin] to zero, and the voltage V31a of the primary winding 31a of the transformer 31 becomes the input voltage [Vin]. Primary winding 31 of transformer 31
a of the transformer 31 becomes the input voltage [Vin], the first secondary winding 31 b and the second secondary winding 3
1c are voltages [Vi]
n / n]. At this time, the diode 61 is turned on and the diode 62 is turned off. Third inductor 63
Becomes the voltage [Vin / n-Vout].
The current flowing through the third inductor 63 increases linearly. The current I31a of the primary winding 31a of the transformer 31 is
Since it is the sum of the primary-side converted current of the exciting current of the transformer 31 and the current flowing through the third inductor 63, it increases linearly. The primary-side converted current is obtained by converting a current flowing through the third inductor 63 into a current flowing through the primary winding 31a. At this time, the control circuit 71 turns off the second switching element 22a, and turns off the third switching element 23.
a is turned off, and the fourth switching element 24a is turned on. Therefore, the diode 21b and the diode 24b are short-circuited by the first switching element 21a and the fourth switching element 24a, respectively. The diode 22b and the diode 23b are reverse-biased and turned off.

At time T1, when the fourth switching element 24a is on, the control signal G
Due to 1, the first switching element 21a is turned off. At this time, the current flowing through the primary winding 31a of the transformer 31 does not change abruptly under the influence of the current flowing through the third inductor 63. Therefore, the capacitor 21
c, 22c are charged and discharged, and the second switching means 22
Is gradually reduced. Control circuit 7
1 is the second switching element 2 during the period from when the first switching element 21a is turned off to when it is detected that the voltage applied to the second switching means 22 has become zero.
2a is set not to be turned on.

At time T2, when the voltage applied to the second switching means 22 reaches zero, the diode 22b
Turns on. While the diode 22b is on, the control circuit 71 turns on the second switching element 22a by the control signal G2. At this time, the second
The current flowing through the switching means 22 is
There is no significant difference in the operation whether the current flows through b or the second switching element 22a. Also, through the diode 22b or the second switching element 22a that is on and the fourth switching element 24a that is already on,
Primary winding 31a of transformer 31 and first inductor 41
The series circuit of a and the second inductor 41b is short-circuited. For this reason, the primary winding 31a of the transformer 31 and the first
And the second inductor 41b are short-circuited at both ends. Therefore, the sum of the energy stored in the first inductor 41a and the energy stored in the second inductor 41b is maintained. At this time, the first secondary winding 31b and the second secondary winding 31 of the transformer 31
The voltage induced at c is zero. This will be described in more detail. The voltage V3 induced in the first secondary winding 31b of the transformer 31 by the influence of the on-voltage of each diode.
1b is slightly positive, the second secondary winding 31 of the transformer 31
The voltage V31c induced in c becomes slightly negative. The current of the secondary winding of the transformer 31 is equal to the first secondary winding 3.
Flow to 1b. The voltage V63 applied to the third inductor 63 becomes the voltage [−Vout], and the flowing current decreases linearly.

FIG. 3A is a circuit diagram illustrating a change in the current flowing through the second inductor 41b during a period from time T1 to time T3 when the fourth switching element 24a is turned off. FIG. 3 (b) is a view similar to FIG.
FIG. 7 is a waveform diagram showing details of a current flowing through the second inductor 41b and the diode 52 during a period from time T1 to T3 in the circuit shown in FIG. Assuming that the currents flowing through the coupled first inductor 41a and the second inductor 41b are I41a and I41b, respectively, and the inductance values of the first inductor 41a and the second inductor 41b are both L41, the first coupled inductor 41a The sum E41 of the energy stored in the inductor 41a and the second inductor 41b is expressed by the following equation (4).

[0031] E41 = L41 × (I41a + I41b ) 2/2 ------ (4)

During a period from time T1 when the first switching element 21a turns off to time T2 when the voltage applied to the second switching means 22 reaches zero and the diode 22b turns on, the first inductor 41a and the second inductor 41a are turned on. The same current flows through the inductor 41b. Also,
In this period, the second switching means 22 and the first
The capacitor 22c and the capacitor 21c included in each of the switching means 21 are charged and discharged. When the charging voltage of the capacitor 22c becomes zero, the diode 22b turns on. The sum E411 of the energy stored in the first inductor 41a and the second inductor 41b when the diode 22b is turned on is equal to the sum of the energy stored in the diode 22b.
When the current flowing through the first inductor 41a and the second inductor 41b immediately before the turn-on of is represented by IP, the current is expressed as the following equation (5). While the diode 22b is on, the first inductor 41a and the second inductor 41b are short-circuited at both ends as described above. Therefore, the first inductor 41a and the second inductor 41a
E41 of the energy stored in the inductor 41b
1 is held.

[0033] ^{E411 = L41 × (IP × 2} ) 2/2 ------ (5)

When the diode 22b is turned on, the current I31a flowing through the primary winding 31a of the transformer 31 becomes a primary-side converted current of the current flowing through the third inductor 63.
Therefore, the current I31a decreases linearly. Current I41a flowing through first inductor 41a is limited to current I31a flowing through primary winding 31a of transformer 31. The current I41b flowing through the second inductor 41b includes the first inductor 41 just before the diode 22b is turned on.
The current of the following formula (6) flows so as to keep the sum of the current a and the current IP flowing through the second inductor 41b constant.

I41b = IP × 2-I31a (6)

The current flows as described above,
The current I41a flowing through the inductor 41a and the current I41b flowing through the second inductor 41b satisfy the relationship of the following equation (7).

I41a + I41b = IP × 2 (7)

Therefore, the sum of the current I41a flowing through the first inductor 41a and the current I41b flowing through the second inductor 41b becomes constant. As a result, the energy E
411 is kept constant. Therefore, as shown in FIG. 3B, the current I41 flowing through the second inductor 41b
The current I52 flowing through the diode b and the diode 52 has a current waveform having the above-described current component. In the current waveform diagram (I41b) shown in FIG. 3B, a region indicated by a thin vertical line indicates a current component I flowing through the primary winding 31a of the transformer 31.
31a is shown. Further, in FIG. 3B, a region indicated by a thin oblique line indicates a current I52 flowing through the diode 52.
It is. That is, the current I52 is a current component obtained by removing the current I31a from the current I41b flowing through the second inductor 41b, and can be expressed by the following equation (8).

I52 = I41b-I31a = (IP × 2-I31a) −I31a = IP × 2-I31a × 2 (8)

At time T3 shown in FIG. 2, when the fourth switching element 24a is turned off, the capacitors 23c and 24c are charged by the energy held in each of the first inductor 41a and the second inductor 41b. Discharge. Therefore, the voltage applied to the third switching means 23 gradually decreases. The control circuit 71 sets so that the third switching element 23a is not turned on during a period from when the fourth switching element 24a is turned off to when it is detected that the voltage applied to the third switching means 23 becomes zero. I have. Time T
In 4, when the voltage applied to the third switching means 23 reaches zero, the diode 23b is turned on.
While the diode 23b is on, the control circuit 7
1 is the third switching element 23a according to the control signal G3.
Turn on. At this time, there is no significant difference in the operation whether the current flowing through the third switching means 23 flows through the diode 23b or the third switching element 23a.

When the third switching element 23a is turned on, the voltage applied to the first inductor 41a and the second inductor 41b is reduced to zero through the second switching element 22a that is already on, and the voltage of the transformer 31 is reduced. The voltage V31a applied to the primary winding 31a becomes the voltage [-Vin]. Primary winding 31a of transformer 31
The voltage [-Vin] is applied to the voltage V31a of the second secondary winding 31 and the voltage V31b of the first secondary winding 31b.
Both the voltage VV31c of c becomes the voltage [−Vin / n]. As a result, the diode 61 is turned off, and the diode 62 is turned off.
Turns on. Therefore, the voltage V of the third inductor 63
63 becomes the voltage [Vin / n-Vout], and the current flowing through the third inductor 63 increases linearly.

The current I3 of the primary winding 31a of the transformer 31
Since 1a is the sum of the exciting current of the transformer 31 and the primary-side converted current of the current flowing through the third inductor 63, the absolute value linearly increases. Therefore, the third inductor 63 stores the excitation energy. At this time, the control circuit 71 controls to turn off the first switching element 21a, turn on the second switching element 22a, and turn off the fourth switching element 24a. Therefore, the diode 22b and the diode 23b are short-circuited by the second switching element 22a and the third switching element 23a, respectively,
b and the diode 24b are reverse-biased and turned off.

At time T5, when the second switching element 22a is on, the control signal G
Due to 3, the third switching element 23a is turned off. At this time, the current I31a flowing through the primary winding 31a of the transformer 31 does not change rapidly due to the influence of the current flowing through the third inductor 63. Therefore, the capacitors 23c and 24c charge and discharge, and the voltage V24 applied to the fourth switching means 24 gradually decreases. The control circuit 71 controls the third switching element 23
The setting is made so that the fourth switching element 24a is not turned on during a period from when a is turned off to when it is detected that the voltage applied to the fourth switching means 24 becomes zero.

At time T6, when the voltage applied to the fourth switching means 24 reaches zero, the diode 24b
Turns on. While the diode 24b is on, the control circuit 71 turns on the fourth switching element 24a by the control signal G4. At this time, the current flowing through the fourth switching means 24 is the diode 24b.
And the flow through the fourth switching element 24a, there is no significant difference in operation.

The transformer 3 is connected to the diode 24b or the fourth switching element 24a which is turned on and the second switching element 22a which is already turned on.
The series circuit of the first primary winding 31a, the first inductor 41a, and the second inductor 41b is short-circuited. Therefore, both ends of the primary winding 31a of the transformer 31, the first inductor 41a, and the second inductor 41b are short-circuited. Therefore, the sum of the energy stored in the first inductor 41a and the energy stored in the second inductor 41b is maintained. The operation from time T5 to time T7 when the second switching element 22a is turned off is the same as that between time T1 and time T3 described above.

The voltages V31b, V31 induced in the first secondary winding 31b and the second secondary winding 31c of the transformer 31
c becomes zero, and the voltage V63 applied to the third inductor 63 becomes the voltage [−Vout]. A current flows through the second secondary winding 31c of the transformer 31 so as to keep the excitation energy of the third inductor 63 continuous. Time T
7, when the second switching element 22a is turned off, the capacitors 21c and 22c are charged and discharged by the energy held in the first inductor 41a and the second inductor 41b. As a result,
The voltage applied to the first switching means 21 gradually decreases. The control circuit 71 does not turn on the first switching element 21a during a period from when the second switching element 22a is turned off to when it is detected that the voltage applied to the first switching means 21 becomes zero. Is set to

At time T8, when the voltage applied to the first switching means 21 reaches zero, the diode 21b
Turns on. The circuit operation from time T8 is time T0
Is the same as the operation of the circuit from FIG. As described above, in the switching power supply according to Embodiment 1, the on / off operation is repeatedly performed.

In the first embodiment, the second
, The period from time T3 to the time when the third switching element 23a is turned on, the time from time T5 to the time when the fourth switching element 24a is turned on, and the time from time T7 to the first switching. Since the period until the element 21a is turned on is short, it is ignored.
Further, the ON period of the first switching element 21a and the third period
The on-period of the switching element 23a is equal to Ton. An off period from when the first switching element 21a is turned off to when the third switching element 23a is turned on, and an off period from when the third switching element 23a is turned off to when the first switching element 21a is turned on. Are equally Toff. In the first embodiment, as is apparent from FIG. 2, the first switching element 21a and the third switching element 23a
Is set to 50% or less.

In the stable operation state, the magnetic flux of the third inductor 63 is changed to the first switching element 2 when the turn-on of the first switching element 21a is set to the initial state.
Since the first switching element 121a returns to the initial state one cycle after the first switching element 121a is turned on after the first element 1a is turned on, the following equation (9) holds.

(Vin / n−Vout) × Ton−Vout × Toff = 0 (9)

Accordingly, the output voltage [Vout] has a relationship with the input voltage [Vin] according to the following equation (10).

Vout = δ × Vin / n (10)

Where δ in equation (10) is the following equation (1)
This is indicated by 1).

Δ = Ton / (Ton + Toff) ------ (11)

Therefore, in the switching power supply of the first embodiment, the output voltage [Vo is determined by the on / off ratio of the first switching element 21a and the third switching element 23a.
ut] can be controlled. For this reason, the switching power supply of the first embodiment is of the same conversion type as the conventional full-bridge converter. In the switching power supply of the first embodiment, as described above, the period from time T1 to the time when the second switching element 22a is turned on, the time from time T3 to the time when the third switching element 23a is turned on, and time T5. From the time T7 until the fourth switching element 24a is turned on.
, And the current flowing in the reverse direction immediately after the first to fourth switching elements 21a, 22a, 23a, 24a are turned on is ignored. Also, taking into account other neglected points, the output voltage is calculated by the above equation (1).
0). However, it is possible to easily compensate for the decrease in the output voltage by setting δ to be large. Therefore, a predetermined output voltage can be obtained by the switching power supply of the first embodiment configured as described above.

The switching power supply according to the first embodiment
First to fourth switching elements 21a, 22a, 23
Immediately before the turn-on of the switching elements a and 24a, the capacitors 21c, 22c,
It is configured to turn on after discharging 23c and 24c using the energy stored in the first inductor 41a and the second inductor 41b. For this reason,
The switching power supply device according to the first embodiment can greatly reduce a surge-like short-circuit current, improve efficiency, and suppress generation of noise. Further, in the switching power supply device according to the first embodiment, when it is necessary to cope with a light load, the inductance values of first inductor 41a and second inductor 41b are increased to store the respective inductors. The energy is increased so that the parasitic capacitor of each switching means can be charged and discharged sufficiently. As a result, the switching power supply of the first embodiment can improve the efficiency and suppress the generation of noise even under a light load.

In the case of the prior art, the first inductance depends on the leakage inductance of the transformer and the parasitic inductance of the wiring.
To the fourth switching elements 121a, 122a, 12
There is a problem that an unnecessary resonance voltage is generated when the 3a and 124a (see FIG. 6) are turned off. However, in the switching power supply of the first embodiment, the resonance voltage is clamped by turning on the diodes 22b, 21b, 24b, and 23b in response to the turning off of each switching element. Immediately after that, the second switching element 22a, the first switching element 21a, the fourth switching element 24a, and the third switching element 23a connected in parallel are turned on, so that the voltage clamp is maintained. Therefore, in the switching power supply of the first embodiment, unnecessary resonance voltage does not occur.

Next, a full bridge converter will be considered. Japanese Patent Application Laid-Open No. 11-89232 discloses a switching power supply device having a configuration in which an inductor is added in series to a primary winding of a transformer. In the switching power supply having such a configuration, an unnecessary resonance voltage between a parasitic capacitor of the transformer and a primary capacitor of the transformer and an additional inductor is generated at a connection point, and a resonance current flows. It is considered to be. On the other hand, in the case of the switching power supply of the first embodiment, the first inductor 4
The current due to the energy stored by the first inductor 41a and the second inductor 41b is, because the first inductor 41a and the second inductor 41b are magnetically coupled, the second switching means 22 and the diode 52, or
The current is divided by the fourth switching means 24 and the diode 51, and the voltage across the transformer is substantially fixed to zero. Therefore, even if a parasitic capacitor exists in the transformer 31, the first inductor 41 a and the second inductor 4
Unnecessary resonance with 1b does not occur.

In the switching power supply device of the first embodiment, the first switching element 21a is turned off and the second switching element 22a is turned on, and the first switching element 22a is turned off and the first switching element 22a is turned off. During the period until the third switching element 23a is turned off and the fourth switching element 24a is turned on, the third switching element is turned off after the fourth switching element 24a is turned off. The period until 23a is turned on is set using a method of detecting the voltage applied to the first to fourth switching means.
The present invention is not limited to such a setting method. For example, a method of detecting and setting a current flowing through a diode connected in parallel to the first to fourth switching elements may be used, or a predetermined time may be used. Needless to say, the period can be set by setting.

In the first embodiment, the first to fourth switching elements 21a, 22a, 23a, 24
a parasitically connected capacitor 21 a
In addition to c, 22c, 23c, and 24c, it is also possible to add an external capacitor in order to further reduce the noise component by making the voltage change more gentle. Even with such a configuration, there is no significant difference from the first embodiment in the basic operation. Further, the capacitor 21c,
Although 22c, 23c, and 24c are parasitic capacitors of switching elements and diodes arranged in parallel, it is obvious that floating capacitors included in a circuit pattern can be considered. As described above, according to the first embodiment, it is possible to provide a switching power supply device capable of achieving high efficiency and low noise over a wide load range.

Second Embodiment Next, a switching power supply according to a second embodiment of the present invention will be described with reference to FIGS.
This will be described with reference to FIG. FIG. 4 is a circuit diagram showing a configuration of the switching power supply according to Embodiment 2 of the present invention. FIG.
FIG. 7 is a waveform diagram for explaining an operation in the switching power supply device according to the second embodiment. In the switching power supply device according to the second embodiment, portions having the same functions and configurations as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

The switching power supply according to the second embodiment
As shown in FIG. 4, compared to the switching power supply of the first embodiment shown in FIG.
2 is deleted, and diodes 53 and 54 are inserted instead. As shown in FIG. 4, the anode of the diode 53 according to the second embodiment is connected to the first terminal of the primary winding 31a of the transformer 31, and the cathode of the diode 53 is connected to the input terminal 12a. Diode 5
4 is connected to the second winding of the primary winding 31a of the transformer 31.
, And the cathode of the diode 54 is connected to the input terminal 12a.

In the operation waveform diagram of the switching power supply device of the second embodiment shown in FIG. 5, the waveforms of the same circuit components as those of the operation waveform diagram of FIG. Description is omitted. In FIG. 5, I53 indicates a waveform of a current flowing through the diode 53, and I54 indicates a current of the diode 54.
2 shows a waveform of a current flowing through.

In the switching power supply of the second embodiment shown in FIG. 4, the control signal G1 output from the control circuit 71 and the on / off operation of the first switching means 21 are the same as those of the first embodiment. This is equivalent to the control signal G2 output from the control circuit 71 in the power supply device and the on / off operation of the second switching means 22. The control signal G2 output from the control circuit 71 and the on / off operation of the second switching means 22 are controlled by the control signal G1 output from the control circuit 71 and the first control signal G1 in the switching power supply of the first embodiment. Switching means 21
Is equivalent to the on / off operation of Also, the control signal G3 output from the control circuit 71 and the third switching means 23
The on / off operation is the same as the control signal G4 output from the control circuit 71 and the on / off operation of the fourth switching means 24 in the switching power supply of the first embodiment. Further, the control signal G4, which is the output of the control circuit 71, and the operation of the fourth switching means 24 are based on the control signal G3, which is the output of the control circuit 71 in the switching power supply of the first embodiment, and the third switching means. 23 is equivalent to the on / off operation.

The diode 5 according to the second embodiment
The operations of the diode 3 and the diode 54 are the same as the operations of the diode 51 and the diode 52 in the switching power supply of the first embodiment. The operation of the transformer 31 and the diodes 61 and 62 according to the second embodiment is the same as the operation of the transformer 31 and the diodes 61 and 62 in the switching power supply according to the first embodiment except that the phase of the voltage / current is inverted by 180 °. The operation of the other circuit portions in the switching power supply of the second embodiment is the same as that of the first embodiment.

Hereinafter, the output voltage in the second embodiment will be discussed. In the switching power supply device according to the second embodiment, a period from time T1 to when first switching element 21a is turned on, a period from time T3 to when fourth switching element 24a is turned on, and a third switching element from time T5. A period until the second switching element 22a is turned on and a period until the second switching element 22a is turned on from the time T7 are short and are ignored. Further, the ON period of the second switching element 22a and the ON period of the fourth switching element 24a are set to Ton. An off period from when the second switching element 22a turns off to when the fourth switching element 24a turns on, and an off period from when the fourth switching element 24a turns off to when the second switching element 22a turns on. Are equally Toff. In the second embodiment, as shown in FIG. 5, the duty ratio of the second switching element 22a and the fourth switching element 24a is set to 50% or less. The relationship between the output voltage and the input voltage in the second embodiment has the same relationship as Expression (10) indicating the output voltage [Vout] and the input voltage [Vin] described in the first embodiment. .

Next, the diode 5 according to the second embodiment will be described.
3 and 54 are the diodes 51 and 5 shown in the first embodiment.
2, the reason why both ends of the transformer 31 are connected to the input terminal 12a connected to the positive terminal of the input DC power supply will be briefly described. In the first embodiment, as shown in FIG. 3, there is a period in which the second switching means 22 and the fourth switching means 24 connected to the input terminal 12b are simultaneously turned on. During that period, the second switching means 22, the inductor 41a, and the
The next winding 31a, the inductor 41b coupled to the inductor 41a, and the fourth switching means 24 form a loop. The current flowing through this loop is limited by the current flowing through the primary winding 31a of the transformer 31. In order to maintain the energy of the coupled inductors 41a and 41b, a portion of the current flowing through the inductors 41a and 41b that exceeds the current flowing through the primary winding 31a of the transformer 31 is the inductor 41a or the inductor 4a.
1b is flowed by short-circuiting both ends. Therefore, the first embodiment
In the above, the diodes 51 and 52 are connected between the terminals of the inductors 41a and 41b and the input terminal 12b, respectively, to perform a desired operation.

On the other hand, in the second embodiment, the first switching means 21 connected to the input terminal 12a and the third
There is a period during which the switching means 23 are simultaneously turned on. In that period, the first switching means 21,
The inductor 41a, the primary winding 31a of the transformer 31, the inductor 41b coupled to the inductor 41a, and the third switching means 23 form a loop. The current flowing through this loop is limited by the current flowing through the primary winding 31a of the transformer 31. Coupled inductor 41
In order to hold the energy of the inductors 41a and 41b, the portion of the current flowing through the inductors 41a and 41b that exceeds the current flowing through the primary winding 31a of the transformer 31 is short-circuited between both ends of the inductor 41a or the inductor 41b. And flow Therefore, the inductors 41a, 41
Shorting means is required between the terminal b and the input terminal 12a, and the diodes 53 and 54 are inserted as the shorting means in the second embodiment.

The switching power supply according to the second embodiment
As in the switching power supply of the first embodiment, first to fourth switching elements 21a, 22a, 23a,
Immediately before the turn-on of 4a, capacitors 21c, 22c, and 23 that are parasitically present in each switching element.
c and 24c are discharged using the energy stored in the first inductor 41a and the second inductor 41b, and then turned on. Therefore, the surge-like short-circuit current can be significantly reduced, and the efficiency can be improved and the generation of noise can be suppressed. In the switching power supply according to the second embodiment, when it is necessary to cope with a light load, the first
By setting the inductance values of the inductor 41a and the second inductor 41b to be large, the energy stored in the inductors is increased, and the parasitic capacitors of each switching means can be charged and discharged sufficiently. As a result, the switching power supply according to the second embodiment can improve efficiency and suppress generation of noise even under a light load. Further, in the switching power supply device according to the second embodiment, generation of an unnecessary resonance voltage due to the leakage inductance of the transformer and the parasitic inductance of the wiring is prevented.

Next, a full bridge converter will be considered. Japanese Patent Application Laid-Open No. 11-89232 discloses a switching power supply device having a configuration in which an inductor is added in series to a primary winding of a transformer. In the switching power supply having such a configuration, an unnecessary resonance voltage between a parasitic capacitor of the transformer and a primary capacitor of the transformer and an additional inductor is generated at a connection point, and a resonance current flows. It is considered to be. On the other hand, in the case of the switching power supply of the second embodiment, the first inductor 4
The current due to the energy stored by the first inductor 41a and the second inductor 41b is, because the first inductor 41a and the second inductor 41b are magnetically coupled, the first switching means 21 and the diode 54, or
The current is divided by the third switching means 23 and the diode 53. Then, the voltage across the transformer is fixed to substantially zero. For this reason, even if a parasitic capacitor exists in the transformer 31, unnecessary resonance with the first inductor 41a and the second inductor 41b does not occur.

In the switching power supply according to the second embodiment, during the period from when the first switching element 21a is turned off to when the second switching element 22a is turned on, the first switching element 22a is turned off and then the first switching element 22a is turned off. During the period until the third switching element 23a is turned off and the fourth switching element 24a is turned on, the third switching element is turned off after the fourth switching element 24a is turned off. The period until 23a is turned on is set using the method of detecting the voltage applied to the first to fourth switching means, as in the first embodiment. The present invention is not limited to such a setting method. For example, a method of detecting and setting a current flowing through a diode connected in parallel to the first to fourth switching elements may be used, or a predetermined time may be used. Is set, the period can be set.

In the second embodiment, the first to fourth switching elements 21a, 22a, 23a, 24
a parasitically connected capacitor 21 a
In addition to c, 22c, 23c, and 24c, it is also possible to add an external capacitor in order to further reduce the noise component by making the voltage change more gentle. Even with such a configuration, there is no significant difference from the first embodiment in the basic operation. Further, the capacitor 21c,
Although 22c, 23c, and 24c are parasitic capacitors of switching elements and diodes arranged in parallel, it is obvious that floating capacitors included in a circuit pattern can be considered. As described above, according to the second embodiment, it is possible to provide a switching power supply device capable of achieving high efficiency and low noise over a wide load range.

[0073]

As apparent from the detailed description of the specific embodiments, the present invention has the following effects. In the switching power supply according to the present invention, immediately before the first to fourth switching units are turned on, the capacitors that are parasitically present in the respective switching units are stored in the first inductor and the second inductor that are coupled. It is configured to be turned on after charging and discharging using energy. Therefore, according to the present invention, it is possible to obtain a switching power supply device capable of preventing the occurrence of a surge-like short-circuit current or reducing the short-circuit current, improving the efficiency, and suppressing the generation of noise.

In the switching power supply of the present invention, the efficiency can be improved and the generation of noise can be suppressed over a wide load range by setting the respective inductance values of the first inductor and the second inductor to be large. It is. In the switching power supply of the present invention, the diodes connected in parallel to the respective second, first, fourth, and third switching elements are turned on when the first to fourth switching elements are turned off. Causes the resonance voltage to be clamped. Immediately thereafter, the switching power supply of the present invention maintains the voltage clamp by turning on the second, first, fourth, and third switching elements connected in parallel, and generates an unnecessary resonance voltage. I will not do it.

Also, in the switching power supply of the present invention, the current due to the energy stored by the first inductor and the second inductor is magnetically coupled between the first inductor and the second inductor. The current flows through the second switching element and the second diode, and flows through the fourth switching element and the first diode. This allows
According to the present invention, it is possible to realize a switching power supply device in which unnecessary resonance between the first and second inductors and the parasitic capacitor of the transformer does not occur and high efficiency and low noise can be achieved over a wide load range. .

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a switching power supply according to Embodiment 1 of the present invention.

FIG. 2 is a waveform chart showing the operation of each unit in the switching power supply according to Embodiment 1 of the present invention.

FIG. 3A is an explanatory diagram showing operations of a first inductor and a second inductor in the switching power supply according to the first embodiment of the present invention; (B) A current waveform diagram flowing through the second diode and the fourth switching means in the switching power supply according to the first embodiment of the present invention.

FIG. 4 is a circuit diagram showing a configuration of a switching power supply device according to Embodiment 2 of the present invention.

FIG. 5 is a waveform chart showing the operation of each unit in the switching power supply according to Embodiment 2 of the present invention.

FIG. 6 is a circuit diagram showing a configuration of a conventional full-bridge converter.

FIG. 7 is a waveform chart showing the operation of each unit in a conventional full-bridge converter.

[Explanation of symbols]

 11 Input DC Power Supply 12a, 12b Input Terminal 21 First Switching Means 21a First Switching Element 21b Diode 21c Capacitor 22 Second Switching Means 22a Second Switching Element 22b Diode 22c Capacitor 23 Third Switching Means 23a Third Switching element 23b diode 23c capacitor 24 fourth switching means 24a fourth switching element 24b diode 24c capacitor 31 transformer 31a primary winding 31b first secondary winding 31c second secondary winding 41a first Inductor 41b Second inductor 51 Diode 52 Diode 53 Diode 54 Diode 61 Diode 62 Diode 63 Third inductor 64 Smoothing capacitor 65a, 6 5b output terminal 66 load 71 control circuit

Claims (12)

[Claims] 1. A first series circuit connected to an input DC power supply, comprising a first switching means and a second switching means which are alternately turned on and off with a dead time period, and have a dead time period. And a third switching means and a fourth switching means which are alternately turned on and off,
A second series circuit connected to the input DC power supply, a transformer having at least a primary winding and a secondary winding, a first terminal of a primary winding of the transformer, and the first switching means. A first inductor connected between a connection point of the second switching means, a second terminal of a primary winding of the transformer, and a connection point of the third switching means and the fourth switching means; And a second inductor magnetically coupled with the first inductor, connected between a first terminal of a primary winding of the transformer and a negative electrode of the input DC power supply. A first diode, a second diode connected between a second terminal of a primary winding of the transformer and a negative electrode of the input DC power supply, and a rectifier smoothing voltage induced in a secondary winding of the transformer. Rectifying and smoothing means, and On / off control means for controlling a duty ratio of a controllable switching element included in the first switching means, a duty ratio of a controllable switching element included in the third switching means, or a ratio of both. A switching power supply device comprising: 2. The switching power supply device according to claim 1, wherein each of the controllable switching elements included in the first switching means and the third switching means has a duty ratio of 50% or less. 3. A first series circuit connected to an input DC power supply, comprising a first switching means and a second switching means which are turned on and off alternately with a dead time period, and have a dead time period. And a third switching means and a fourth switching means which are alternately turned on and off,
A second series circuit connected to the input DC power supply, a transformer having at least a primary winding and a secondary winding, a first terminal of a primary winding of the transformer, and the first switching means. A first inductor connected between a connection point of the second switching means, a second terminal of a primary winding of the transformer, and a connection point of the third switching means and the fourth switching means; And a second inductor magnetically coupled with the first inductor, connected between a first terminal of a primary winding of the transformer and a positive electrode of the input DC power supply. A first diode, a second diode connected between a second terminal of a primary winding of the transformer and a positive electrode of the input DC power supply, and a rectifier smoothing voltage induced in a secondary winding of the transformer. Rectifying and smoothing means, and On / off control means for controlling a duty ratio of a controllable switching element included in the second switching means, or a duty ratio of a controllable switching element included in the fourth switching means, or a ratio of both. A switching power supply device comprising: 4. The switching power supply according to claim 3, wherein each of the controllable switching elements included in the second switching means and the fourth switching means has a duty ratio of 50% or less. 5. The switching according to claim 1, wherein a phase of a pulse for turning on and off the first switching means and a phase of a pulse for turning on and off the third switching means are shifted by 180 °. Power supply. 6. The first switching means, the second switching means,
4. The switching device according to claim 1, wherein each of the switching device, the third switching device, and the fourth switching device includes a controllable switching element and a parallel-connected diode. Switching power supply. 7. The first switching means, the second switching means,
Each of the switching means, the third switching means and the fourth switching means are FETs which are controllable switching elements incorporating parallel diodes.
4. The method according to claim 1, wherein the first and second components are constituted by only the first and second components.
A switching power supply as described. 8. The first switching means, the second switching means,
Each of the switching means, the third switching means and the fourth switching means are constituted by a controllable switching element and a parallel connection of a diode, and the first switching means and the second switching means Each of the third switching means and the fourth switching means has control means for detecting an applied voltage and turning on the switching element when the detected applied voltage is substantially zero. The switching power supply device according to claim 1 or 3, wherein 9. The first switching means, the second switching means,
Each of the switching means, the third switching means and the fourth switching means are FETs which are controllable switching elements incorporating parallel diodes.
Each of the first switching means, the second switching means, the third switching means, and the fourth switching means detects an applied voltage, and the detected applied voltage is substantially 4. The switching power supply device according to claim 1, further comprising control means for turning on the switching element when the switching element is in a zero state. 10. The first switching means, the second switching means, the third switching means, and the fourth switching means, each comprising a controllable switching element and a parallel connection of a diode. Each of the first switching means, the second switching means, the third switching means, and the fourth switching means detects that a current flows through the diode included therein, and performs the switching. 4. The switching power supply according to claim 1, further comprising control means for turning on the element. 11. The FE, wherein each of the first switching means, the second switching means, the third switching means and the fourth switching means is a controllable switching element incorporating a parallel diode.
Each of the first switching unit, the second switching unit, the third switching unit, and the fourth switching unit detects that a current flows through the diode included in each of the first switching unit, the second switching unit, the third switching unit, and the fourth switching unit. 4. The switching power supply according to claim 1, further comprising control means for turning on the switching element. 12. A control device, comprising: a first switching element, a controllable switching element included in each of the first switching means, the second switching means, the third switching means, and the fourth switching means. A second switching element, a third switching element, and a fourth switching element; a period from when the first switching element shifts from on to off to when the second switching element shifts from off to on; And the period from when the second switching element transitions from on to off to when the first switching element transitions from off to on, and after the third switching element transitions from on to off. A period until the fourth switching element transitions from off to on, and 4. The switching power supply according to claim 1, further comprising control means for fixing a fixed period of time from when the third switching element changes from off to on to when the third switching element changes from on to off. .