JP2001211666A - Switching power supply circuit - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To suppress generation of steep charge / discharge current when turning on a MOS switch, and to reduce noise and switching loss. A current flows in a saturable reactor (22, 23) in a direction of an arrow (A) from time T0 to T1, and electric energy is stored in an auxiliary coil (24). Further, electric charges are accumulated in the MOS switches 27 and 28. When the current flowing through the saturable reactors 22 and 23 stops at the time T1, the electric energy tends to move in the direction of arrow B, so that the saturable reactor 2 having the magnetic hysteresis characteristic is used.
2 and 23 exhibit a high impedance state 1. The electric energy stored in the auxiliary coil 24 is transferred to the MOS switch 25
Then, the electric charges accumulated in the MOS switches 27 and 28 are discharged, and the electric charges are charged in the MOS switches 25 and 26.

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.

[0002]

2. Description of the Related Art FIG. 7A shows a general full-bridge type switching power supply circuit. In this configuration, a current is supplied to the transformer 71 through the switch elements 72 to 75, which are MOS-FETs, and a load is output by the action of electromagnetic induction of the transformer 71. Here, each of the switch elements 72 to 7
A control voltage of 5 is applied as shown in FIG. 7B. FIG. 8 shows a voltage waveform at point A in FIG. 7A.

In the time T0 to T1, since the MOS-FET has a parasitic capacitance, charges are accumulated in the switching elements 74 and 75. And after the dead time has passed (time T2)
In this case, the charge remains (see FIG. 8), and when the switch elements 74 and 75 are turned ON in that state, a steep charge / discharge current is generated, which causes noise and switching loss.

FIG. 9 shows a switching power supply circuit provided with an auxiliary coil 76 in series with a transformer 71 in order to discharge the electric charges stored in the switch elements 74 and 75. FIG. 10 shows the voltage waveform at point A in FIG.

At time T0 to T1, switching element 7
Electric charges are stored in the auxiliary coils 4 and 75, and electric energy is stored in the auxiliary coil 76. Then, in the dead time (time T1 to T2), the electric energy stored in the auxiliary coil 76 moves to the switching elements 74 and 75, and discharges the electric charges stored in the switching elements 74 and 75, and also discharges the switching elements 72 and 75. 73 is charged with electric charge. Therefore, at the time of heavy load, the voltage applied to the switch elements 74 and 75 can be shifted to zero or a low level within the dead time (see FIG. 10).

[0006]

However, the switching power supply as described above has the following problems.

As shown in FIG. 10, when the load is light, sufficient electric energy is not stored in the auxiliary coil 76, and the charges stored in the switching elements 74 and 75 cannot be completely discharged. When the switch elements 74 and 75 are turned on in a state where the electric charge is accumulated, a steep charge / discharge current is generated, and noise and switching loss occur.

Also, the input voltage is divided by the auxiliary coil 76 and the primary coil of the transformer 71, and as the load becomes heavier, the voltage on the transformer 71 decreases, and the output impedance increases.

[0009]

Means for Solving the Problems and Effects of the Invention
The switching power supply circuit includes a primary coil and a secondary coil that are opposed to each other, and a load output unit that outputs a load from the secondary coil by an action of electromagnetic induction generated by a current flowing through the primary coil, and a parasitic capacitance. A switch unit for determining an energized state and a non-energized state of the primary coil, and a low impedance state between the switch unit and the primary coil in the energized state, and changing the energized state to the non-energized state. A variable impedance means for setting a high impedance state between the switch unit and the primary coil at the time of transition; an energy storage unit capable of storing electric energy between the variable impedance means and the switch unit; The height of the variable impedance means when shifting from the energized state to the non-energized state The impedance state, the electric energy the stored in the energy storage unit in the energizing state is suppressed from moving to the load output portion,
In the power supply state, the electric energy stored in the energy storage unit moves to the switch unit, so that the electric charge stored in the parasitic capacitance in the switch unit in the power supply state is discharged.

Therefore, even at a light load, the switch section can be switched from the cut-off state to the continuous state in a state where no electric charge is stored, so that generation of a steep charge / discharge current is suppressed, noise is reduced, and switching is performed. Loss can be reduced.

The switching power supply circuit according to a third aspect of the present invention is characterized in that the energy storage section is provided in parallel with the primary coil and the variable impedance means.

Therefore, since the voltage applied to the primary coil is not affected by the energy storage section, the insertion of the energy storage section does not increase the output impedance.

According to a fourth aspect of the present invention, in the switching power supply circuit, the switch section includes first, second, third, and fourth switch elements, and the first and second switch elements are in a connected state. And when the fourth switch element is in a disconnected state, a first current is supplied to the primary coil, the energy storage section, and the variable impedance means,
And the fourth switch element are in the connected state, and the first and the second
When the switch element is in a disconnected state, a current is supplied to the primary coil, the energy storage unit and the variable impedance means in a direction opposite to the first current,
When the first, second, third and fourth switch elements are in a disconnected state, no current is supplied to the primary coil, the energy storage section and the variable impedance means.

Therefore, it is possible to suppress the generation of a steep charge / discharge current when the state of the switch section is shifted, to reduce noise and switching loss, and to obtain a stable load from the secondary coil.

According to a sixth aspect of the present invention, in the switching power supply circuit, the switch section includes a fifth switch element and a sixth switch element, wherein the fifth switch element is in a connected state and the sixth switch element is in a disconnected state. At the time, when the second current is supplied to the primary coil, the energy storage unit, and the variable impedance means, the fifth switch element is turned off, and the sixth switch element is turned on, Said 1
A current is supplied to the next coil, the energy storage unit, and the variable impedance means in a direction opposite to the second current, and when the fifth and sixth switch elements are in a disconnected state,
A current is not supplied to the primary coil, the energy storage unit, and the variable impedance means.

Therefore, the generation of a steep charge / discharge current when the state of the switch section is shifted is suppressed with a compact configuration,
Noise can be reduced.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As a preferred embodiment of the present invention, a full bridge type and a half bridge type will be described below.

FIG. 1 shows a functional block diagram of the first embodiment.

When the variable impedance means 12 and 13 are in a low impedance state in the energized state due to the connection state of the switch sections 15 and 16 and the cutoff state of the switch sections 17 and 18, current flows through the load output section 11 and electromagnetic induction occurs. The load is output by the action of. At the same time, electric energy is stored in the energy storage unit 14. Further, since the switches 17 and 18 have a parasitic capacitance, charges are accumulated.

Next, when the switches 15 and 16 are turned off to shift from the energized state to the non-energized state, the variable impedance means 12 and 13 exhibit a high impedance state, and the electric energy stored in the energy storage section 14 is stored. To the load output unit 11. Therefore, the electric energy moves to the switch units 17 and 18, and the electric charges accumulated in the switch units 17 and 18 are discharged.

2. First Embodiment 2.1 Overall Configuration FIG. 2A shows the overall configuration of a full-bridge switching power supply circuit. This is to output a load from the secondary coil 32 by the action of electromagnetic induction between the primary coil 31 and the secondary coil 32 of the transformer 21 which is a load output unit.

At both ends of the primary coil 31, a saturable reactor 22 as first variable impedance means and a saturable reactor 23 as second variable impedance means having a common core are provided. Further, an auxiliary coil 24 as an energy storage unit is provided in parallel with the primary coil 31 and the saturable reactors 22 and 23. Also, a switch unit is provided in series with the primary coil 31 and the like.
MOS switches 25 to 28 are provided, and a controller 33 as a first control device for operating the MOS switches is provided. Further, a rectifying circuit 34 for rectifying the AC current, and a smoothing capacitor 3 for smoothing the current passing through the rectifying circuit 34.
5 is provided.

Here, the first switch element is a MOS switch 25, the second switch element is a MOS switch 26,
Is a MOS switch 27, and the fourth switch element is a MOS switch 28.

It is not necessary to share the core of the saturable reactor 22 and that of the saturable reactor 23, and they may be separate. The saturable reactor is 2
It is not necessary to use one, and one saturable reactor may be provided in series at one end of the primary coil 31.

Next, the saturable reactors 22 and 23 will be described below. FIG. 3 shows the magnetic hysteresis characteristics of the magnetic field H and the magnetic flux density B when an amorphous core is used. Here, since there is a relationship between the slope of the curve and the magnitude of the impedance, high impedance states 1 and 2 and low impedance states 1 and 2 are exhibited at each position on the curve.

When a current is applied in the direction of arrow A in FIG. 2A, a low impedance state 1 is exhibited. When the current is stopped, when a current is applied in the direction of arrow B, the polarity is inverted. 1 and low impedance state 2 is exhibited. Next, in this state, even if a current flows in the direction of arrow B in FIG. 2A, the state remains in the low impedance state 2. After the state 2, the state becomes the saturation state 2 and the low impedance state 1 is exhibited.

Therefore, in the energized state, a low impedance state is exhibited. When the current is stopped and a current is caused to flow in a direction opposite to the current, a high impedance state is exhibited.

Incidentally, the saturable reactors 22 and 2 are set so as to quickly shift from the high impedance state to the saturated state.
3. Select 3 cores and number of turns.

The core of the saturable reactor is not limited to amorphous.

2.2 Operation The operation of the above switching power supply circuit will be described below.

A control voltage for each MOS switch is applied as shown in FIG. 2B. The voltage waveform at point A and the voltage waveform at point B in FIG. 2A in this case are shown in FIGS. Below, time T
The description will be given according to the progress of 0 to T4.

At time T0 to T1, a first current, which is a current in a direction indicated by an arrow A in FIG. 2A, flows through the saturable reactors 22 and 23. Therefore, the saturable reactors 22 and 23
Presents a low impedance state 1 in FIG. 2 and a current flows in the direction of arrow C in FIG.
The load is output from the secondary coil 32 due to the action of the electromagnetic induction between them. Further, since current also flows through the auxiliary coil 24, electric energy is stored.

As shown in FIG. 4, time T0 to T1
, The electric charge is accumulated in the MOS switch 28. This is because the MOS-FET used for the MOS switch has a parasitic capacitance. Note that the MOS switch 27 similarly stores charge.

At time T1, when the current in the direction of arrow A stops, the electric energy stored in the auxiliary coil 24 tends to move in the direction of arrow B with respect to the saturable reactors 22 and 23. At this time, the saturable reactor 22,
In the high impedance state 23 shown in FIG.
Therefore, the transfer of the electric energy stored in the auxiliary coil 24 to the primary coil 31 is prevented. Therefore, the electric energy moves in the direction of each of the MOS switches 25 to 28, so that at time T0 to T1, the MOS switch 2
The electric charges accumulated in 7 and 28 are discharged, and the potential at point A in FIG. 2A becomes about 0 (v) as shown in FIG. At time T2, the MOS switch 2
7, 28 can be turned ON.

In the time T1 to T2, the MOS switches 25 and 26 are charged.

At time T2, the saturable reactor does not reach the saturation state 1 shown in FIG.
(Dead time).

During the time T2 to T3, the saturable reactors 22 and 23 are in the low impedance state 2 shown in FIG. 3, so that a current flows in the direction of arrow D in FIG. The effect of electromagnetic induction between
The load is output from the secondary coil 32. Further, since current also flows through the auxiliary coil 24, electric energy is stored.

Further, as shown in FIG.
, The electric charge is accumulated in the MOS switch 26. Similarly, electric charge is accumulated in the MOS switch 25.

When the current in the direction of arrow B stops at time T3, the electric energy stored in the auxiliary coil 24 tends to move in the direction of arrow A with respect to the saturable reactors 22 and 23. At this time, the saturable reactor 22,
In the high impedance state 23 shown in FIG.
Therefore, the transfer of the electric energy stored in the auxiliary coil 24 to the primary coil 31 is prevented. Therefore, the electric energy moves in the direction of each of the MOS switches 25 to 28, so that the MOS switch 2
The electric charges stored in 5, 26 are discharged, and the potential at point B in FIG. 2A becomes about 0 (v) as shown in FIG. At time T4, when the electric charge is not charged, the MOS switch 2
5, 26 can be turned ON.

In the period between T3 and T4, the MOS switches 27 and 28 are charged.

At the time T4, the saturable reactor does not reach the saturated state 2 in FIG.
(Dead time).

Therefore, even under a light load, the MOS switch can be turned on in a state where no electric charge is stored,
The generation of steep charge / discharge current can be suppressed, and noise and switching loss can be reduced.

3. Second Embodiment 3.1 Overall Configuration FIG. 6A shows an overall configuration of a half-bridge type switching power supply circuit. This is because the load 41 is a transformer 41
The load is output from the secondary coil 52 by the action of electromagnetic induction between the primary coil 51 and the secondary coil 52.

A saturable reactor 42 as variable impedance means is provided at both ends of the primary coil 51 in series. In addition, in parallel with the primary coil 51 and the saturable reactor 42, an auxiliary coil 43 serving as an energy storage unit is provided.
It has. Also, MOS switches 44 and 45, which are switch units, are provided in series with the primary coil 51 and the like, and a controller 53, which is a second control device that operates the MOS switches, is provided. Further, a rectifying circuit 5 for rectifying the alternating current
4 and 55, and smoothing capacitors 56 and 57 for smoothing the current passing through the rectifier circuits 54 and 55.

Here, the fifth switch element is a MOS switch 44, and the fifth switch element is a MOS switch 45.

3.2 Operation The operation of the half-bridge switching power supply circuit will be described below.

A control voltage for each MOS switch is applied as shown in FIG. 6B. Hereinafter, description will be given in accordance with the lapse of time T0 to T4.

At times T0 to T1, a second current, which is a current in the direction of arrow E in FIG. 6A, flows through the saturable reactor 42. Therefore, the saturable reactor 42 exhibits the low impedance state 1 in FIG. 3, and a current flows in the direction of arrow G in FIG. 6A, and the saturable reactor 42 is separated from the secondary coil 52 by the action of electromagnetic induction between the primary coil 51 and the secondary coil 52. Load is output.
Further, since current also flows through the auxiliary coil 43, electric energy is stored. Further, electric charges are accumulated in the MOS switch 45.

When the current in the direction of arrow E stops at time T1, the electric energy stored in auxiliary coil 43 tends to move in the direction of arrow F with respect to saturable reactor. At this time, the polarity of the saturable reactor 42 is inverted, and the saturable reactor 42 exhibits the high impedance state 1 shown in FIG. 3, so that the electric energy stored in the auxiliary coil 43 is prevented from moving to the primary coil 51. Accordingly, the electric energy moves in the direction of the MOS switches 44 and 45, so that the electric charge accumulated in the MOS switch 45 at the time T0 to T1 is discharged. At time T2, the MOS switch 45 can be turned ON in a state where the electric charge is not charged.

In the time T1 to T2, the MOS switch 44 is charged.

At the time T2, the saturable reactor 42 does not reach the saturation state 1 in FIG.
T2 (dead time) is determined.

During the time T2 to T3, the saturable reactor 42 is in the low impedance state 2 in FIG. 3, so that a current flows in the direction of arrow H in FIG.
The load is output from the secondary coil 52 by the action of electromagnetic induction between the secondary coil 52 and the secondary coil 52. The auxiliary coil 43 stores electric energy, and the MOS switch 44 stores electric charge.

When the current in the direction of arrow F stops at time T3, the electric energy stored in auxiliary coil 43 tends to move in the direction of arrow E with respect to saturable reactor 42. At this time, the polarity of the saturable reactor 42 is inverted, and the saturable reactor 42 exhibits the high impedance state 2 shown in FIG. 3, so that the electric energy stored in the auxiliary coil 43 is prevented from moving to the primary coil 51. Therefore, the electric energy moves in the direction of the MOS switch 44, so that the time T
The charge accumulated in the MOS switch 44 in 2 to T3 is discharged. At time T4, the MOS switch 44 can be turned on in a state where the electric charge is not charged.

In a period from time T3 to time T4, the MOS switch 45 is charged.

It is to be noted that, at the time T4, the saturable reactor 42 is set at the time T3 to the time T3 so as not to reach the saturated state 2 in FIG.
T4 (dead time) is determined.

Therefore, even under a light load, the MOS switch can be turned on in a state where no electric charge is stored.
The generation of steep charge / discharge current can be suppressed, and noise and switching loss can be reduced.

[Brief description of the drawings]

FIG. 1 is a functional block diagram according to a first embodiment.

FIG. 2 is a diagram illustrating an overall configuration and a waveform of a control voltage of a MOS switch according to the first embodiment.

FIG. 3 is a diagram showing a hysteresis characteristic of a saturable reactor.

FIG. 4 is a diagram showing a voltage waveform at a point A in FIG. 2;

FIG. 5 is a diagram illustrating a voltage waveform at a point B in FIG. 2;

FIG. 6 is a diagram illustrating an overall configuration and a waveform of a control voltage of a MOS switch according to a second embodiment.

FIG. 7 is a diagram showing waveforms of control voltages of a conventional switching power supply circuit and a switch element.

8 is a diagram showing a voltage waveform at point A in FIG. 7;

FIG. 9 is a diagram showing a switching power supply circuit when a conventional auxiliary coil is used.

FIG. 10 is a diagram showing a voltage waveform at a point A in FIG. 9;

[Explanation of symbols]

 21 Transformer 22, 23 Saturable reactor 24 Auxiliary coil 25, 26, 27, 28 MOS switch 31 Primary coil 32 Secondary coil 33 controller

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H007 AA01 AA03 CA02 CB05 CC32 DB01 HA01 5H730 AA01 AA10 AA14 BB27 CC01 DD04 DD16 ZZ16

Claims (10)

[Claims] A primary coil and a secondary coil opposed to each other, a load output section for outputting a load from the secondary coil by an electromagnetic induction effect generated by a current flowing through the primary coil, and having a parasitic capacitance. And a switch unit for determining an energized state and a non-energized state in the primary coil. In the energized state, a low impedance state is provided between the switch unit and the primary coil in the energized state. Variable energy means for providing a high impedance state between the switch unit and the primary coil when shifting to a non-energized state, and an energy storage unit capable of storing electric energy between the variable impedance means and the switch unit The variable impedance at the time of transition from the energized state to the non-energized state. The electric impedance stored in the energy storage section in the energized state is suppressed from moving to the load output section by the high impedance state of the dancer, and the electric energy stored in the energy storage section in the energized state is suppressed. A switching power supply circuit for discharging electric charges accumulated in a parasitic capacitance in the switch unit in the energized state by moving to the switch unit. 2. The switching power supply circuit according to claim 1, wherein the electric energy stored in the energy storage unit in the energized state moves to the switch unit to charge a parasitic capacitance in the switch unit. Characterized by that. 3. The switching power supply circuit according to claim 1, wherein said energy storage section is provided in parallel with said primary coil and said variable impedance means. 4. The switching power supply circuit according to claim 3, wherein the switch section includes first, second, third and fourth switch elements, and the first and second switch elements exhibit a connected state, When the third and fourth switch elements are in the disconnected state, a first current is supplied to the primary coil, the energy storage unit and the variable impedance means, and the third and fourth switch elements are connected. State, and when the first and second switch elements are in the disconnected state, a current is supplied to the primary coil, the energy storage section, and the variable impedance means in a direction opposite to the first current. When the first, second, third, and fourth switch elements are in a disconnected state, no current is supplied to the primary coil, the energy storage unit, and the variable impedance means. 5. The switching power supply circuit according to claim 4, wherein said first, second, third and fourth switch elements are controlled so as to exhibit the following states (1) to (3). A device comprising a device. (1) Joint state of first and second switch elements, disconnected state of third and fourth switch elements (2) Disconnected state of first, second, third, and fourth switch elements (3) No. Joint state of third and fourth switch elements, disconnection state of first and second switch elements 6. The switching power supply circuit according to claim 1, wherein the switch section includes a fifth switch element and a sixth switch element, wherein the fifth switch element is in a connected state, and a sixth switch is provided. When the element is turned off, a second current is supplied to the primary coil, the energy storage unit, and the variable impedance means, the fifth switch element is turned off, and the sixth switch element is connected. When a state is exhibited, a current is supplied to the primary coil, the energy storage unit, and the variable impedance means in a direction opposite to the second current, and the fifth and sixth switch elements are turned off. At the time, no current is supplied to the primary coil, the energy storage unit, and the variable impedance means. 7. The switching power supply circuit according to claim 6, further comprising a second control device that controls the fifth and sixth switch elements to exhibit the following states (1) to (3). What to do. (1) Fifth switch element connection state, sixth switch element disconnection state (2) Fifth and sixth switch element disconnection states (3) Sixth switch element connection state, fifth switch Element disconnection state 8. The switching power supply circuit according to claim 1, wherein said variable impedance means has a magnetic hysteresis characteristic. 9. The switching power supply circuit according to claim 1, wherein said variable impedance means is a coil using an amorphous core. 10. The switching power supply circuit according to claim 1, wherein said variable impedance means comprises a first variable impedance means and a second variable impedance means, and said first variable impedance means comprises: The second variable impedance means is provided at one end of the primary coil, and the second variable impedance means is provided at the other end of the primary coil.