JP2003164152A - Switching power unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching power unit that uses a plurality of converters in series and is capable of properly switching an output voltage Vo. <P>SOLUTION: The switching power unit comprises: a transformer 1; a first converter 2 and a second converter 3 connected in series between a power input end and a primary winding of the transformer 1; output circuits 7, 31 connected to a secondary winding of the transformer 1; and control circuits 32, 33 for controlling operations of the first and second converters 2, 3. The control circuits 32, 33 duty-control the first converter 2 and frequency-control the second converter 3. BY such a configuration, the switching of the output voltage can easily be conducted by easy control when a user switches the output voltage. <P>COPYRIGHT: (C)2003,JPO

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, and more particularly to a switching power supply device using a plurality of converters in series.

[0002]

2. Description of the Related Art In recent years, a series circuit of a buck converter circuit and a half bridge circuit is used as a primary side circuit of a switching power supply device, a buck converter circuit steps down an input voltage Vin, and this is supplied to a half bridge circuit. A method to excite the primary winding of a transformer by a half bridge circuit that receives (Buck + H
alf Bridge (d = 50%) Topology Applied to very Low Vo
ltage Power Converters, IEEE APEC, 2001, Session 1
9.4).

When such a circuit is used as the primary side circuit of the switching power supply device, the duty of the switching element included in the half bridge circuit is fixed to a fixed amount, while the switching element included in the buck converter circuit is fixed. The duty of is controlled to a predetermined amount based on the output voltage Vo. As a result, a relatively low voltage can be obtained as the output voltage Vo with high efficiency and stability, so that it can be optimally used, for example, as a power supply for a computer.

FIG. 3 is a circuit diagram of a conventional switching power supply device having such a primary side circuit.

As shown in FIG. 3, the conventional switching power supply device includes a transformer 1, a buck converter circuit 3 connected to the input power supply 2, and a primary winding of the transformer 1 connected to the buck converter circuit 3. An output voltage via a half bridge circuit 4 for exciting, a rectifying circuit 5 provided on the secondary side of the transformer 1, a smoothing circuit 7 provided at a subsequent stage of the rectifying circuit 5 and connected to a load 6, and an insulating circuit 8. Vo is monitored and on / off of the first and second main switches 9 and 10 included in the buck converter circuit 3 is controlled based on the Vo, and the third voltage included in the half bridge circuit 4 is controlled.
And a control circuit 13 for controlling on / off of the fourth main switches 11 and 12.

The buck converter circuit 3 includes first and second buck converter circuits.
In addition to the main switches 9 and 10, the inductor 14 is provided, and the half bridge circuit 4 includes the buck converter circuit 3 in addition to the third and fourth main switches 11 and 12.
Of the third and fourth main switches 11 and 12 and the first and second input capacitors 1 and 16 which are connected in series between the output terminals of the first and second main switches 11 and 12.
The primary winding of the transformer 1 is connected between the nodes 5 and 16. The rectifier circuit 5 is composed of first and second diodes 17 and 18, and the smoothing circuit 7 is composed of a smoothing inductor 19 and a smoothing capacitor 20. The rectifier circuit 5 and the smoothing circuit 7 form an output circuit.

In such a configuration, the first and second main switches 9 included in the buck converter circuit 3,
Under the control of the control circuit 13, the switch 10 is alternately turned on with a predetermined dead time, whereby the input voltage Vin1 and the first and second main switches are provided between the output terminals of the buck converter circuit 3. A constant internal voltage Vin2 determined by the duty of 9, 10 appears. On the other hand, the third and fourth main switches 11 and 12 included in the half bridge circuit 4, under the control of the control circuit 13,
Both are alternately turned on / off with a fixed amount of duty
Turn off. As a result, the internal voltage V
A constant output voltage Vo determined by the turn ratio of in2 and the transformer 1 is applied.

[0008]

However, in order to drive different types of loads by one switching power supply device, it is sometimes required that the user can switch the value of the output voltage Vo. For example, depending on the user, the output voltage Vo may be 3.3V or 1.5V.
In the conventional switching power supply device shown in FIG. 3, the range to be stepped down by the buck converter circuit 3 which is the first-stage converter becomes large and the output voltage Vo becomes lower than the output voltage Vo. There is a problem in that the load on the buck converter circuit 3 is large when (for example, 1.5 V) is required, and the loss increases.

On the other hand, when the value of the output voltage Vo is set lower by the user, not only the duty of the buck converter circuit 3 but also the duty of the half bridge circuit 4 which is the second-stage converter is reduced, It is also possible to reduce the output voltage Vo. However, in this case, since the plurality of converters perform the stabilizing operation of the output voltage Vo, the stability of the output voltage Vo may be impaired. In order to prevent this, the operation between these converters is appropriately adjusted. There is a need to. Therefore, control becomes complicated. In particular, when a transistor is used as a rectifying element that constitutes a rectifying circuit and the secondary side voltage of the transformer 1 is used to turn on / off, if the duty of the half bridge circuit 4 changes, the half bridge circuit 4 changes accordingly. Since the dead time varies, the loss generated in the rectifier circuit increases. That is, when the duty of the half bridge circuit 4 is reduced in response to a request for a lower voltage (for example, 1.5 V) as the output voltage Vo, the dead time of the half bridge circuit 4 increases, so the transformer 1 Therefore, the period during which no voltage is generated on the secondary side becomes long. Therefore, the conduction period of the rectification transistor that constitutes the rectification circuit is shortened accordingly, and the current flows through the body diode for a long period.

Therefore, an object of the present invention is to provide a switching power supply device using a plurality of converters in series,
An object of the present invention is to provide a switching power supply device that can appropriately switch the output voltage Vo.

Another object of the present invention is to provide a switching power supply device using a plurality of converters in series, which is capable of switching the output voltage Vo by simple control. Is.

Still another object of the present invention is a switching power supply device using a plurality of converters in series, and switching the output voltage Vo while suppressing an increase in loss generated in a rectifier circuit. It is to provide a switching power supply device capable of

[0013]

The object of the present invention is to:
A transformer; first and second converters connected in series between a power supply input terminal and a primary winding of the transformer; an output circuit connected to a secondary winding of the transformer; And a control circuit for controlling the operation of the second converter, wherein the control circuit duty-controls the first converter and frequency-controls the second converter. To be achieved.

According to the present invention, while the duty of the first converter is controlled and the frequency of the second converter is frequency controlled, even if the user requests the switching of the output voltage, this is controlled. It can be performed by simple control.

In a preferred embodiment of the present invention, the control circuit controls the duty of the first converter on the basis of the current output voltage output from the output circuit, while irrespective of the current output voltage. , And controls the operating frequency of the second converter based on the set value.

According to a preferred embodiment of the present invention, the first
Since the converter and the second converter are assigned the roles, it is not necessary to make fine adjustments between them.

In a further preferred aspect of the present invention, the control circuit controls the second converter such that the dead time becomes constant regardless of the operating frequency.

[0018] In a further preferred aspect of the present invention, the output circuit includes a self-drive type synchronous rectification circuit including a rectification transistor, wherein the dead time is calculated from an operation delay time of the rectification transistor. It is set to be substantially equal to the period obtained by subtracting the commutation period due to the transformer leakage.

According to a further preferred embodiment of the present invention, it becomes possible to effectively suppress the loss generated in the output circuit while preventing the generation of the through current.

In a further preferred aspect of the present invention, the first converter is a buck converter circuit and the second converter is a half-bridge circuit.

[0021]

DETAILED DESCRIPTION OF THE INVENTION Referring to the accompanying drawings,
A preferred embodiment of the present invention will be described in detail.

FIG. 1 is a circuit diagram of a switching power supply device 30 according to a preferred embodiment of the present invention.

As shown in FIG. 1, the switching power supply device 30 according to the present embodiment is similar to the conventional switching power supply device in that it uses a series circuit of a buck converter circuit and a half bridge circuit as a primary side circuit. The device is different in that the rectifier circuit 5 included in the conventional switching power supply device is replaced with the rectifier circuit 31 and control circuits 32 and 33 are included in place of the control circuit 13 included in the conventional switching power supply device. Since other configurations are similar to those of the conventional switching power supply device, the same components as those of the conventional switching power supply device are designated by the same reference numerals as those in FIG. 3, and the description thereof will be omitted.

The rectifying circuit 31 is composed of first and second rectifying transistors 41 and 42, the gates of which are:
It is connected between the other rectifying transistor and the secondary winding of the transformer 1. As a result, the ON / OFF of the first and second rectifying transistors 41 and 42 is automatically controlled by the voltage generated in the secondary winding of the transformer 1. That is, the rectifier circuit 31 is a self-drive type synchronous rectifier circuit.

The control circuit 32 receives a control signal S given by the user in addition to the output voltage Vo supplied through the insulating circuit 8 so that the output voltage Vo has a voltage value indicated by the control signal S. The control pulses Vgs9 and Vgs10 to be supplied to the gate electrodes of the first and second main switches 9 and 10 included in the buck converter circuit 3 are generated. Here, the control signal S may be any signal capable of selecting at least two types of output voltage Vo, but in the present embodiment, a 1-bit digital signal is used as the control signal S, and this is a high level. In this case, it is indicated that the output voltage Vo (Vo1) should be 3.3V, and when it is low level, the output voltage Vo (Vo2) should be 1.5V.
Indicates what to do. However, the present invention is not limited to this, and for example, by using a digital signal of 2 bits or more as the control signal S, three or more kinds of output voltages Vo may be selectable. Further, an analog signal may be used as the control signal S, and the output voltage Vo to be generated based on the voltage value (or current value) may be linearly indicated.

In addition, the control pulse Vg by the control circuit 32
The control of s9 and Vgs10 is so-called duty control, and the buck converter circuit 3 is controlled by adjusting the conduction period of these while the frequency is fixed.

The control signal 33 receives the control signal S,
Based on this, the control pulses Vgs11 and Vgs12 to be supplied to the gate electrodes of the third and fourth main switches 11 and 12 included in the half bridge circuit 4 are generated.
More specifically, the half bridge circuit 4 is controlled by adjusting these frequencies with the dead time DT fixed based on the voltage value indicated by the control signal S. That is, the control circuit 33 controls the frequency of the half bridge circuit 4.

FIG. 2 is a timing chart for explaining the operation of the control circuit 33.

As shown in FIG. 2, when the control signal S is at high level, the control pulses Vgs11 and Vgs1 are generated.
The frequency of 2 is set to f1, and when the control signal S is at a low level, the frequencies of the control pulses Vgs11 and Vgs12 are set to f2 (<f1). , Control pulses Vgs11, Vg
The period in which s12 is low level, that is, the dead time DT is controlled to be constant. As a result, the duty when the control signal S is low level is lower than the duty when the control signal S is high level. Therefore, when the control signal S becomes low level, the step-down level is reduced by the half bridge circuit 4. growing.

Here, how to set the frequency f1 when the control signal S is at the high level and the frequency f2 when the control signal S is at the low level depends on whether the control signal S is at the high level. The output voltage Vo1 to be generated, the output voltage Vo2 to be generated when the control signal S is at a low level, and the fixed dead time DT are determined based on the ratio of the output voltage Vo1 and Vo2. Is preferably set to substantially match the ratio of the duty when the control signal S is at the low level and the duty when the control signal S is at the low level. By setting the frequencies f1 and f2 in this way, the step-down level by the buck converter 3 can be made substantially constant regardless of the level of the control signal S.

Further, the dead time DT is determined based on the operation delay times of the first and second rectifying transistors 41 and 42, and the first and second rectifying transistors 41 are set.
It is preferable to set it so that it substantially coincides with the period obtained by subtracting the commutation period due to the transleakage of the transformer 1 from the operation delay times of and 42. Where the first and second
The operation delay time of the rectifying transistors 41 and 42 of
It is defined by the time required from when the gate-source voltages of the first and second rectifying transistors 41 and 42 fall below the threshold value until when they are actually turned off.

If the dead time DT is set to substantially match the operation delay time of the first and second rectifying transistors 41 and 42 minus the commutation period due to the trans leakage of the transformer 1, Through current does not flow through the first and second rectifying transistors 41 and 42, and the first and second rectifying transistors 41 and 4 do not flow.
It is possible to reduce the current flowing through the second body diode as much as possible.

At this time, the dead time DT is set to be substantially longer than the operation delay time of the first and second rectifying transistors 41 and 42 minus the commutation period due to the trans leakage of the transformer 1, and the margin is set. You may give it. In this case, current flows through the body diodes of the rectifying transistors 41 and 42 by the margin, and therefore it is preferable to set the margin to the minimum necessary.

With the above configuration, in the switching power supply device 30 according to the present embodiment, when driving a load having an operating voltage of 3.3V, the control signal S is set to a high level and the operating voltage is 1. When driving a load of 5V, it is possible to drive any load by setting the control signal S to a low level. In this case, switching of the output voltage Vo (3.3 V or 1.
Since 5 V) is achieved by switching the operating frequency in the half bridge circuit 4, the buck converter circuit 3 is substantially effective even when the required output voltage Vo is set low (1.5 V). Since it is not necessary to increase the step-down level, it is possible to prevent the burden from increasing.

In the switching power supply device 30 according to this embodiment, the output voltage Vo is switched by switching the operation of the half bridge circuit 4, and the output voltage Vo is stabilized by the operation of the buck converter circuit 3. Since the roles are shared between the two, it is not necessary to finely adjust the operation of the buck converter circuit 3 and the operation of the half bridge circuit 4, and to suppress the complication of control. Is possible.

Moreover, in the switching power supply device 30 according to the present embodiment, the dead time DT of the half bridge circuit 4 is set to the first and second rectification transistors 41 and 4.
If the operation delay time of No. 2 is substantially equal to the period obtained by subtracting the commutation period due to the transformer leakage of the transformer 1, the rectification transistor 4 is prevented while the generation of the through current is prevented.
It is possible to reduce the current flowing through the body diodes 1 and 42 as much as possible. Therefore, the loss generated in the rectifier circuit 31 can be effectively suppressed.

The present invention is not limited to the above embodiments, and various modifications can be made within the scope of the invention described in the claims, and these are also included in the scope of the present invention. It goes without saying that it is a thing.

For example, in the switching power supply device 30 according to the above embodiment, the series circuit of the buck converter circuit 3 and the half bridge circuit 4 is used as the primary side circuit of the transformer 1, but it is applicable to the present invention. However, the primary side circuit is not limited to this, and other converter circuits may be used in series. For example, instead of the buck converter circuit 3, another circuit such as a boost converter circuit, a forward converter circuit, a full bridge, or a push pull circuit may be used.

Further, in the switching power supply device 30 according to the above-mentioned embodiment, the rectifier circuit 31 composed of the first and second rectifier transistors 41 and 42 is used as the secondary side circuit of the transformer 1. In the invention, the secondary side circuit of the transformer 1 is not particularly limited, and another type of circuit, for example, a rectifying circuit using a diode may be used.

Further, in the switching power supply device 30 according to the above embodiment, a 1-bit digital signal is used as the control signal S, and when this is at a high level, the frequencies of the control signals Vgs11 and Vgs12 are set to f1,
When it is at a low level, it is set to f2 (> f1). However, when a digital signal of 2 bits or more is used as the control signal S, for example, when four kinds of output voltage Vo can be selected, Depending on the control signals Vgs11, Vg
The frequency of s12 may be set in four steps. When an analog signal is used as the control signal S and the output voltage Vo can be linearly selected based on the voltage value (or current value) of the analog signal, the control signals Vgs11 and Vg are correspondingly selected.
The frequency of s12 may be set linearly.

[0041]

As described above, according to the present invention,
It is possible to provide a switching power supply device that can switch the output voltage Vo by simple control and that suppresses an increase in loss that occurs in the rectifier circuit.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a switching power supply device 30 according to a preferred embodiment of the present invention.

FIG. 2 is a timing chart for explaining the operation of the control circuit 33.

FIG. 3 is a circuit diagram of a conventional switching power supply device.

[Explanation of symbols]

1 transformer 2 Input power 3 Buck converter circuit 4 Half bridge circuit 5 Rectifier circuit 6 load 7 Smoothing circuit 8 insulation circuit 9 First main switch 10 Second main switch 11 Third main switch 12 Fourth main switch 13 Control circuit 14 inductor 15 First input capacitor 16 Second input capacitor 17 First diode 18 Second diode 19 Smoothing inductor 20 Smoothing capacitor 30 switching power supply 31 Rectifier circuit 32, 33 control circuit 41 First Rectifying Transistor 42 Second rectifying transistor

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Toshiyuki Zaitsu             1-13-1, Nihonbashi, Chuo-ku, Tokyo             -In DC Inc. (72) Inventor Katsuhiko Shimizu             1-13-1, Nihonbashi, Chuo-ku, Tokyo             -In DC Inc. F-term (reference) 5H006 AA02 CA02 CB07 CC02                 5H730 AA14 AS01 BB13 BB26 BB57                       BB86 BB88 CC25 DD04 EE08                       EE14 FD01 FG05 FG07 FG15                       FV05

Claims (5)

[Claims] 1. A transformer, first and second converters connected in series between a power supply input terminal and a primary winding of the transformer, and an output circuit connected to a secondary winding of the transformer. And a control circuit for controlling the operations of the first and second converters, wherein the control circuit duty-controls the first converter and frequency-controls the second converter. Switching power supply. 2. The control circuit controls the duty of the first converter on the basis of the current output voltage output from the output circuit, while based on the set value regardless of the current output voltage. The switching power supply device according to claim 1, wherein the operating frequency of the second converter is controlled. 3. The switching power supply device according to claim 1, wherein the control circuit controls the second converter so that the dead time becomes constant regardless of the operating frequency. 4. The output circuit includes a self-drive type synchronous rectification circuit composed of a rectification transistor, and the dead time is a commutation period due to a transleakage of the transformer from an operation delay time of the rectification transistor. 4. The switching power supply device according to claim 3, wherein the switching power supply device is set to be substantially equal to the period obtained by subtracting. 5. The switching power supply device according to claim 1, wherein the first converter is a buck converter circuit and the second converter is a half bridge circuit.