JP4419341B2 - Switching power supply - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a switching power supply device, and more particularly to a half-bridge type switching power supply device.
[0002]
[Prior art]
Conventionally, what is called a DC / DC converter is known as a switching power supply device. A typical DC / DC converter converts a DC input to AC once using a switching circuit, then transforms it (steps up or down) using a transformer, and further converts it to DC using an output circuit. Thus, a DC output having a voltage different from the input voltage can be obtained.
[0003]
FIG. 4 is a circuit diagram showing a conventional switching power supply device of this type.
[0004]
As shown in FIG. 4, the conventional switching power supply apparatus includes a transformer 1, a half bridge circuit 2 provided on the primary side of the transformer 1, a rectifier circuit 3 provided on the secondary side of the transformer 1, The output voltage Vo is monitored via the smoothing circuit 4 provided in the subsequent stage of the rectifier circuit 3 and the insulating circuit 5, and based on this, the first and second main switches 6 and 7 included in the half bridge circuit 2 are turned on. Control circuit 8 for controlling / off. The half bridge circuit 2 is connected in series between both ends of the input power source 9 and the first input capacitor 10 connected between both ends of the input power source 9 in addition to the first and second main switches 6 and 7. The second and third input capacitors 11 and 12 are provided. Between the nodes of the first and second main switches 6 and 7 and the nodes of the second and third input capacitors 11 and 12, the transformer 1 A primary winding N1 is connected. The rectifier circuit 3 includes first and second diodes 13 and 14, and the smoothing circuit 4 includes a smoothing inductor 15 and a smoothing capacitor 16. The rectifier circuit 3 and the smoothing circuit 4 constitute an output circuit.
[0005]
Further, in this type of switching power supply device, as shown in FIG. 4, a leakage inductance 17 is provided between the node of the second and third input capacitors 11 and 12 and the primary winding N1 of the transformer 1. Existing. The leakage inductance 17 is a parasitic inductance component.
[0006]
In such a configuration, the first and second main switches 6 and 7 are alternately turned on with a predetermined dead time under the control of the control circuit 8, whereby the input voltage Vin and the transformer 1 are switched. An output voltage Vo determined by the turns ratio is applied to the load 18.
[0007]
FIG. 5 is a timing chart showing the operation of the conventional switching power supply device. In FIG. 5, Vds1 means the voltage across the first main switch 6 (between the source and drain), Id1 means the current flowing through the first main switch 6, and Vds2 means the first 2 means a voltage between both ends of the main switch 7 (between source and drain), Id2 means a current flowing through the second main switch 7, and Vgs1 means a gate voltage of the first main switch 6. Vgs2 means the gate voltage of the second main switch 7. T1 means a secondary side voltage of the transformer 1, and D1 means a current flowing through the first diode 13.
[0008]
As shown in FIG. 5, in the conventional switching power supply device, when the first main switch 6 is turned off (time t0), the voltage Vds1 between both ends of the first main switch 6 is about 0V from the state of about 0V. While rapidly increasing to 1/2 Vin, the current Id1 flowing through the first main switch 6 rapidly decreases to 0A. Thereafter, when the second main switch 7 is turned on with a predetermined dead time (time t1), the voltage Vds2 between both ends of the second main switch 7 is fixed to almost 0 V, and the second main switch 7 The current Id2 flowing through 7 rises relatively slowly due to the presence of the leakage inductance 17.
[0009]
Although not shown in FIG. 5, even when the second main switch 7 is turned off, the voltage Vds2 across the second main switch 7 is rapidly increased from approximately 0V to approximately 1 / 2Vin. Current Id2 flowing through the second main switch 7 rapidly decreases to 0A. Thereafter, when the first main switch 6 is turned on with a predetermined dead time interposed therebetween, the voltage Vds1 between both ends of the first main switch 6 is fixed to approximately 0 V, and the current flowing through the first main switch 6 Id1 rises relatively slowly due to the presence of the leakage inductance 17.
[0010]
As described above, in the conventional switching power supply device, due to the presence of the leakage inductance 17, the increase in the current Id1 and the current Id2 when the first main switch 6 and the second main switch 7 are turned on becomes relatively gradual. Thereby, the switching loss at the time of turn-on of the 1st main switch 6 or the 2nd main switch 7 is reduced.
[0011]
[Problems to be solved by the invention]
However, as shown in FIG. 5, in the conventional switching power supply device, when the first main switch 6 is turned off, the increase in the voltage Vds1 and the decrease in the current Id1 occur almost simultaneously, so the voltage Vds1 and the current Id1 A large switching loss occurs in the overlapping portion. This problem is the same when the second main switch 7 is turned off, and a large switching loss occurs in the overlapping portion of the voltage Vds2 and the current Id2.
[0012]
Accordingly, an object of the present invention is to provide a switching power supply device in which switching loss at turn-off is reduced.
[0013]
[Means for Solving the Problems]
An object of the present invention is to provide a transformer, a half bridge circuit provided on the primary side of the transformer, an output circuit provided on the secondary side of the transformer, and a control circuit for controlling the operation of the half bridge circuit. The half-bridge circuit includes first and second main switches connected in series between input power sources, a resonance circuit, and a node of the first and second main switches. And an auxiliary switch provided between the resonance circuit and the control circuit, wherein the control circuit turns on the auxiliary switch for a certain period including when the first main switch is turned off, and the second main switch. the switching power supply apparatus characterized by turning on the auxiliary switch at a fixed period including the time of turn-off It is made.
[0014]
According to the present invention, since the resonance current can flow through the resonance circuit by controlling the auxiliary switch, the current flowing through the first and second main switches immediately before the turn-off can be reduced using the resonance current. Can do. As a result, it is possible to significantly reduce the switching loss when the first and second main switches are turned off.
[0015]
In a preferred embodiment of the present invention, the resonant circuit comprises a series circuit including an inductor and a capacitor.
[0017]
In a further preferred aspect of the present invention, the control circuit turns off the first main switch at a timing when the current flowing through the first main switch decreases after turning on the auxiliary switch, After the auxiliary switch is turned on, the second main switch is turned off at a timing when the current flowing through the second main switch decreases.
[0018]
In a further preferred aspect of the present invention, the control circuit turns off the auxiliary switch and turns off the auxiliary switch before turning on the second main switch after turning off the first main switch. After the switch is turned off, the auxiliary switch is turned off before the first main switch is turned on.
[0019]
In a further preferred aspect of the present invention, the control circuit turns off the auxiliary switch at a timing when a resonance current flowing through the resonance circuit becomes substantially zero.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0021]
FIG. 1 is a circuit diagram showing a switching power supply device 20 according to a preferred embodiment of the present invention.
[0022]
As shown in FIG. 1, the switching power supply device 20 according to this embodiment includes a transformer 21, a half bridge circuit 22 provided on the primary side of the transformer 21, and a rectification provided on the secondary side of the transformer 21. The output voltage Vo is monitored via the circuit 23, the smoothing circuit 24 provided in the subsequent stage of the rectifier circuit 23, and the insulating circuit 25, and based on this, the first and second main switches 26 included in the half bridge circuit 22 are monitored. , 27 and a control circuit 29 for controlling on / off of the auxiliary switch 28.
[0023]
The half bridge circuit 22 includes a first input capacitor 31 connected between both ends of the input power supply 30 in addition to the first and second main switches 26 and 27 and the auxiliary switch 28, and a series connection between both ends of the input power supply 30. And second and third input capacitors 32, 33 connected to each other, between the nodes of the first and second main switches 26, 27 and the nodes of the second and third input capacitors 32, 33. The primary winding N1 of the transformer 21 is connected. Further, the half bridge circuit 22 has a resonance circuit composed of an inductor 34 and a capacitor 35, one end of which is connected to the lower electrode of the input power supply 30, and the other end of the resonance circuit is connected via an auxiliary switch 28. The first and second main switches 26 and 27 are connected to the nodes.
[0024]
The rectifier circuit 23 includes first and second diodes 36 and 37, and the smoothing circuit 24 includes a smoothing inductor 38 and a smoothing capacitor 39. The rectifier circuit 23 and the smoothing circuit 24 constitute an output circuit.
[0025]
Also in the switching power supply device 20 according to the present embodiment, as shown in FIG. 1, there is a parasitic between the node of the second and third input capacitors 32 and 33 and the primary winding N1 of the transformer 21. There is a leakage inductance 40 that is an inductance component.
[0026]
In such a configuration, the first and second main switches 26 and 27 are alternately turned on with a predetermined dead time under the control of the control circuit 29, whereby the input voltage Vin and the transformer 1 are switched. An output voltage Vo determined by the turns ratio is applied to the load 41.
[0027]
Next, the operation of the switching power supply device 20 according to this embodiment will be described.
[0028]
FIG. 2 is a timing chart showing an operation when the main switch that is turned on is switched from the first main switch 26 to the second main switch 27 in the switching power supply device 20 according to the present embodiment. In FIG. 2 (the same applies to FIG. 3 described below), Vds1 means a voltage across the first main switch 26 (between the source and drain), and Id1 means the first main switch 26. Vds2 means the voltage across the second main switch 27 (between source and drain), Id2 means the current flowing through the second main switch 27, and Vgs1 The gate voltage of the first main switch 26 is meant, Vgs2 means the gate voltage of the second main switch 27, and Vgs3 means the gate voltage of the auxiliary switch 28. T1 means the secondary side voltage of the transformer 21.
[0029]
As shown in FIG. 2, in the switching power supply device 20 according to the present embodiment, when the main switch that is turned on is switched from the first main switch 26 to the second main switch 27, the first main switch 26. First, the auxiliary switch 28 is turned on (time t10). Accordingly, a resonance current flows through the resonance circuit including the inductor 34 and the capacitor 35 via the first main switch 26 and the auxiliary switch 28. With this resonance current, the current Id1 flowing through the first main switch 26 increases once but then decreases, and the amount of current approaches 0A.
[0030]
Then, at the timing when the current Id1 flowing through the first main switch 26 is sufficiently reduced, the first main switch 26 is turned off (time t11). As a result, the voltage Vds1 across the first main switch 26 rises rapidly from the substantially 0V state to about 1 / 2Vin, but at the timing when the first main switch 26 turns off, Since the current Id1 flowing through the switch 26 has already been sufficiently reduced, the switching loss is greatly reduced as compared with the conventional switching power supply device.
[0031]
Next, the auxiliary switch 28 is turned off at the timing when the resonance current flowing through the resonance circuit including the inductor 34 and the capacitor 35 becomes approximately 0 A (time t12). Thereby, the switching loss accompanying the turn-off of the auxiliary switch 28 hardly occurs.
[0032]
Then, after a predetermined dead time has elapsed from time t11, the second main switch 27 is turned on (time t13). As a result, the voltage Vds2 across the second main switch 27 is fixed to approximately 0 V, and the current Id2 flowing through the second main switch 27 rises relatively gently due to the presence of the leakage inductance 40.
[0033]
From the above, it can be seen that the switching loss accompanying the turn-off (time t11) of the first main switch 26 is greatly reduced.
[0034]
FIG. 3 is a timing chart showing an operation when the main switch to be turned on is switched from the second main switch 27 to the first main switch 26 in the switching power supply device 20 according to the present embodiment.
[0035]
As shown in FIG. 3, in the switching power supply device 20 according to the present embodiment, when the main switch that is turned on is switched from the second main switch 27 to the first main switch 26, the second main switch 27. First, the auxiliary switch 28 is turned on (time t20). Thus, a resonance current flows through the resonance circuit including the inductor 34 and the capacitor 35 via the second main switch 27 and the auxiliary switch 28. With this resonance current, the current Id2 flowing through the second main switch 27 decreases, and the amount of current approaches 0A.
[0036]
Then, at the timing when the current Id2 flowing through the second main switch 27 is sufficiently reduced, the second main switch 27 is turned off (time t21). As a result, the voltage Vds2 across the second main switch 27 rises rapidly from the substantially 0 V state to about 1/2 Vin, but at the timing when the second main switch 27 is turned off, the second main switch 27 is turned off. Since the current Id2 flowing through the switch 27 has already been sufficiently reduced, the switching loss is greatly reduced as compared with the conventional switching power supply device.
[0037]
Next, the auxiliary switch 28 is turned off at the timing when the resonance current flowing through the resonance circuit including the inductor 34 and the capacitor 35 becomes approximately 0 A (time t22). Thereby, the switching loss accompanying the turn-off of the auxiliary switch 28 hardly occurs.
[0038]
Then, after a predetermined dead time has elapsed from time t21, the first main switch 26 is turned on (time t23). As a result, the voltage Vds1 across the first main switch 26 is fixed to approximately 0 V, and the current Id1 flowing through the first main switch 26 rises relatively gently due to the presence of the leakage inductance 40.
[0039]
From the above, it can be seen that the switching loss accompanying the turn-off (time t21) of the second main switch 27 is greatly reduced.
[0040]
As described above, in the switching power supply device 20 according to this embodiment, the switching loss due to the turn-off of the first and second main switches 26 and 27 is caused by the action of the resonance circuit including the auxiliary switch 28 and the inductor 34 and the capacitor 35. Since it is greatly reduced, highly efficient power conversion can be performed.
[0041]
Note that the timing at which the auxiliary switch 28 is turned on (time t10, time t20) and the timing at which the auxiliary switch 28 is turned off (time t12, time t22) depend on the constant of the resonance circuit including the inductor 34 and the capacitor 35. However, due to the resonance current, the current Id1 that flows through the first main switch 26 or the second main switch 27 flows at the timing (time t11, time t21) when the first main switch 26 or the second main switch 27 is turned off. It is preferable to turn on the auxiliary switch 28 at a timing when the current Id2 becomes as small as possible and to turn off the auxiliary switch 28 at a timing when the resonance current becomes approximately 0A.
[0042]
The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the invention described in the claims, and these are also included in the scope of the present invention. Needless to say.
[0043]
That is, the present invention can also be applied to a switching power supply device having a circuit configuration different from that of the switching power supply device 20 shown in the above embodiment as long as it is a half-bridge type switching power supply device. For example, in the switching power supply device 20 according to the above-described embodiment, the rectifier circuit including the first and second diodes 36 and 37 is used as the rectifier circuit 23, but a synchronous rectifier type rectifier circuit using transistors is used. It doesn't matter.
[0044]
【The invention's effect】
As described above, according to the present invention, there is provided a switching power supply device that can reduce switching loss at the time of turn-off and thereby perform highly efficient power conversion.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a switching power supply device 20 according to a preferred embodiment of the present invention.
FIG. 2 is a timing chart showing an operation when the main switch that is turned on in the switching power supply device 20 is switched from the first main switch 26 to the second main switch 27;
FIG. 3 is a timing chart showing an operation when the main switch that is turned on in the switching power supply device 20 is switched from the second main switch 27 to the first main switch 26;
FIG. 4 is a circuit diagram showing a conventional switching power supply device.
FIG. 5 is a timing chart showing an operation of a conventional switching power supply device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Transformer 2 Half bridge circuit 3 Rectifier circuit 4 Smoothing circuit 5 Insulation circuit 6 1st main switch 7 2nd main switch 8 Control circuit 9 Input power supply 10 1st input capacitor 11 2nd input capacitor 12 3rd input Capacitor 13 First diode 14 Second diode 15 Smoothing inductor 16 Smoothing capacitor 17 Leakage inductance 18 Load 20 Switching power supply device 21 Transformer 22 Half bridge circuit 23 Rectifier circuit 24 Smoothing circuit 25 Insulating circuit 26 First main switch 27 Second main switch 28 Auxiliary switch 29 Control circuit 30 Input power supply 31 First input capacitor 32 Second input capacitor 33 Third input capacitor 34 Inductor 35 Capacitor 36 First diode 37 Second diode 38 Smoothing Inductor 39 smoothing capacitor 40 leakage inductance 41 load

Claims (5)

A switching power supply device comprising a transformer, a half bridge circuit provided on the primary side of the transformer, an output circuit provided on the secondary side of the transformer, and a control circuit for controlling the operation of the half bridge circuit. The half-bridge circuit is connected between the first and second main switches connected in series between the input power sources, the resonance circuit, the node of the first and second main switches, and the resonance circuit. And the control circuit turns on the auxiliary switch for a certain period including when the first main switch is turned off, and includes a certain period including when the second main switch is turned off. The switching power supply device according to claim 1 , wherein the auxiliary switch is turned on .   The switching power supply device according to claim 1, wherein the resonance circuit includes a series circuit including an inductor and a capacitor. The control circuit turns off the auxiliary switch, turns off the first main switch at a timing when the current flowing through the first main switch decreases, turns on the auxiliary switch, and then turns on the first switch. 3. The switching power supply device according to claim 1 , wherein the second main switch is turned off at a timing when a current flowing through the two main switches decreases. The control circuit turns off the auxiliary switch before turning on the second main switch after turning off the first main switch and turning off the second main switch and turning off the second main switch. 4. The switching power supply device according to claim 1 , wherein the auxiliary switch is turned off before the switch is turned on. 5. 5. The switching power supply device according to claim 4 , wherein the control circuit turns off the auxiliary switch at a timing when a resonance current flowing through the resonance circuit becomes substantially zero.

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