JP2004260928A - Switching power supply device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the efficiency of a switching power supply device by suppressing copper loss and iron loss at a leakage inductance when applied with a light load, in the switching power supply device. <P>SOLUTION: The switching power supply device comprises a transformer 4, a switching circuit 3, the leakage inductance 8, an output circuit 6, and a control circuit 7. The switching power supply device detects the state of the load, and according to the result, controls the leakage inductance to be large when the load is light in weight, and small when the load is heavy in weight. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a switching power supply device that includes a full-bridge type switching circuit and controls a switch in the switching circuit by a phase shift control method.
[0002]
[Prior art]
Conventionally, a DC-DC converter has been known as a switching power supply device. Typically, a DC-DC converter temporarily converts a DC input into an AC using a switching circuit, transforms the DC input (step-up or step-down) using a transformer, and converts the DC into a DC using an output circuit. It is a device to convert. As a result, a DC output having a voltage different from the input voltage is obtained. Here, a full bridge circuit is used as a switching circuit of a switching power supply that requires a large capacity. A phase shift control method is known as a drive method capable of reducing switching loss generated in this type of switching circuit (for example, see Patent Document 1).
[0003]
FIG. 9 is a circuit diagram showing a conventional switching power supply device. The conventional switching power supply device includes an input capacitor 2 connected between both ends of an input power supply 1 and first to fourth switches Q1 to Q4. It includes a switching circuit 3, a transformer 4, a rectifier circuit 5 including diodes 51 and 52, a smoothing circuit 6 including an inductor 61 and a capacitor 62, and a control circuit 7 for controlling the operation of the switching circuit 3. Further, a leakage inductance 8 exists between the switching circuit 3 and the transformer 4. Diodes d1 to d4 and capacitors c1 to c4 exist as parasitic elements in parallel between the source and drain of each of the switches Q1 to Q4. Reference numeral 9 denotes a load connected to an output circuit including the rectifier circuit 5 and the smoothing circuit 6.
[0004]
The control circuit 7 generates the gate pulses VG1 to VG4 by a phase shift control method. The switching circuit 3 operates in response to the gate pulses VG1 to VG4 from the control circuit 7.
[0005]
FIG. 10 is a timing chart showing the operation of the conventional switching power supply device. As shown in FIG. 10, in the phase shift control, the gate pulses VG1 and VG2 alternately go to a high level with a predetermined dead time interposed therebetween. The gate pulse VG3 is phase shifted with respect to the gate pulse VG2, and the gate pulse VG4 is phase shifted with respect to the gate pulse VG1. The waveform of the voltage VT on the primary side of the transformer 4 is determined by the phase shift amount of the gate pulse VG4 with respect to the gate pulse VG1, and the phase shift amount of the gate pulse VG3 with respect to the gate pulse VG2. Specifically, in a period in which the gate pulses VG1 and VG4 are both at the high level as in the period t1, both the first switch Q1 and the fourth switch Q4 are in the ON state, so that The primary side voltage VT becomes the voltage -Vin of the input power supply, while the second switch Q2 and the third switch Q3 are in the period in which the gate pulses VG2 and VG3 are both at the high level as in the period t4. Are both in the ON state, the primary voltage VT of the transformer 4 becomes the voltage Vin of the input power supply. In other periods, the primary voltage VT of the transformer 4 is zero.
[0006]
Therefore, the power transmitted to the secondary side of the transformer 4 is determined by the phase shift amount of the gate pulse VG4 with respect to the gate pulse VG1 and the phase shift amount of the gate pulse VG3 with respect to the gate pulse VG2. When the voltage of the input power supply is increased or the load is lightened, the amount of phase shift is increased, and the period during which both the gate pulses VG1 and VG4 are at the high level and the gate pulses VG2 and VG3 are both at the high level Shorten the level period. When the voltage of the input power supply becomes small or the load becomes heavy, the phase shift amount is reduced, and a period in which both the gate pulses VG1 and VG4 are at a high level and a period in which both the gate pulses VG2 and VG3 are at a high level Lengthen.
[0007]
In the switching power supply device, for example, as shown by the period t1, both the gate pulses VG1 and VG4 become high level, and both the first switch Q1 and the fourth switch Q4 are turned on, so that the secondary side of the transformer 4 When the first switch Q1 is turned off by setting the gate pulse VG1 to the low level as shown by a period t2 after the energy is transmitted to the second switch Q2, the parasitic energy of the second switch Q2 is utilized. The electric charge stored in the capacitor c2 is extracted, a current flows through the parasitic diode d2, and then the second switch Q2 is turned on to perform zero volt switching (hereinafter, referred to as ZVS). Such a zero volt switching operation utilizes the excitation energy of the leakage inductance 8, thereby reducing switching loss and improving the efficiency of the switching power supply device. However, the excitation energy is Ls the value of the leakage inductance of the leakage inductance 8, when the current flowing therethrough and I (1/2) because represented by Ls · I ^2, when the current I as a light load is small Then, in order to perform ZVS, it is necessary to increase the value of the leakage inductance Ls. When the value of the inductance is increased, copper loss, iron loss and the like naturally increase, and the efficiency of the switching power supply device decreases.
[0008]
The reason why ZVS cannot be achieved when the leakage inductance 8 is small at a light load will be briefly described using switches Q2 and Q3. The same applies to the switches Q1 and Q4. When the leakage inductance 8 is small and the load 9 is light, the energy stored in the leakage inductance 8 is small. Therefore, only by extracting the charge of the parasitic capacitance of the switch Q2, the current IT flowing through the leakage inductance 8 is greatly reduced, and the switch Q3 Becomes zero before the charge of the parasitic capacitance is completely extracted, and conversely, is recharged by the input voltage Vin, and the source-drain voltage Vds of the switch Q3 that has once dropped rises. As a result, ZVS of the switch Q3 cannot be performed. Further, when the load 9 is lightened or the leakage inductance 8 is small, the parasitic capacitance of the switch Q2 is not pulled out, and the switches Q2 and Q3 cannot perform ZVS.
[0009]
[Patent Document 1]
JP-A-2003-18857
[0010]
[Problems to be solved by the invention]
Therefore, an object of the present invention is to solve the problem of improving the efficiency in the switching power supply by suppressing the copper loss and the iron loss in the leakage inductance while enabling the ZVS at a light load in the switching power supply. .
[0011]
[Means for Solving the Problems]
The present invention includes a transformer, first and second arms connected in parallel to an input power supply, and each arm includes a series configuration of switches on a high potential side and a switch on a low potential side, and each switch A full-bridge type switching circuit including a diode and a capacitor each configured in parallel with each other; a connection portion between both high-potential side and low-potential side switches in one arm of the switching circuit; and a primary winding of the transformer. A switching power supply device including an inductance present in a current path between the output circuit and an output circuit provided on the secondary side of the transformer, and a control circuit that performs phase shift control on the operation timing of each switch of the switching circuit. When the load is light, the inductance is large, and when the load is heavy, the inductance is small. And controlling.
[0012]
The phase shift control circuit and the control circuit may be constituted by separate circuits or may be constituted by the same circuit. Each switch in the switching circuit can be configured by an element including a diode and a capacitor as a parasitic element between a source and a drain, such as a MOSFET.
[0013]
According to the present invention, the inductance is controlled to be large when the load is light, and the inductance is controlled to be small when the load is heavy. Therefore, when the current flowing through the inductance is small at the time of light load, the value of the inductance is increased. Therefore, a large excitation energy is generated in the inductance, and zero-volt switching can be performed with high reliability. On the other hand, when the load is heavy, the inductance value can be controlled to be small. As a result, in the present invention, unlike the conventional case, it is possible to prevent the loss such as copper loss and iron loss due to the leakage inductance from increasing due to the increase in the load, thereby greatly improving the efficiency of the entire switching power supply device. I do.
[0014]
In a preferred embodiment of the present invention, the control circuit detects a state of a load connected to the output circuit, and as a result of the detection, increases the inductance when the load is light, and increases the inductance when the load is heavy. Is controlled to be small.
[0015]
In a further preferred aspect of the present invention, an inductor is connected to a current path between the switching circuit and a primary winding of the transformer, and an open / close switch is connected in parallel to the inductor. When the load is light, the on / off switch is turned off and the inductor is connected to the current path. When the load becomes heavy, the on / off switch is turned on and the inductor is electrically short-circuited.
[0016]
In a further preferred aspect of the present invention, the switching circuit has at least two switching circuits, and each switching circuit has a different inductance value between each first arm and a primary winding of the transformer. While the inductance is present, the respective second arms are shared with each other, and the control circuit selects a switching circuit having a large inductance when the load is light, and selects an inductance circuit when the load is heavy. Is controlled so as to select the switching circuit on the smaller side.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, details of the present invention will be described based on embodiments shown in the drawings.
[0018]
A switching power supply according to an embodiment of the present invention will be described with reference to FIGS. 1 is a circuit diagram of a switching power supply device, FIG. 2 is a timing chart for explaining the operation of FIG. 1, FIG. 3 is a diagram showing a current path flowing to each part in FIG. 1, and FIG. FIG. 5 is a graph showing a change in the voltage waveform of each part when the leakage inductance is switched from small to large at a light load, and FIG. 6 is a graph showing a characteristic between the load and the efficiency of the switching power supply. FIG. Parts corresponding to those in FIGS. 9 and 10 are denoted by the same reference numerals, and description of the parts corresponding to the same reference numerals is omitted.
[0019]
Referring to these figures, 1 is an input power supply, 2 is an input capacitor, 3 is a switching circuit, 4 is a transformer, 5 is a rectifier circuit, 6 is a smoothing circuit, 7 is a control circuit, 8 is a leakage inductance, and 9 is a load. Are respectively shown. In the switching circuit 3, each of the switches Q1 to Q4 is formed of a MOSFET, and the first and second switches Q1 and Q2 form a first arm, and the third and fourth switches Q3 and Q3 are formed. Q4 constitutes the second arm. The first and third switches Q1 and Q3 together constitute a high-potential side switch, and the second and fourth switches Q2 and Q4 together constitute a low-potential side switch. Parasitic diodes d1 to d4 and capacitors c1 to c4 are connected in parallel between the sources and drains of the switches Q1 to Q4, respectively.
[0020]
The control circuit 7 includes a phase shift amount generator 72, a gate pulse generator 71, a switching load data storage 73, a detector 74, and a switching signal generator 75. In the control circuit 7, assuming that a function equivalent to that of the conventional circuit is achieved, a phase shift amount generating section 72 generates a signal relating to a phase shift amount in response to an output control signal, and the gate pulse generating section 71 , The gate pulses VG1 to VG4 for the respective gates of the switches Q1 to Q4 are output.
[0021]
In the present embodiment, the control circuit 7 further includes a switching load data storage unit 73, a detection unit 74, and a switching signal generation unit 75, and further includes an external inductance 10 and an external switch 11. It has a special feature.
[0022]
The external inductance 10 is connected in series between the interconnection of the switches Q3 and Q4 in one arm of the switching circuit 3 and the primary winding of the transformer 4. The external switch 11 is preferably composed of a MOSFET, and is connected in parallel with the external inductance 10.
[0023]
In the control circuit 7, the data storage unit 73 stores data for switching the external switch 11 to the off side when the load 9 is light and to the on side when the load 9 is heavy.
[0024]
The detection unit 74 detects the state of the load 9 from the current IT flowing through the primary winding of the transformer.
[0025]
The switching signal generator 75 compares the data stored in the data storage 73 with the data detected by the detector 74, and generates a switching signal for turning off the external switch 11 when the load 9 is light, so that the leakage inductance 8 is generated. On the other hand, the external inductance 10 is connected in series to increase the value of the whole inductance, and when the load 9 is heavy, a switching signal for turning on the external switch 11 is generated to short-circuit the external inductance 10 and to reduce the whole inductance. Is controlled to be small.
[0026]
Here, it is not essential that the control circuit 7 has a function of detecting the state of the load 9, and the output of another circuit that detects the state of the load 9 may be used.
[0027]
The configuration of each part of the control circuit 7 may be configured by software including a microcomputer or the like.
[0028]
The operation will be described with reference to FIGS.
[0029]
2, VG1, VG2, VG3, and VG4 are gate pulses, VT is a transformer primary side voltage, IT is a current, Q2Vds is a source-drain voltage of the switch Q2, Q3Vds is a drain-source voltage of the switch Q3, Q2Id indicates the drain current of the switch Q2, and Q3Id indicates the waveform of the drain current of the switch Q3.
[0030]
FIG. 3 shows the flow of the current IT at each of the timings t1 to t7. In FIG. 3, it is assumed that the leakage inductance 8 is included in the primary winding of the transformer 4. The operation related to the phase shift of the gate pulses VG1 to VG4 has been described with reference to FIG.
[0031]
In the period t1, the switches Q1 and Q4 are both turned on, the current IT flows through the primary winding of the transformer through a path shown by (t1) in FIG. 3, and energy is transmitted to the secondary side of the transformer. You. At this time, the parasitic capacitance of the switches Q2 and Q3 is almost charged to the input power supply voltage Vin. When the switch Q1 is turned off, a current flows through the parasitic capacitance of each of the switches Q2 and Q4 through a path shown by (t2) in FIG. 3 due to the back electromotive force of the leakage inductance 8, and the charge of the parasitic capacitance of the switch Q2 is extracted. Go. When the charge of the parasitic capacitance of the switch Q2 is extracted and the charge is almost eliminated, and the voltage Vds between the source and the drain of the switch Q2 becomes close to zero V, the current IT flows through the diode of the switch Q2 through the path shown by (t3) in FIG. Will flow through. As a result, the source-drain voltage Vds of the switch Q2 decreases from Vin to almost 0V. At this timing, the switch Q2 is turned on to perform ZVS.
[0032]
Next, when the switch Q4 is turned off, the current IT extracts the charge of the parasitic capacitance of the switch Q3 and regenerates to the input voltage Vin according to the path shown by (t4) in FIG. At this time, as shown by a period t4 in FIG. 2, when the source-drain voltage Vds of the switch Q3 decreases and becomes almost 0 V, the current IT flows through the diode through a path shown by (t5) in FIG. Turning on the switch Q3 at this timing enables ZVS. When the switch Q3 is turned on, a current flows from the input power supply in a direction to cancel the back electromotive force of the leakage inductance, gradually increases as shown by a period t6 in FIG. 3, and the leakage inductance 8 is completely reversed by the input voltage. When excited in the direction, a normal current for transmitting energy to the transformer secondary begins to flow as shown by a period t7 in FIG. Switches Q1 and Q4 operate in the same manner as switches Q2 and Q3.
[0033]
Referring to FIG. 4, when the load 9 is light, the inductance interposed between the switching circuit 3 and the primary winding of the transformer 4 is changed from the small inductance Ls2 (only the leakage inductance 8) to the large inductance Ls1 (the leakage inductance 8). The operation when switching to (the total inductance of the external inductance 10 and the external inductance 10) will be described. The horizontal axis in FIG. 4 indicates the magnitude of the load, and the vertical axis indicates the efficiency of the switching power supply. The area 13 is an area where the load 9 is light, the area 14 is an area where the load 9 is heavy, and 15 indicates a load point corresponding to the on / off switching of the external switch 11. Ls1 indicates a case where the inductance is large, and Ls2 indicates a case where the inductance is small. In the region 13 where the load 9 is light, the efficiency of the switching power supply increases with the increase in the load 9 regardless of the magnitude of the inductance. In this case, the efficiency of the switching power supply device is higher at the larger inductance Ls1. Therefore, when the load 9 is light, the efficiency of the switching power supply device can be increased by controlling the leakage inductance to a large value. On the other hand, in the region 14 where the load 9 is heavy, the efficiency decreases as the load 9 increases when the inductance Ls1 is large, and the efficiency increases as the load 9 increases when the inductance 9 is small. Therefore, when the load 9 is heavy, if the inductance interposed between the switching circuit 3 and the primary winding of the transformer 4 is controlled to be small, a decrease in the efficiency of the switching power supply device can be suppressed more than when the inductance is large. Become like
[0034]
For the sake of explanation, the operation when switching from the point A2 of the small inductance Ls2 to the point A1 of the large inductance Ls1 will be described. In this case, since the load 9 is in the light region 13, the inductance is switched from the small Ls2 to the large Ls1. Then, the changes in the waveforms of the switches Q2 and Q3 are as shown in FIG. Switching is performed at the timing when the gate pulse VG4 becomes high level. When the leakage inductance 8 is small as in the period t6 'in FIG. 5, ZVS cannot be performed because the source-drain voltage Vds of the switch Q3 does not drop to zero V. However, if the inductance is switched from small to large at the same time as the rise of the gate pulse VG4, a large energy is stored in the leakage inductance during the period t1, and the decrease in the current IT due to extracting the charge of the switch Q2 during the period t2 is reduced. , The charge of the switch Q3 can be extracted. As a result, as shown after switching of the leakage inductance in FIG. 5, the source-drain voltage Vds of the switch Q2 becomes 0 V before the rise of the gate pulse VG2, and the source-drain voltage Vds of the switch Q3 also becomes before the rise of the gate pulse VG3. , And ZVS is generated.
These operations are the same for the switches Q1 and Q4. Further, the switching timing of the inductance may be the moment when the gate pulse VG3 becomes a high level. In this case, the ZVS of the switches Q1 and Q3 is generated in the half cycle immediately after the switching, and the ZVS of the switches Q2 and Q3 is realized with a further delay of a half cycle.
[0035]
Next, when the load is heavy, the point is switched from the point B1 of the large leakage inductance Ls1 to the point B2 of the small leakage inductance Ls2 as shown in FIG. In this case, even if the inductance is small or large, the waveform is almost the same as that shown in FIG. The switching is performed at the same time as the rise of the gate pulse VG3 or VG4.
[0036]
FIG. 7 is a circuit diagram of a switching power supply according to another embodiment of the present invention, and portions corresponding to FIG. 1 are denoted by the same reference numerals. In this embodiment, a plurality of switching circuits 31 and 32 are provided in this example, and each of the switching circuits 31 and 32 includes a first arm (switches Q1 and Q2: switches Q5 and Q6) and the transformer 4. While the inductances Ls1 and Ls2 whose inductance values are different from each other exist between the primary arm and the primary winding, the second arms (switches Q3 and Q4) are shared with each other. When the load 9 is light, the control circuit 7 performs control so as to select the switching circuit 31 having the larger inductance, and to control the switching circuit 32 having the smaller inductance when the load is heavy.
[0037]
In the above-described embodiment, two large and small leakage inductances are used. However, a larger number of leakage inductances may be switched. For example, as shown in FIG. The two switching inductances Ls3 (large), Ls4 (medium), and Ls5 (small) are used, the first switching point is the intersection of the leakage inductances Ls3 (large) and Ls4 (middle), and the leakage point is the second switching point. This is the intersection of the inductances Ls4 (middle) and Ls5 (small). The efficiency of the entire switching power supply device may be improved by appropriately setting the intersection.
[0038]
【The invention's effect】
As described above, according to the present invention, when performing the zero volt switching operation using the excitation energy of the leakage inductance, even if the load is light, it is not necessary to increase the leakage inductance, and as a result, over the entire load area, In addition, the switching loss can be reduced, and the efficiency of the switching power supply can be improved accordingly.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a switching power supply device according to an embodiment of the present invention. FIG. 2 is a timing chart for explaining the operation of the switching power supply device of FIG. 1. FIG. 3 shows characteristics of a load and efficiency of the switching power supply device. FIG. 4 is a timing chart for explaining the operation of FIG. 1. FIG. 5 is a diagram showing a change in the voltage waveform of each part when the leakage inductance is switched from small to large under a light load. FIG. FIG. 7 is a diagram showing characteristics of efficiency and characteristics. FIG. 7 is a circuit diagram of a switching power supply according to another embodiment of the present invention. FIG. 8 is a load used for describing a switching power supply according to still another embodiment of the present invention. FIG. 9 is a diagram showing characteristics of the switching power supply and the efficiency of the switching power supply. FIG. 9 is a circuit diagram of a conventional switching power supply. FIG. Timing chart DESCRIPTION OF SYMBOLS
1 is an input power supply, 2 is an input capacitor, 3 is a switching circuit, 4 is a transformer, 5 is a rectifier circuit, 6 is a smoothing circuit, 7 is a control circuit, 8 is a leakage inductance, 9 is a load, 10 is an external inductance, 11 Is an external switch

Claims (4)

With a transformer,
A first and a second arm connected in parallel to an input power source, wherein each of the arms has a series configuration of switches on a high potential side and a low potential side, and a diode configured in parallel with each switch; A full-bridge type switching circuit including capacitances,
An inductance present in a current path between an interconnect of the high potential side and low potential side switches in one arm of the switching circuit and a primary winding of the transformer;
An output circuit provided on the secondary side of the transformer;
A control circuit that controls the operation timing of each switch of the switching circuit by a phase shift control method,
In a switching power supply device comprising:
A switching power supply device wherein the inductance is controlled to be large when the load is light, and the inductance is controlled to be small when the load is heavy. 2. The switching power supply device according to claim 1, wherein the control circuit detects a state of a load connected to the output circuit, and as a result of the detection, increases the inductance when the load is light and increases the inductance when the load is heavy. Is a switching power supply characterized in that the inductance is controlled to be small. 3. The switching power supply according to claim 1, wherein an inductor is connected to a current path between the switching circuit and a primary winding of the transformer, and an on / off switch is connected to the inductor in parallel. The circuit includes turning off the on / off switch to connect the inductor to the current path when the load is light, and electrically shorting the inductor by turning on the on / off switch when the load becomes heavy. Characteristic switching power supply. 3. The switching power supply device according to claim 1, further comprising at least two switching circuits, wherein each switching circuit has an inductance value between each first arm and a primary winding of the transformer. 4. While the inductances differing in magnitude are present, the respective second arms are shared with each other,
The switching power supply device, wherein the control circuit controls to select a switching circuit having a large inductance when the load is light, and to select a switching circuit having a small inductance when the load is heavy.

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