JP3748058B2 - Switching power supply - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an insulating type switching power supply apparatus that supplies DC power from an AC power supply to a load side via a bridge rectifier circuit, a transformer, and a switching element, and more specifically, improvement of input power factor and switching loss in the switching power supply apparatus. It is related to the reduction technology.
[0002]
[Prior art]
FIG. 5 is a circuit diagram showing a conventional technique of this type of one-stone type switching power supply device (also referred to as a flyback converter), and FIG. 6 is a waveform diagram for explaining the operation of FIG.
In FIG. 5, reference numeral 1 denotes an AC power supply, and a rectifier circuit 2 composed of a diode bridge is connected to both ends thereof. A reactor 3, a diode 9, a primary winding 11a of a transformer 11, and a switching element 8 are sequentially connected in series between the output terminal of the rectifier circuit 2 and a ground point. Connected in parallel.
[0003]
A capacitor 18 is connected between the anode of the diode 9 and one end of the switching element 8, and a capacitor 10 is connected between the cathode of the diode 9 and the ground point.
On the other hand, a diode 12 and a capacitor 13 are connected in series to the secondary winding 11 b of the transformer 11, and a load 14 is connected to both ends of the capacitor 13.
[0004]
The operation of this prior art will be described with reference to FIG. As a general operation, energy is stored in the primary winding 11a of the transformer 11 when the switching element 8 is turned on, and this energy is discharged from the secondary winding 11b of the transformer 11 when the switching element 8 is turned off. 14 performs a flyback operation for supplying a DC voltage.
[0005]
Hereinafter, the operation will be described focusing on the primary side of the transformer 11.
First, at the same time when the switching element 8 at time T ₁ of the FIG 6 is turned on, the discharge current of the capacitor 18 flows through the switching element 8, come fall voltage of the switching element 8. For this reason, the power of the hatched portion shown in FIG. 6 becomes a switching loss when the switching element 8 is turned on.
[0006]
During the period from T _{1 to} T _{2 when} the switching element 8 is on, the energy of the capacitor 18 is stored in the reactor 3 through a path of the capacitor 18 → the switching element 8 → the rectifier circuit 2 (and the AC power supply 1) → the reactor 3. In this current path, there is an AC power source 1, and even when the voltage of the capacitor 18 is lower than the AC power source voltage, the diode of the rectifier circuit 2 conducts, so the conduction angle of the diode of the rectifier circuit 2 widens and the power factor is improved. The
[0007]
At the same time, the switching element 8 stores energy in the primary winding 11 a of the transformer 11 during the period of T _{1 to} T ₂ . When the switching element 8 is turned off at time T _2, the voltage generated in the secondary winding 11b of the transformer 11 which charges the capacitor 13, the capacitor 18 is charged by the voltage generated in the primary winding 11a. For this reason, the voltage of the switching element 8 rises as shown in FIG. 6 and then becomes a constant value.
[0008]
In the period from T _{2 to} T ₃ , the energy stored in the reactor 3 is transferred to the capacitor 10 through the path of the reactor 3 → the diode 9 → the capacitor 10 → the rectifier circuit 2. There is also an AC power source 1 in this current path, and even when the voltage of the capacitor 10 is lower than the AC power source voltage, the diode of the rectifier circuit 2 conducts, so the conduction angle of the diode of the rectifier circuit 2 widens and the power factor is improved. .
[0009]
When the current of reactor 3 becomes zero at time T ₃ , the voltage of switching element 8 decreases while oscillating due to series resonance by capacitor 18, primary winding 11 a and capacitor 10, and then switching element 8 is turned on again at time T ₄ . When turned on, to repeat the operation similar to the time T ₁ after the above-mentioned.
[0010]
[Problems to be solved by the invention]
In the conventional technique described above, the switching element 8 at time T ₁ and T ₄ there is a problem that the switching loss is large when turned on.
Therefore, the present invention intends to provide a switching power supply apparatus that can improve the input power factor while reducing the switching loss of the switching element 8.
[0011]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention according to claim 1 rectifies an AC power source into a one-way current via a bridge rectifier circuit, and a current direction between an output terminal of the bridge rectifier circuit and a grounding point. A first diode, a primary winding of the first transformer, and a main switching element are sequentially connected in series, and a first capacitor is connected in parallel to the series circuit of the primary winding and the main switching element. In the switching power supply device connected and configured to output a DC voltage from the secondary winding of the first transformer by turning on and off the main switching element,
Connect a snubber capacitor and freewheeling diode in parallel to the main switching element,
A primary winding of a second transformer is connected in series between the output terminal of the bridge rectifier circuit and the first diode, and a connection point between the first diode and the primary winding of the second transformer; A second capacitor, a reactor, and an auxiliary switching element are sequentially connected in series with the ground point; and
Between the connection point between the primary winding of the first transformer and the main switching element and the connection point between the second capacitor and the reactor, the second diode and the second voltage transformer along the flow direction. The secondary winding of the instrument is connected in series sequentially,
In order to discharge the electric charge of the snubber capacitor, the auxiliary switching element is turned on before the main switching element is turned on, and is turned off before the main switching element is turned off.
[0012]
According to a second aspect of the present invention, the AC power source is rectified into a one-way current via a bridge rectifier circuit, and the first diode is provided along the flow direction between the output terminal of the bridge rectifier circuit and the ground point. And the primary winding of the first transformer and the main switching element are sequentially connected in series, and a first capacitor is connected in parallel to the series circuit of the primary winding and the main switching element. In the switching power supply unit configured to output a DC voltage from the secondary winding of the first transformer by turning on and off,
Connect a snubber capacitor and freewheeling diode in parallel to the main switching element,
A primary winding of a second transformer is connected in series between the output terminal of the bridge rectifier circuit and the first diode, and a connection point between the first diode and the primary winding of the second transformer; A third diode, a reactor, and an auxiliary switching element are sequentially connected in series along the flow direction between the ground point and the ground point; and
Between the connection point between the primary winding of the first transformer and the main switching element and the connection point between the third diode and the reactor, the second diode and the second voltage transformer along the flow direction. The secondary winding of the instrument is connected in series sequentially,
In order to discharge the electric charge of the snubber capacitor, the auxiliary switching element is turned on before the main switching element is turned on, and is turned off before the main switching element is turned off.
[0013]
The invention according to claim 3 is the switching power supply device according to claim 1 or 2, wherein the on-period of the auxiliary switching element is a fixed time.
[0014]
According to a fourth aspect of the present invention, in the switching power supply device according to the first or second aspect, the auxiliary switching element is turned off a predetermined period before the timing at which the main switching element is turned off, and the on period of the auxiliary switching element is set to It is variable according to the timing at which the main switching element is turned off.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a circuit diagram showing a first embodiment of the present invention. The same components as those in FIG. 5 are denoted by the same reference numerals and description thereof will be omitted. Hereinafter, different parts will be mainly described. This embodiment corresponds to the invention of claim 1.
[0016]
In FIG. 1, reference numeral 17 denotes a second transformer having a primary winding 17 a and a secondary winding 17 b, and the primary winding 17 a is connected between the output terminal of the rectifier circuit 2 and the anode of the diode 9. Yes. Similarly to FIG. 5, one end of a capacitor 18 is connected to the anode of the diode 9.
A reactor 19 and the auxiliary switching element 6 are connected in series between the other end of the capacitor 18 and the grounding point.
[0017]
Between the connection point between the primary winding 11a of the first transformer 11 and the main switching element 8 and the other end of the capacitor 18, the diode 5 and the secondary winding 17b of the second transformer 17 Are connected in series.
A snubber capacitor 7 is connected in parallel to the main switching element 8 together with the diode 16, and a diode 15 is connected in parallel to the auxiliary switching element 6.
[0018]
In the above configuration, the diode 9 corresponds to the first diode in claim 1, the diode 5 corresponds to the second diode, the capacitor 10 corresponds to the first capacitor, and the capacitor 18 corresponds to the second capacitor. Yes.
[0019]
Here, the first transformer 11, the main switching element 8, the diode 12, the capacitor 13 and the load 14 perform a flyback power supply operation as in the prior art, and the main switching element 8 is turned on and off by the first transformer. 11 primary side energy is supplied to the load 14 from the secondary side.
The auxiliary switching element 6 operates to reduce the switching loss of the main switching element 8 and improve the input power factor of the switching power supply device.
[0020]
The detailed operation of this embodiment will be described below with reference to FIG. In FIG. 2, the waveform shown by the solid line is the operation waveform of the present embodiment.
[0021]
In the period T ₁ through T ₂ in FIG. 2, with the turning on the auxiliary switching element 6 at the time of the previous T ₁ than the main switching element 8 is turned on, the main switching element 8 and the auxiliary switching element 6 is off The electric charge stored in the snubber capacitor 7 until then is discharged through the path of the diode 5 → the secondary winding 17 b of the second transformer 17 → the reactor 19 → the auxiliary switching element 6, and is stored as excitation energy in the reactor 19. . This discharge, the voltage of the main switching element 8 when turning on the main switching element 8 to time T _2, after which will be described later is zero, the switching loss is reduced thereby enabling zero-voltage switching.
Incidentally, on the same time the voltage of the main switching element 8 by the discharging of the auxiliary switching element 6 is gradually falls, the time T _2, after which the snubber capacitor 7 becomes zero voltage and turns on the main switching element 8.
[0022]
Further, the discharge current of the snubber capacitor 7 described above is a series resonance current between the reactor 19 and the snubber capacitor 7, and the change in this current is moderated by the reactor 19, so that the auxiliary switching element 6 is turned on by soft switching (so-called zero). Current switching) and switching loss is reduced.
That is, when the auxiliary switching element 6 is turned on, a voltage is generated in the reactor 19 in a direction opposite to the discharge current of the snubber capacitor 7, so that the increase in the discharge current is moderated and soft switching (zero current switching) is achieved. Is.
[0023]
The capacitor 18 becomes positive on the side of the reactor 19 by the primary winding 11a of the first transformer 11 and the secondary winding 17b of the second transformer 17 when both the main switching element 8 and the auxiliary switching element 6 are off. When the auxiliary switching element 6 is turned on, the capacitor 18 is discharged along the path of the reactor 19 → the auxiliary switching element 6 → the rectifier circuit 2 → the primary winding 17 a of the second transformer 17. The energy of the capacitor 18 is accumulated in the primary winding 17a.
[0024]
Next, in the period T _{2 to} T ₃ , the main switching element 8 is turned on after the voltage of the snubber capacitor 7 drops to zero voltage at time T ₂ . The auxiliary switching element 6 shall be allowed to turn on until time T _3.
The excitation energy accumulated in the reactor 19 in the period T _{1 to} T ₂ is the path of the secondary winding 17 b of the second transformer 17 using the reactor 19 as a power source, the reactor 19 → the auxiliary switching element 6 → the diode 16 → the diode 5 →. Is discharged by the current flowing through the auxiliary switching element 6, and the current of the auxiliary switching element 6 decreases. Here, the diode 16 serves as a so-called freewheeling diode.
[0025]
Due to the current flowing through the secondary winding 17b, the primary winding 17a is induced according to the ampere-turn rule, and the reactor 19 → the auxiliary switching element 6 → the rectifier circuit 2 → the primary winding 17a of the second transformer 17 → the capacitor 18 It is discharged along the route and regenerated on the AC power supply 1 side. When the discharge is completed, a current flows through the path of the primary winding 17a of the second transformer 17 → the capacitor 18 → the reactor 19 → the auxiliary switching element 6 → the rectifier circuit 2, and the reactor 19 is subjected to static electricity as excitation energy. Stored as electric energy. Since there is an AC power source 1 in this current path, the conduction angle of the rectifier circuit 2 is widened and the power factor is improved.
[0026]
Next, in the period T _{3 to} T ₄ , when the auxiliary switching element 6 is turned off at the time T ₃ , the auxiliary switching element 6 includes the AC power supply voltage, the voltage of the primary winding 17 a of the second transformer 17, and the capacitor 18. A sum with voltage is applied. During this period, the excitation energy stored in the reactor 19 and the electrostatic energy stored in the capacitor 18 are discharged through the path of the diode 9 → the capacitor 10 → the rectifier circuit 2 to boost the voltage of the capacitor 10. By this boosting operation, the voltage of the capacitor 10 can be made higher than the peak value of the AC power supply voltage, the effective current flowing during the ON period of the main switching element 8 can be reduced, and the conduction loss of the main switching element 8 can be reduced. .
[0027]
Further, since there is an AC power source 1 in this current path, even when the voltage of the capacitor 10 is lower than the voltage of the AC power source 1, the diode of the rectifier circuit 2 conducts, so that the conduction angle of the rectifier circuit 2 is widened and the power factor is improved. Is done. When this discharge is finished, the voltage of the capacitor 10 is applied to the auxiliary switching element 6.
[0028]
In the period T _{4 to} T ₆ , when the main switching element 8 is turned off at time T ₄ , the snubber capacitor 7 is charged, and the voltage applied to the main switching element 8 gradually increases. The off time is zero voltage switching. Further, the capacitor 18 and the exciting inductance of the primary winding 11a along the path of the diode 9 → the primary winding 11a of the first transformer 11 → the diode 5 → the secondary winding 17b of the second transformer 17 Series resonance current due to. The current is stopped by being reversely blocked by the diodes 9 and 5, and thereafter, when the current of the diode 12 finishes flowing, series resonance is started by the capacitor 7 and the exciting inductance of the primary winding 11 a of the first transformer 11. The current flows through the path of the capacitor 7 → the primary winding 11 a → the capacitor 10.
At time T ₅ after the current of the diode 12 becomes zero start voltage of the main switching element 8 and the auxiliary switching element 6 is vibrating, then by turning on the auxiliary switching element 6 at time T _6, the time T ₁ after Repeat the operation.
[0029]
Next, FIG. 3 is a circuit diagram showing a second embodiment of the present invention. This embodiment corresponds to the invention of claim 2 and has the same configuration as that in FIG. 1 except that a diode 20 is connected instead of the capacitor 18 in FIG.
Here, the diode 20 corresponds to a third diode in claim 2.
[0030]
Hereinafter, the operation of the present embodiment will be described with reference to FIG. In this embodiment, the voltage waveform of the auxiliary switching element 6 in FIG. 2 and a part of the current waveform of the diode 12 are shown by dotted lines, and the other operation waveforms are the same as those in the first embodiment (the solid line in FIG. 2). Waveform). Of course, in the present embodiment, there is nothing corresponding to the current waveform of the capacitor 18.
[0031]
Since the operations in the periods T _{1 to} T ₃ are the same as those in the first embodiment, the other periods will be described below.
When the auxiliary switching element 6 is turned off during the periods T _{3 to} T ₄ , the sum of the AC power supply voltage and the voltage of the primary winding 17 a of the second transformer 17 is applied to the switching element 6. The exciting energy stored in the primary winding 17a of the time T ₃ before the second transformer 17 is released by the current flowing through the path of the diode 9 → capacitor 10 → rectifier circuit 2, boosts the voltage of the capacitor 10 To do.
At this time, the voltage of the auxiliary switching element 6 is reduced by the amount of energy stored in the capacitor 18 of FIG. 1 as compared with the solid line of the first embodiment, as indicated by the dotted line. Since the AC power supply 1 is present in the current path, the conduction angle of the diode of the rectifier circuit 2 is widened, and the input power factor is improved.
When the excitation energy stored in the primary winding 17a is released, the voltage of the capacitor 10 is applied to the auxiliary switching element 6.
[0032]
In the period T _{4 to} T ₅ , when the main switching element 8 is turned off, the snubber capacitor 7 is charged, and the voltage applied to the main switching element 8 gradually rises. Therefore, when the main switching element 6 is turned off, zero voltage switching is performed. It is.
Thereafter, when the current of the diode 12 finishes the flow at time T _5, the series resonance starts by the exciting inductance of the primary winding 11a of the capacitor 7 and the first transformer 11, the capacitor 7 → primary winding 11a → capacitor 10 A current flows through the path, and the voltages of the main switching element 8 and the auxiliary switching element 6 start to oscillate.
Further, by turning on the auxiliary switching element 6 at time T _6, to repeat the time T ₁ after the operation.
[0033]
Note that the voltage waveform of the auxiliary switching element 6 and the current waveform of the diode 12 after the time T ₄ are different between the first and second embodiments in the series of the primary winding 11 a of the first transformer 11 and the capacitor 18. This is due to the presence or absence of resonance current.
[0034]
Further, in the first and second embodiments described above, by fixing the ON period (period T _{1 to} T ₃ in FIG. 2) of the auxiliary switching element 6, the primary winding 17 a of the second transformer 17 is used. The boost value of the voltage of the capacitor 10 with respect to the AC power supply voltage peak value can be set to a value proportional to the AC power supply voltage.
Thus, setting the ON period of the auxiliary switching element 6 as a fixed period corresponds to an embodiment of the invention of claim 3 (a third embodiment of the invention).
The relationship between the AC power supply voltage and the boosted value of the capacitor 10 is shown by a solid line in FIG.
[0035]
Further, the auxiliary switching element 6 is turned off a predetermined period before the timing at which the main switching element 8 is turned off, and the on period of the auxiliary switching element 6 is made variable according to the off timing of the main switching element 8, so that FIG. As shown by the dotted line, the difference in the boost value between when the AC power supply voltage is low and when it is high can be reduced.
[0036]
That is, even when the off timing of the main switching element 8 changes, the period T _{3 to} T ₄ in FIG. 2 is always constant, so that when the AC power supply voltage is low, the boosting rate of the capacitor 10 is relatively large. When the AC power supply voltage is high, the boosting rate of the capacitor 10 is relatively reduced. As a result, the effective current of the main switching element 8 can be significantly reduced, and when the AC power supply voltage is high, the boosting rate is small, so that an inexpensive capacitor with a low withstand voltage can be used.
In addition, said matter is corresponded to embodiment (4th Embodiment of this invention) of invention of Claim 4.
[0037]
【The invention's effect】
As described above, according to the present invention, in an insulating switching power supply device, it is possible to improve the input power factor while reducing switching loss, and to provide a switching power supply device with lower loss and higher efficiency than the conventional one. be able to.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a first embodiment of the present invention.
FIG. 2 is a waveform diagram showing the operation of the first and second embodiments of the present invention.
FIG. 3 is a circuit diagram showing a second embodiment of the present invention.
FIG. 4 is an operation explanatory diagram of third and fourth embodiments of the present invention.
FIG. 5 is a circuit diagram showing a conventional technique.
FIG. 6 is a waveform diagram showing the operation of the prior art.
[Explanation of symbols]
1 AC power supply 2 Rectifier circuit 5, 9, 12, 15, 16, 20 Diode 6, 8 Switching element 7, 10, 13, 18 Capacitor 11, 17 Transformer 11a, 17a Primary winding 11b, 17b Secondary winding 14 Load 19 reactor

Claims (4)

The AC power source is rectified into a one-way current through a bridge rectifier circuit, and a primary diode and a first transformer primary are provided along the flow direction between the output terminal of the bridge rectifier circuit and a ground point. The winding and the main switching element are sequentially connected in series, and a first capacitor is connected in parallel to the series circuit of the primary winding and the main switching element. In a switching power supply device that outputs a DC voltage from the secondary winding,
Connect a snubber capacitor and freewheeling diode in parallel to the main switching element,
A primary winding of a second transformer is connected in series between the output terminal of the bridge rectifier circuit and the first diode, and a connection point between the first diode and the primary winding of the second transformer; A second capacitor, a reactor, and an auxiliary switching element are sequentially connected in series with the ground point; and
Between the connection point between the primary winding of the first transformer and the main switching element and the connection point between the second capacitor and the reactor, the second diode and the second voltage transformer along the flow direction. The secondary winding of the instrument is connected in series sequentially,
In order to discharge the electric charge of the snubber capacitor, the auxiliary switching element is turned on before the main switching element is turned on, and is turned off before the main switching element is turned off. The AC power source is rectified into a one-way current through a bridge rectifier circuit, and a primary diode and a first transformer primary are provided along the flow direction between the output terminal of the bridge rectifier circuit and a ground point. The winding and the main switching element are sequentially connected in series, and a first capacitor is connected in parallel to the series circuit of the primary winding and the main switching element, and the first transformer is turned on and off by the main switching element. In a switching power supply device that outputs a DC voltage from the secondary winding,
Connect a snubber capacitor and freewheeling diode in parallel to the main switching element,
A primary winding of a second transformer is connected in series between the output terminal of the bridge rectifier circuit and the first diode, and a connection point between the first diode and the primary winding of the second transformer; A third diode, a reactor, and an auxiliary switching element are sequentially connected in series along the flow direction between the ground point and the ground point; and
Between the connection point between the primary winding of the first transformer and the main switching element and the connection point between the third diode and the reactor, the second diode and the second voltage transformer along the flow direction. The secondary winding of the instrument is connected in series sequentially,
In order to discharge the electric charge of the snubber capacitor, the auxiliary switching element is turned on before the main switching element is turned on, and is turned off before the main switching element is turned off. The switching power supply device according to claim 1 or 2,
A switching power supply device characterized in that the ON period of the auxiliary switching element is a fixed time. The switching power supply device according to claim 1 or 2,
A switching power supply characterized in that the auxiliary switching element is turned off for a predetermined period before the timing at which the main switching element is turned off, and the on period of the auxiliary switching element is made variable according to the timing at which the main switching element is turned off. apparatus.

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