JPH0686541A - Switching power supply - Google Patents

Abstract

(57) [Summary] [Objective] In a switching power supply device that supplies a stable DC voltage to various electronic devices, it is an object to solve the occurrence of switching loss and obtain high efficiency and low noise characteristics. [Structure] Input DC voltage source 1, first choke coil 3 and first switching element 1 connected in parallel therewith
A series circuit with the first choke coil 3, a series circuit with the capacitor 4 and the second switching element 14 connected in parallel with the first choke coil 3, and a second choke connected in parallel with the second switching element 14. Series circuit of coil 6 and output capacitor 7 and first and second switching elements 1
A configuration is provided in which a control circuit 15 that alternately drives 3 and 14 in a predetermined on / off period is provided. First switching element 1
By reverse-exciting the first choke coil 3 via the second switching element 14 during the OFF period of 3, the first and second switching elements 13 and 14 can achieve zero voltage turn-on, which is highly efficient and low. Noise characteristics can be obtained.

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 device for supplying a stable DC voltage to various electronic devices.

[0002]

2. Description of the Related Art In recent years, switching power supplies have been required to have high efficiency and low noise as electronic devices have become smaller and have higher functions.

A conventional switching power supply device will be described below. FIG. 9 shows a conventional switching power supply device, Z
FIG. 3 is a circuit configuration diagram of an input / output non-inverting buck-boost converter called an ETA converter. In FIG. 9, reference numeral 1 is an input DC voltage source, and its voltage is Ei. 2 is a switching element, 3 is a first choke coil, 4
Is a capacitor. The switching element 2 converts the input DC voltage Ei into a high frequency AC voltage and transmits it to the first choke coil 3 and the capacitor 4. The capacitance of the capacitor 4 is sufficiently large, and its voltage is regarded as the DC voltage Ec in the direction shown in FIG. 5 is a diode. Reference numeral 6 denotes a second choke coil, which can be magnetically coupled to the first choke coil 3 with the polarity shown in FIG. Reference numeral 7 is an output capacitor, and 8 is a load. The capacitance of the output capacitor 7 is sufficiently large, and the output DC voltage Eo is output to the load 8. Reference numeral 9 denotes a control circuit, which drives the switching element 2 in a predetermined on / off period to stabilize the output DC voltage Eo.

The operation of the switching power supply device configured as described above will be described below. First, when the switching element 2 is on, the voltage Ei is applied to the first choke coil 3 and the voltage Ei + Ec-Eo is applied to the second choke coil 6. A current that is the sum of the exciting currents of the first choke coil 3 and the second choke coil 6 flows through the switching element 2. Further, the exciting current of the second choke coil 6 flows through the capacitor 4. This period is Ton. Next, switching element 2
When is off, the voltage of each choke coil is inverted and the diode 5 becomes conductive. At this time, the voltage Ec is applied to the first choke coil 3 and the voltage Eo is applied to the second choke coil 6. A current that is the sum of the degaussing currents of the first choke coil 3 and the second choke coil 6 flows through the diode 5. The degaussing current of the first choke coil 3 flows through the capacitor 4. This period is Tof
f. In the stable operation state, the magnetic flux of each choke coil is reset in one cycle, so the following equation holds.

Ei · Ton = Ec · Toff (Ei + Ec−Eo) · Ton = Eo · Toff ∴ Eo = Ec = (Ton / Toff) · Ei That is, the output DC voltage Eo adjusts the on / off ratio of the switching element 2. By this, it is possible to stabilize.
FIG. 10 shows an operation waveform diagram of each part.

Further, since the voltages applied to the respective choke coils are equal, it can be seen that the first choke coil 3 and the second choke coil 6 can be magnetically coupled with the same number of turns. Although detailed description is omitted, this switching power supply device makes the current flowing in the second choke coil 6 an alternating current by making the winding ratio of the first choke coil 3 and the second choke coil 6 equal to its coupling coefficient. It has a feature that it can be a direct current having no component and that the ripple voltage superimposed on the output direct current voltage Eo can be 0V.

FIG. 11 shows a circuit diagram in which this switching power supply device is of an input / output insulation type. In FIG. 11, 10 is a transformer, 11 is its primary winding, and 12 is its secondary winding. The configuration is the same as the switching power supply device shown in FIG. 9 except that the transformer 10 is connected instead of the first choke coil 3 in FIG. The operation is similar to that of the switching power supply device of FIG. 9 except that the turns ratio is changed after the secondary winding 12.

However, a surge voltage due to the leakage inductance of the transformer 10 is generated during switching. Also in this switching power supply device, the transformer 10 and the choke coil 6 can be magnetically coupled, and by making the turns ratio of the secondary winding 12 and the choke coil 6 equal to the coupling coefficient,
The current flowing through the choke coil 6 is a direct current having no AC component, and the ripple voltage superimposed on the output DC voltage can be 0V. FIG. 12 shows the operation waveform chart of each part.

[0009]

However, in the above-mentioned conventional configuration, when the current flowing through the choke coil becomes 0 A when the load is light, the output DC voltage Eo is stabilized by T.
In order to make ON shorter, the inductance of the choke coil must be set large depending on the output specifications with a sudden change in load. When the switching element 2 is turned on, the diode 5 is conducting, so that a recovery current is generated. At this time, the voltage applied to the switching element 2 is rapidly discharged from Ei + Eo to 0 V, so that a turn-on loss occurs. . In addition to these, in the case of the insulation type as shown in FIG. 11, a large turn-off loss occurs due to the surge voltage due to the leakage inductance of the transformer 10 or a loss occurs in the snubber circuit, which lowers the efficiency. Had the problem.

The present invention solves the above-mentioned conventional problems, and provides a switching power supply device in which fluctuations in the on / off period of a switching element due to load conditions are suppressed, zero cross switching is realized to improve efficiency, and noise is reduced. The purpose is to

[0011]

In order to achieve this object, a switching power supply device of the present invention comprises an input DC voltage source, a first choke coil connected in parallel with the input DC voltage source, and a first choke coil. A series circuit with a switching element,
A series circuit including a second switching element and a capacitor connected in parallel with the first choke coil;
A series circuit of a second choke coil and an output capacitor connected in parallel with the switching element, and a control circuit for alternately turning on and off the first and second switching elements and adjusting their on / off periods to a predetermined value. Or a series circuit of an input DC voltage source, a primary winding of a transformer and a first switching element connected in parallel with the input DC voltage source, and a secondary winding of the transformer. A series circuit of a capacitor and a second switching element connected in parallel, a series circuit of a choke coil and an output capacitor connected in parallel with the second switching element, and the first and second switching elements And a configuration that includes a control circuit that alternately turns on and off and adjusts the on-off period to a predetermined value, or an input DC voltage source, and The are connected in parallel a series circuit of a primary winding of a transformer and a first switching element connected in parallel with the power DC voltage source, the primary winding of the transformer 1
A series circuit of a capacitor and a second switching element, a series circuit of a second capacitor and a diode connected in parallel with the secondary winding of the transformer, and a choke coil connected in parallel with the diode. It has a configuration including a series circuit with an output capacitor, and a control circuit that alternately turns on and off the first and second switching elements and adjusts their on / off periods to a predetermined value.

[0012]

With this configuration, the choke coil or the transformer can be reverse-excited via the second switching element during the off period of the first switching element. By using the reverse excitation energy, the first and second switching elements can be turned on at zero voltage. Further, since the current of the choke coil always flows linearly and continuously, there is no so-called discontinuous operation, and variation in the on / off period of the switching element due to load conditions can be suppressed.

[0013]

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the first of the present invention.
6 is a circuit configuration diagram of the switching power supply device in the embodiment of FIG. In FIG. 1, 1 is an input DC voltage source, and its voltage is Ei. Reference numeral 13 is a first switching element, which is composed of a parallel circuit of a diode and a switch, such as a MOSFET. 3 is a first choke coil, and 4 is a capacitor. The first switching element 13 converts the input voltage Ei into a high frequency AC voltage and transmits it to the first choke coil 3 and the capacitor 4. The capacitance of the capacitor 4 is sufficiently large, and its voltage is regarded as the DC voltage Ec in the direction shown in FIG. A second switching element 14 is composed of a parallel circuit of a diode and a switch, such as a MOSFET.
Reference numeral 6 is a second choke coil, which can be magnetically coupled to the first choke coil 3 with the polarity shown in FIG. Reference numeral 7 is an output capacitor, and 8 is a load. The capacitance of the output capacitor 7 is sufficiently large, and the output DC voltage Eo is output to the load 8. Reference numeral 15 is a control circuit, which alternately drives the first switching element 13 and the second switching element 14 in a predetermined on / off period in order to stabilize the output DC voltage Eo.

The operation of the switching power supply device configured as described above will be described with reference to the operation waveform chart of each part shown in FIG. First, when the first switching element 13 is on, the input voltage Ei is applied to the first choke coil 3 and the voltage Ei + Ec-Eo is applied to the second choke coil 6. A current that is the sum of the exciting currents of the first choke coil 3 and the second choke coil 6 flows through the first switching element 13. Further, the exciting current of the second choke coil 6 flows through the capacitor 4.
This period is Ton.

Next, when the first switching element 13 is off, the voltage of each choke coil is inverted and the second switching element 14 is turned on. At this time, the voltage Ec is applied to the first choke coil 3 and the voltage Eo is applied to the second choke coil 6. A current that is the sum of the degaussing currents of the first choke coil 3 and the second choke coil 6 flows through the second switching element 14. The degaussing current of the first choke coil 3 flows through the capacitor 4. This period is Toff. In the stable operation state, the magnetic flux of each choke coil is reset in one cycle, so that the following equation holds true as in the conventional example shown in FIG.

∴ Eo = Ec = (Ton / Toff) · Ei That is, the output DC voltage Eo is the first switching element 13
It can be stabilized by adjusting the on / off period of the second switching element 14.

The switching power supply according to this embodiment differs from the conventional switching power supply shown in FIG.
This means that the first choke coil 3 or the second choke coil 6 is reversely excited by the second switching element 14. For this reason, since the current of the choke coil always flows linearly and continuously, there is no so-called discontinuous operation, fluctuations in the on / off period of the switching element due to load conditions are suppressed, and their inductances can be set smaller than before. . In addition, the second switching element 1
At the time of turn-off of No. 4, by the reverse excitation energy, the first
The charge accumulated in the parasitic capacitance of the switching element 13 or the electrostatic capacitance element connected to reduce the turn-off loss is regenerated to the input DC voltage source 1 through the first choke coil 3 and does not cause the turn-on loss.

Similarly, when the first switching element 13 is turned off, the charge accumulated in the parasitic capacitance of the second switching element 14 or the electrostatic capacitance element connected to reduce the turn-off loss is reduced by the excitation energy due to the excitation energy. Since it is discharged to the output capacitor 7 via the choke coil 6 of the above, there is no turn-on loss. That is, the excellent effect that the first switching element 13 and the second switching element 14 are both turned on at zero voltage is obtained.

Further, according to the present embodiment, the first choke coil 3 and the second choke coil 6 can be magnetically coupled with the same number of turns, and the first choke coil 3 and the second choke coil 6 are connected. By making the turns ratio equal to its coupling coefficient, the current flowing through the second choke coil 6 can be made a direct current having no AC component, and the ripple voltage superimposed on the output DC voltage Eo can be made 0V. It does not impair the characteristic of the ZETA converter.

As described above, according to this embodiment, the conventional Z
By using the diode of the ETA converter as the second switching element, if the saturation voltage is smaller than the forward voltage of the diode, the loss is reduced, the recovery current is also eliminated, and the fluctuation of the ON / OFF period of the switching element due to the load condition is reduced. By suppressing and realizing zero-cross switching, efficiency can be improved and noise can be reduced.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to the drawings. In FIG. 3, 1
Is an input DC voltage source, and its voltage is Ei. Thirteen
Is a first switching element, 10 is a transformer, 11 is its primary winding, and 12 is a secondary winding. 16
Is a resonance capacitor, and equivalently includes a parasitic capacitance connected in parallel with the first switching element 13. Reference numeral 4 is a capacitor. The first switching element 13 has an input voltage E
i is converted into a high frequency AC voltage and applied to the primary winding 11,
It is transmitted to the secondary winding 12. The capacitance of the capacitor 4 is sufficiently large, and its voltage is a DC voltage Ec in the direction shown in FIG.
To consider. 14 is a second switching element. Reference numeral 6 is a choke coil, which can be magnetically coupled to the transformer 10 with the polarity shown in FIG. Reference numeral 7 is an output capacitor, and 8 is a load. The capacitance of the output capacitor 7 is sufficiently large, and the output DC voltage Eo is output to the load 8.
Reference numeral 15 is a control circuit, which alternately drives the switching elements 13 and 14 in a predetermined on / off period in order to stabilize the output DC voltage Eo.

The switching power supply device configured as described above is an insulating type in which the first choke coil 3 of the switching power supply device of FIG. 1 shown in the first embodiment is replaced with a transformer 10. The operation is similar to that of the switching power supply device of FIG. 1, except that the turns ratio is converted after the secondary winding 12. The turn ratio of the transformer 10 is n. First, when the first switching element 13 is on, the voltage Ei is applied to the primary winding 11 and the secondary winding 12
A voltage Ei / n is induced in the coil, and a voltage Ei / n + Ec-Eo is applied to the choke coil 6. This period is To
n. Next, when the first switching element 13 is off, the voltages of the transformer 10 and the choke coil 6 are inverted,
The second switching element 14 is turned on. At this time, the voltage n · Ec is applied to the primary winding 11 and the voltage Eo is applied to the choke coil 6. This period is To
ff. In the stable operation state, the magnetic flux of the transformer 10 and the choke coil 6 is reset in one cycle,
The following equation holds.

∴ Eo = Ec = (Ton / Toff) · Ei / n That is, the output DC voltage Eo is the first switching element 13
It can be stabilized by adjusting the on / off period of the second switching element 14. FIG. 4 shows an operation waveform diagram of each part of the switching power supply device according to the present embodiment.

The switching power supply device according to this embodiment is different from the conventional switching power supply device shown in FIG.
Alternatively, the choke coil 6 is reversely excited. Therefore, since the current of the choke coil 6 always flows linearly and continuously, there is no so-called discontinuous operation, fluctuations in the on / off period of the switching element due to load conditions are suppressed, and the inductances thereof are set smaller than in the past. it can. Further, when the second switching element 14 is turned off, the charge stored in the resonance capacitor 16 which is a capacitive element connected to reduce parasitic capacitance or turn-off loss of the first switching element 13 by the reverse excitation energy is generated. Input DC voltage source 1 via primary winding 11
It is regenerated into a turn-on loss.

Similarly, when the first switching element 13 is turned off, the charge stored in the parasitic capacitance of the second switching element 14 or the electrostatic capacitance element connected to reduce the turn-off loss due to the excitation energy is choke coil. Since it is discharged to the output capacitor 7 via 6, there is no turn-on loss. That is, the excellent effect that the first switching element 13 and the second switching element 14 are both turned on at zero voltage is obtained.

In addition, according to the present embodiment, the transformer 10-2
The secondary winding 12 and the choke coil 6 can be magnetically coupled with the same number of turns, and the winding ratio of the secondary winding 12 and the choke coil 6 is made equal to the coupling coefficient, so that the current flowing through the choke coil 6 is increased. Can be a direct current having no AC component, and the characteristic of the ZETA converter that the ripple voltage superimposed on the output DC voltage Eo can be 0 V is not impaired.

As described above, according to this embodiment, the diode of the conventional insulated type ZETA converter is used as the second switching element, so that the loss is reduced if the saturation voltage is smaller than the forward voltage of the diode. Also, the recovery current is eliminated, fluctuation of the on / off period of the switching element due to the load condition is suppressed, and the efficiency can be improved and the noise can be reduced by realizing the zero-cross switching.

(Embodiment 3) A third embodiment of the present invention will be described below with reference to the drawings. In FIG. 5, 1
Is an input DC voltage source, and its voltage is Ei. Thirteen
Is a first switching element, 10 is a transformer, 11 is its primary winding, and 12 is a secondary winding. First
The switching element 13 converts the input voltage Ei into a high frequency AC voltage, applies it to the primary winding 11, and transmits it to the secondary winding 12. Reference numeral 14 is a second switching element, 17 is a first capacitor, and the second switching element 14 and the first
The series circuit of the capacitor 17 is connected to the primary winding 11 in parallel. The capacitance of the first capacitor 17 is sufficiently large, and its voltage is regarded as the DC voltage E17 in the direction shown in FIG. Reference numeral 16 is a resonance capacitor, which includes a parasitic capacitance equivalently connected in parallel with the first switching element 13.
Reference numeral 4 is a second capacitor. The capacitance of the second capacitor 4 is sufficiently large, and its voltage is regarded as the DC voltage Ec in the direction shown in FIG. Reference numeral 6 is a choke coil, which can be magnetically coupled to the transformer 10 with the polarity shown in FIG.
Reference numeral 7 is an output capacitor, and 8 is a load. The capacitance of the output capacitor 7 is sufficiently large, and the output DC voltage Eo is output to the load 8. Reference numeral 15 is a control circuit, which alternately drives the switching elements 13 and 14 in a predetermined on / off period in order to stabilize the output DC voltage Eo.

The operation of the switching power supply device configured as described above will be described with reference to the operation waveform chart of each part shown in FIG. The turn ratio of the transformer 10 is n. First, when the first switching element 13 is on, the input voltage Ei is applied to the primary winding 11 and the voltage Ei / n + Ec-Eo is applied to the choke coil 6.
A current that is the sum of the exciting currents of the primary winding 11 and the choke coil 6 flows through the first switching element 13. The second
The exciting current of the choke coil 6 flows through the capacitor 4. This period is Ton.

Next, when the first switching element 13 is off, the voltage of the winding of the transformer 10 and the voltage of the choke coil 6 are inverted, the second switching element 14 is turned on, and the diode 5 is turned on. At this time, the voltage E17 is applied to the primary winding 11.
(= N · Ec) is applied and the voltage Eo is applied to the choke coil 6. In the second switching element 14, a current that linearly decreases with the primary winding current that was flowing when the first switching element 13 was turned off as an initial value flows. In the stable operation state, the charging / discharging current of the first capacitor 17 is equal. In the second capacitor 4, the degaussing current of the primary winding 11 and the second switching element 1
A current that is n times the difference between the currents flowing in 4 flows. A difference between the current flowing through the second capacitor 4 and the degaussing current of the choke coil 6 flows through the diode 5. This period is Toff. In the stable operation state, the magnetic fluxes of the transformer 10 and the choke coil 6 are reset in one cycle, so that the following equation holds true as in the second embodiment shown in FIG.

∴ Eo = Ec = (Ton / Toff) · Ei / n That is, the output DC voltage Eo is the first switching element 13
It can be stabilized by adjusting the on / off period of the second switching element 14.

The switching power supply device according to this embodiment is different from the switching power supply device according to the second embodiment shown in FIG. 3 in that the reverse excitation of the transformer 10 is different from that of the second switching element 14 installed on the primary side. This is done by the first capacitor 17. Therefore, the choke coil 6
Although the current discontinuous operation of 7 is inevitable, a strong voltage clamping function is obtained by the second switching element 14 and the first capacitor 17, and the surge voltage is not generated. Further, when the second switching element 14 is turned off, the charge stored in the resonance capacitor 16 which is a capacitive element connected to reduce parasitic capacitance or turn-off loss of the first switching element 13 by the reverse excitation energy is generated. It is regenerated to the input DC voltage source 1 via the primary winding 11 and does not cause a turn-on loss.

Similarly, when the first switching element 13 is turned off, the charge stored in the parasitic capacitance of the second switching element 14 or the electrostatic capacitance element connected to reduce the turn-off loss due to the excitation energy is choke coil. Since it is discharged to the output capacitor 7 via 6, there is no turn-on loss. That is, the excellent effect that the first switching element 13 and the second switching element 14 are both turned on at zero voltage is obtained.

According to the present embodiment, the secondary winding 12 of the transformer 10 and the choke coil 6 can be magnetically coupled with the same number of turns, and the secondary winding 12 and the choke coil 6 can be coupled.
By equalizing the turns ratio with the coupling coefficient thereof, the current flowing through the choke coil 6 can be made a direct current having no AC component, and the ripple voltage superimposed on the output DC voltage can be made 0V. It does not impair the characteristics of the ZETA converter. In this case, the choke current discontinuous operation described above can be avoided, and fluctuations in the on / off period of the switching element at a light load can be suppressed.

As described above, according to this embodiment, the primary winding 11 of the transformer 10 of the conventional insulation type ZETA converter is used.
By providing a series circuit of the capacitor 17 and the second switching element 14 in the zero crossing switching of each switching element can be achieved, the surge voltage is eliminated by the strong clamp function, and high efficiency and low noise can be achieved. Can be achieved.

(Embodiment 4) A fourth embodiment of the present invention will be described below with reference to the drawings. In FIG. 7, 1
Is an input DC voltage source, and its voltage is Ei. Thirteen
Is a first switching element, 10 is a transformer, 11 is its primary winding, and 12 is a secondary winding. First
The switching element 13 converts the input voltage Ei into a high frequency AC voltage, applies it to the primary winding 11, and transmits it to the secondary winding 12. Reference numeral 14 is a second switching element, 17 is a first capacitor, and the second switching element 14 and the first
The series circuit of the capacitor 17 is connected to the primary winding 11 in parallel. The voltage of the first capacitor 17 is E17 in the direction shown in FIG. Reference numeral 16 is a resonance capacitor, which includes a parasitic capacitance equivalently connected in parallel with the first switching element 13. 18 is an inductor, transformer 1
Including the leakage inductance of 0, the second switching element 14, the first capacitor 17, and the primary winding 11 are equivalently included.
Connected in a loop. Reference numeral 4 is a second capacitor. The capacitance of the second capacitor 4 is sufficiently large, and its voltage is regarded as the DC voltage Ec in the direction shown in FIG. Reference numeral 6 is a choke coil, which can be magnetically coupled to the transformer 10 with the polarity shown in FIG. Reference numeral 7 is an output capacitor, and 8 is a load. The capacitance of the output capacitor 7 is sufficiently large, and the output DC voltage Eo is output to the load 8.
Reference numeral 15 denotes a control circuit, which alternately drives the switching elements 13 and 14 in a predetermined on / off period in order to stabilize the output DC voltage Eo.

The operation of the switching power supply device configured as described above will be described with reference to the operation waveform chart of each part shown in FIG. The turn ratio of the transformer 10 is n. First, when the first switching element 13 is on, the input voltage Ei is applied to the primary winding 11 and the voltage Ei / n + Ec-Eo is applied to the choke coil 6.
A current that is the sum of the exciting currents of the primary winding 11 and the choke coil 6 flows through the first switching element 13. The second
The exciting current of the choke coil 6 flows through the capacitor 4. This period is Ton.

Next, when the first switching element 13 is turned off, the voltage of the winding of the transformer 10 and the voltage of the choke coil 6 are inverted (Tf in FIG. 8), and the second switching element 1
4 turns on. At this time (T1 in FIG. 8), E17 is applied to the primary winding 11 and approximately voltage Eo is applied to the choke coil 6. In the second switching element 14, a current that linearly decreases with the primary winding current that was flowing when the first switching element 13 was turned off as an initial value flows. The primary winding 11 is attached to the second capacitor 4.
Current and the degaussing current of the choke coil 6 which is n times the difference between the degaussing current and the current flowing through the second switching element 14. The first capacitor 17 is charged and E17 = n ·
When it becomes Ec, the diode 5 becomes conductive. At this time (Fig. 8
In T2), the resonance current of the first capacitor 17 and the inductor 18 flows through each part. When the current flowing through the diode 5 becomes 0 A and turns off, the state returns to the same state as T1 (T3 in FIG. 8), and eventually the second switching element 14
Turns off. In the stable operation state, the charge and discharge currents of the first capacitor 17 are equal. The above period is Toff. In the stable operation state, the magnetic fluxes of the transformer 10 and the choke coil 6 are reset in one cycle, so that the following equation holds true as in the second embodiment shown in FIG.

∴ Eo = Ec = (Ton / Toff) · Ei / n That is, the output DC voltage Eo is equal to the first switching element 13
It can be stabilized by adjusting the on / off period of the second switching element 14.

The switching power supply device according to this embodiment is different from the switching power supply device according to the third embodiment shown in FIG. 5 in that the current flowing through the diode 5 is a resonance current, so that the diode 5 can be turned off at zero current. is there. Therefore, the recovery current of the diode 5 is not generated, and in addition to the effect of the third embodiment, the effect of further reducing the noise can be obtained.

In addition, according to the present embodiment, the transformer 10-2 is used.
The secondary winding 12 and the choke coil 6 can be magnetically coupled with the same number of turns, and the winding ratio of the secondary winding 12 and the choke coil 6 is made equal to the coupling coefficient, so that the current flowing through the choke coil 6 is increased. Can be a direct current having no AC component, and the characteristic of the ZETA converter that the ripple voltage superimposed on the output DC voltage can be 0 V is not impaired.

As described above, according to the present embodiment, the series circuit of the capacitor and the second switching element is provided in the primary winding of the transformer of the conventional insulated type ZETA converter, and whether the leakage inductance of the transformer is used or not. Alternatively, by connecting an inductor, the zero-cross switching of each switching element can be achieved, and the strong clamping function eliminates the generation of surge voltage, thereby achieving high efficiency and low noise. In addition to this, the effect of eliminating the recovery current of the diode by current resonance and further reducing the noise can be obtained.

[0043]

As described above, according to the present invention, an input DC voltage source, a series circuit of a first choke coil and a first switching element connected in parallel with the input DC voltage source,
A series circuit including a second switching element and a capacitor connected in parallel with the first choke coil;
A series circuit of a second choke coil and an output capacitor connected in parallel with the switching element, and a control circuit for alternately turning on and off the first and second switching elements and adjusting their on / off periods to a predetermined value. With the configuration including and, the choke coil is reverse-excited through the second switching element during the off period of the first switching element, and the reverse excitation energy is used to generate the first and second The switching element can be turned on at zero voltage. In addition, since the current of the choke coil always flows linearly and continuously, there is no so-called discontinuous operation, fluctuation of the on / off period of the switching element due to load conditions is suppressed, and diode recovery current is also eliminated, resulting in high efficiency and low operation. It is possible to realize an excellent switching power supply device with no noise.

In addition, an input DC voltage source, a series circuit of a primary winding of a transformer and a first switching element connected in parallel with the input DC voltage source, and a secondary winding of the transformer in parallel. A series circuit of a connected capacitor and a second switching element, a series circuit of a choke coil and an output capacitor connected in parallel with the second switching element, and the first and second switching elements are alternated. By having a configuration that includes a control circuit that turns on and off and adjusts those on and off periods to a predetermined value, the transformer is reversely excited via the second switching element during the off period of the first switching element, By utilizing the reverse excitation energy, the first and second switching elements can be turned on at zero voltage. In addition, since the current of the choke coil always flows linearly continuously, there is no so-called discontinuous operation, fluctuation of the on / off period of the switching element due to load conditions is suppressed, diode recovery current is also eliminated, and high efficiency is achieved. It is possible to realize an excellent insulated switching power supply device with low noise.

In addition, an input DC voltage source, a series circuit of a primary winding of a transformer and a first switching element, which are continuous in parallel with the input DC voltage source, and a primary winding of the transformer are connected in parallel. A series circuit of a first capacitor and a second switching element connected, a series circuit of a second capacitor and a diode connected in parallel with the secondary winding of the transformer, and a parallel circuit of the diode And a control circuit that alternately turns on and off the first and second switching elements and adjusts their on / off period to a predetermined value. The transformer can be reverse-excited through the second switching element and the second capacitor during the off period of the first switching element.
By using the reverse excitation energy, the first and second
The switching element can be turned on at zero voltage, and the strong clamping function of the second switching element and the second capacitor can eliminate the surge voltage. Further, since the current of the choke coil always flows continuously linearly, it is possible to realize an excellent insulated switching power supply device with high efficiency and low noise.
Further, current resonance between the second capacitor and the leakage inductance of the transformer or an inductor connected separately makes it possible to achieve further noise reduction without diode recovery current.

[Brief description of drawings]

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

FIG. 2 is an operation waveform diagram of each part of the switching power supply device according to the first embodiment.

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

FIG. 4 is an operation waveform diagram of each part of the switching power supply device according to the second embodiment.

FIG. 5 is a circuit configuration diagram of a switching power supply device according to a third embodiment of the present invention.

FIG. 6 is an operation waveform diagram of each part of the switching power supply device according to the third embodiment.

FIG. 7 is a circuit configuration diagram of a switching power supply device according to a fourth embodiment of the present invention.

FIG. 8 is an operation waveform diagram of each part of the switching power supply device according to the fourth embodiment.

FIG. 9 is a circuit configuration diagram of a conventional switching power supply device.

FIG. 10 is an operation waveform diagram of each part of the conventional switching power supply device.

FIG. 11 is a circuit configuration diagram of a conventional switching power supply device.

FIG. 12 is an operation waveform diagram of each part of the conventional switching power supply device.

[Explanation of symbols]

 1 Input DC Voltage Source 3 First Choke Coil 4 Capacitor 5 Diode 6 Second Choke Coil 7 Output Capacitor 8 Load 10 Transformer 11 Primary Winding 12 Secondary Winding 13 First Switching Element 14 Second Switching Element 15 Control Circuit 16 Resonant Capacitor 17 First Capacitor 18 Inductor

(72) Inventor Takaharu Murakami 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Toshinari Ueyama, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (7)

[Claims] 1. A series circuit of an input DC voltage source, a first choke coil and a first switching element connected in parallel with the input DC voltage source, and a series circuit connected in parallel with the first choke coil. A series circuit of a capacitor and a second switching element, a series circuit of a second choke coil and an output capacitor connected in parallel with the second switching element, and the first and second switching elements. A switching power supply device comprising: a control circuit that alternately turns on and off and adjusts the on and off periods to a predetermined value, and supplies the voltage of the output capacitor as an output DC voltage to a load. 2. The switching power supply device according to claim 1, wherein the first and second choke coils are magnetically coupled. 3. A transformer having an input DC voltage source, at least a primary winding and a secondary winding, a primary winding of the transformer connected in parallel with the input DC voltage source, and a first switching element. , A series circuit of a capacitor connected in parallel with the secondary winding of the transformer and a second switching element, a choke coil connected in parallel with the second switching element, and an output capacitor. And a control circuit that alternately turns on and off the first and second switching elements and adjusts their on / off period to a predetermined value, and supplies the voltage of the output capacitor as an output DC voltage to a load. Switching power supply. 4. The switching power supply device according to claim 3, wherein the transformer and the choke coil are magnetically coupled. 5. A transformer having an input DC voltage source, at least a primary winding and a secondary winding, a primary winding of the transformer connected in parallel with the input DC voltage source, and a first switching element. , A series circuit of a first capacitor and a second switching element connected in parallel with the primary winding of the transformer, and a second circuit connected in parallel with the secondary winding of the transformer. , A series circuit of a capacitor and a diode, a series circuit of a choke coil connected in parallel with the diode and an output capacitor, and the first and second
And a control circuit for alternately turning on and off the switching elements and adjusting their on / off periods to a predetermined value, and supplying the voltage of the output capacitor as an output DC voltage to a load. 6. The switching power supply device according to claim 5, wherein the transformer and the choke coil are magnetically coupled. 7. When the second switching element is on, the leakage inductance of the transformer or the inductance connected in series with the primary winding of the transformer causes the first capacitor to resonate, and the secondary winding current is the resonance current. The switching power supply device according to claim 5, which is configured as follows.