JP4348472B2 - 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 technique for making a switching operation of a switch element into a soft switch using a resonance action.
[0002]
[Prior art]
FIG. 4 is a circuit diagram showing an example of a conventional system, which is already known as switching using resonance action (basic of Corona switching converter). In FIG. 4, current flows through the primary winding 7 a of the transformer during the ON period of the switch element 8, most of which is supplied to the load 15 via the secondary winding 7 b, and part of the excitation energy is supplied to the transformer 7. Accumulated as. When the switch element 8 is turned off from the ON state, the excitation energy of the transformer 7 flows through a closed circuit formed by the primary winding 7 a, the snubber capacitor 10 and the diode 18, and charges are accumulated in the snubber capacitor 10. At this time, the voltage at both ends of the snubber capacitor 10 becomes a value obtained by dividing the electric charge by the capacity, but the sum of the value and the voltage of the DC power supply 5 becomes a voltage applied to the switch element 8, and thus exceeds the withstand voltage of the switch element 8. The capacity of the snubber capacitor 10 is selected so as not to occur.
[0003]
On the other hand, when the switch element 8 is turned on from the off state, the electric charge of the snubber capacitor 10 flows through a closed circuit formed by the snubber capacitor 10, the switch element 8, the diode 19, and the reactor 20. Resonance is generated by the snubber capacitor 10 and the reactor 20 while the switch element 8 is on, but the diode 19 ends in a half wave, so that the current rises from zero and ends at zero, and the snubber capacitor 10 has its resonance reversed in polarity. The same voltage as the previous voltage is charged. If the voltage of the snubber capacitor 10 at this time coincides with the voltage of the DC power source 5, the switch element 8 is turned off from the ON state, and the exciting energy of the transformer 7 becomes a current, so that the primary winding 7a and the snubber capacitor are turned on. When the current flows through a closed circuit formed by the diode 10 and the diode 18, the voltage of the switch element 8 rises from zero. If the voltage of the snubber capacitor 10 immediately before the switch element 8 is turned off is lower than the voltage of the DC power supply 5, the voltage rises from a voltage corresponding to the difference.
[0004]
[Problems to be solved by the invention]
The fact that the voltage rises from zero when the switch element 8 is turned off means that the current flowing through the switch element 8 decreases from the peak value to zero while the voltage across the switch element 8 is zero. The switching loss at turn-off can theoretically be reduced to zero. Further, while the current of the primary winding 7a falls from the peak value to zero, the current flows through a closed circuit formed by the primary winding 7a, the snubber capacitor 10 and the diode 18, so that the rate of change of current during turn-off becomes loose. Noise generation is suppressed.
[0005]
However, when the voltage of the snubber capacitor 10 immediately before the switch element 8 is turned on reaches the same value as the voltage of the DC power supply 5, the voltage applied to the switch element 8 during the OFF period of the switch element 8 is the voltage of the DC power supply 5. This means that the voltage is twice as high as that of the DC power source 5 because the switching element 8 has a withstand voltage. On the other hand, the higher the withstand voltage, the higher the cost of the switch element 8. Therefore, the capacity of the snubber capacitor 10 is selected so that the voltage of the snubber capacitor 10 is also lower than the voltage of the DC power supply 5. If the voltage of the snubber capacitor 10 immediately before the switch element 8 is turned on does not reach the voltage of the DC power supply 5, the switch element 8 is turned on and the inverted voltage does not reach the voltage of the DC power supply 5. Never stand up from scratch.
[0006]
Accordingly, an object of the present invention is to provide a circuit that always rises from zero volts when the switch element is turned off by appropriately combining a snubber capacitor, a reactor, and a diode. Another object of the present invention is to provide a circuit that always rises from zero volts when the switch element is turned off, even with respect to the voltage of the AC power supply that changes with time.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, a first aspect of the present invention is directed to a DC power source, a smoothing capacitor, a series circuit composed of a primary winding of a transformer and a switch element, and a control electrode of the switch element. And a snubber capacitor connected in parallel to the switch element, the first diode on the terminal side connected to the connection point between the smoothing capacitor of the snubber capacitor and the switch element. And a series circuit composed of a reactor and a second diode are inserted in series on the terminal side connected to the connection point of the smoothing capacitor and the switch element of the DC power source, and a series composed of the first diode and the reactor. Connect a third diode between the connection point of the circuit and the snubber capacitor and the connection point of the DC power supply and the second diode. .
[0008]
The invention according to claim 2 is connected to an AC power source, a full-wave rectifier, a smoothing capacitor, a series circuit composed of a primary winding of a transformer and a switch element, and a control electrode of the switch element. In a switching power supply device comprising a controlled oscillation circuit and a snubber capacitor connected in parallel to a switch element, a first diode and a reactor are connected to a terminal connected to a connection point between the smoothing capacitor of the snubber capacitor and the switch element. A series circuit comprising: a second diode connected between the connection point of the series circuit comprising the first diode and the reactor and the snubber capacitor, and one terminal of the AC power supply; A third diode was connected between the terminals.
[0009]
In the first aspect of the present invention, when the switch element is turned off from the ON state, the excitation energy of the transformer 7 flows through a closed circuit formed by the primary winding, the snubber capacitor, the third diode, and the DC power source, and charges the snubber capacitor. accumulate. Since this closed circuit is a series resonant circuit in which the current is one-way, the current starts from the current flowing through the primary winding immediately before the switch element is turned off, and ends at zero. Since the voltage across the snubber capacitor when the current becomes zero is higher than the voltage of the smoothing capacitor, the charge of the snubber capacitor is smoothed by the series circuit consisting of the first diode and the reactor, the snubber capacitor, the primary winding, and so on. It discharges through the closed circuit created by the capacitor. This closed circuit also rises from zero because the current is a one-way series resonant circuit and because the previous resonant current ends at zero. The period in which the current flows through the closed circuit continues until it becomes zero if the switch element is not turned on. However, when the switch element is turned on, the current path is changed from the middle to the first diode, the reactor, the snubber capacitor, and the switch element. Changes to a closed circuit.
[0010]
If the charge of the snubber capacitor continues to discharge and reaches zero while the switch element is on, the energy of the snubber capacitor will be zero, and instead, the reactor whose excitation energy has peaked will continue to flow current. However, the current flows through a closed circuit formed by a series circuit including a first diode and a reactor, a third diode, a DC power source, and a smoothing capacitor. The second diode secures a closed circuit at this time. The voltage across the snubber capacitor remains zero.
[0011]
When the switch element is turned off from the on state, the voltage across the snubber capacitor is zero, so the voltage applied to the switch element rises from zero. That is, soft switching is performed at the turn-off.
[0012]
According to the second aspect of the present invention, when the switch element is turned off from the ON state, the excitation energy of the primary winding is the primary winding, the snubber capacitor, any one of the second diode or the third diode, and the AC power source. It flows through the closed circuit created by the full-wave rectifier and accumulates electric charge in the snubber capacitor. The difference from the above description regarding the invention of claim 1 is that an AC power supply is used instead of a DC power supply, so that if the polarity of the AC voltage changes, the second diode enters the closed circuit or the third diode It is only a difference in entering, and the above explanation regarding the invention of claim 1 can be applied.
[0013]
Since the AC power supply is in the path through which the excitation energy flows, the problem that the conduction angle becomes narrow and the power factor decreases in the capacitor input type rectifier circuit can be improved.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the invention described in claim 1 will be described with reference to FIG. In FIG. 1, the voltage of the smoothing capacitor 6 is intermittently applied to the primary winding 7 a of the transformer 7 by the on / off operation of the switch element 8. A change in magnetic flux generated in the core of the transformer 7 due to the intermittent voltage is taken out as a voltage where the secondary winding 7b is intermittent, and is rectified and smoothed by the diode 11, the diode 12, the reactor 13, and the capacitor 14 to obtain a DC voltage. To supply. This embodiment is a wiring form called a forward converter.
[0015]
In FIG. 1, the excitation energy accumulated in the transformer 7 during the ON period of the switch element 8 flows via the snubber capacitor 10, the third diode 4, and the DC power supply 5 when the switch element 8 is turned off. Accumulate. The voltage across the snubber capacitor 10 is such that the potential at the point A in the figure is higher than the potential at the point B, the potential difference rises and exceeds the voltage of the DC power supply 5, and further reaches a peak, the charge of the snubber capacitor 10 becomes It flows down the series circuit which consists of the primary winding 7a, the smoothing capacitor 6, and the 1st diode 1 and the reactor 2, and it falls to the voltage of the DC power supply 5 eventually, and is stabilized.
[0016]
The snubber capacitor 10 remains in the snubber capacitor 10 even if the switch element 8 is turned on, whether the voltage of the snubber capacitor 10 is rising, falling, or lowered to the voltage of the DC power supply 5 and is stable. The electric charge flows through a closed circuit formed by a series circuit composed of the switch element 8 and the first diode 1 and the reactor 2 to be discharged.
[0017]
The discharge after the switch element 8 is turned on is initially a resonance current, but when the voltage across the snubber capacitor 10 becomes zero, that is, when the potential at the point B in the figure becomes zero, the excitation energy of the reactor 2 is reduced. The energy reaches a peak, and this energy flows through the third diode 4, the DC power supply 5, the smoothing capacitor 6, and the first diode 1, and increases the electric charge of the smoothing capacitor 6. Since the snubber capacitor 10 maintains zero volts until the switch element 8 is turned off, the snubber capacitor 10 is charged from zero when the switch element 8 is turned off, and the voltage of the switch element 8 rises from zero.
[0018]
FIG. 2 shows another embodiment of the present invention. Although the vertical positional relationship between the primary winding 7a of the transformer 7 and the switch element 8 is opposite to that of FIG. 1, the operation principle is the same as that of FIG.
[0019]
FIG. 3 shows an embodiment of the second aspect of the present invention. The embodiment of the invention according to claim 1 shown in FIG. 1 uses a DC power supply, whereas in FIG. 3 uses an AC power supply, the diode corresponding to the third diode 4 in FIG. In FIG. 3, they are the second diode 3 and the third diode 4. Further, the diode corresponding to the second diode 3 in FIG. 1 also serves as the bridge rectifier 17 in FIG.
[0020]
【The invention's effect】
By adding few components to the conventional switching power supply device, soft switching is achieved, and power loss and noise are improved, so the application range is wide and the economic effect is great.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a switching power supply device according to an embodiment of the present invention;
FIG. 2 is a circuit diagram showing a switching power supply device according to another embodiment of the invention as set forth in claim 1;
FIG. 3 is a circuit diagram showing a switching power supply device according to an embodiment of the invention as set forth in claim 2;
FIG. 4 is a circuit diagram showing an example of a conventional method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 1st diode 2 Reactor 3 2nd diode 4 3rd diode 5 DC power supply 6 Smoothing capacitor 7 Transformer 8 Switch element 9 Oscillation control circuit 10 Snubber capacitor 11, 12 Diode 13 Reactor 14 Capacitor 15 Load 17 Bridge rectifier 18, 19 Diode 20 Reactor 7a Primary winding 7b Secondary winding

Claims (2)

A DC power source, a smoothing capacitor, a series circuit composed of a primary winding of a transformer and a switch element, which forms a closed circuit with the smoothing capacitor, an oscillation control circuit connected to a control electrode of the switch element, and the switch element In a switching power supply device including a snubber capacitor connected in parallel, a second terminal is connected between a connection point of the smoothing capacitor and the switch element of the snubber capacitor and a connection point of the smoothing capacitor and the switch element. A series circuit composed of a diode and a reactor is inserted in series, and a terminal connected to a connection point between the smoothing capacitor and the switch element of the DC power supply is connected between a connection point between the smoothing capacitor and the switch element. 2 diodes are inserted in series, and the series circuit comprising the first diode and the reactor is inserted. And a snubber capacitor connection point and a third diode connected between the DC power supply and the second diode connection point, thereby switching the switching operation of the switch element to a soft switch. Power supply. An AC power source, a full-wave rectifier, a smoothing capacitor, a series circuit composed of a primary winding of a transformer and a switch element that forms a closed circuit with the smoothing capacitor, and an oscillation control circuit connected to a control electrode of the switch element; In the switching power supply device comprising a snubber capacitor connected in parallel to the switch element, a connection between the smoothing capacitor of the snubber capacitor and a connection point of the switch element, a connection between the snubber capacitor and the smoothing capacitor A series circuit composed of a first diode and a reactor is inserted in series between the points, and between the connection point of the series circuit composed of the first diode and the reactor, the snubber capacitor, and one terminal of the AC power supply. Connecting a second diode, and a series circuit comprising the first diode and the reactor; A third diode is connected between the connection point of the snubber capacitor and another terminal of the AC power supply, thereby making the switching operation of the switch element a soft switch and widening the conduction angle of the AC input current. A switching power supply characterized by improved power factor.

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