JP4644950B2 - Switching power supply - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a switching power supply device, and more specifically to a technique for reducing a ripple component included in an input current and an output current.
[0002]
[Prior art]
Conventionally, methods such as a half bridge and a full bridge have been used as means for reducing the ripple component of the input current and output current of the switching power supply.
[0003]
FIG. 5 shows the principle diagram of the half bridge, but the two switch elements 13a and 13b are alternately turned on and off alternately, and the two are not turned on at the same time. When the switch element 13a is on, the current supplied from the DC power source 21 passes through the primary winding 12a of the first transformer 12 and the capacitor 20b. At this time, current flows from the upper side to the lower side of the primary winding. When the switch element 13b is on, the current flows through the primary winding 12a and the capacitor 20a, but flows through the primary winding from the bottom to the top.
[0004]
Although the ON period of the switch elements 13a and 13b does not exceed 50% of the period, the current of the DC power supply can widen the conduction angle to nearly 100% as shown in FIG. As a result, the ripple component included in the current of the DC power supply 21 is reduced. The ripple component of the current flowing from the secondary windings 12b and 12d of the transformer to the second smoothing capacitor 16 is also reduced.
[0005]
By reducing the ripple component, there is an advantage that the power loss caused by the DC resistance component of the DC power supply 21 is reduced. When the DC power supply has a filter circuit composed of a capacitor and an inductor, the ripple current flowing through the capacitor is also reduced, so that the power loss due to the equivalent series resistance of the capacitor is also reduced. The same applies to the output current on the secondary side.
[0006]
[Problems to be solved by the invention]
However, the conventional method has a disadvantage that a circuit for driving the switch elements 13a and 13b becomes complicated.
[0007]
Therefore, the present invention provides a circuit that reduces the ripple component of the input current with a simpler circuit.
[0008]
[Means for Solving the Problems]
In the present invention, as shown in FIG. 1, a second flyback converter in which the first smoothing capacitor 11 of the first flyback converter and the second smoothing capacitor 16 on the secondary side are respectively shared is connected in parallel. And the second switch element 2 of the second flyback converter is appropriately connected based on the AC signal generated in the tertiary winding 12c of the first transformer 12 of the first flyback converter. It is turned on and off by a pulse generated by a circuit composed of a capacitor 5 and a resistor 6 having a long time constant and the third switch element 4.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The ON period of the first switch element 13 that is the switch element of the first flyback converter and the second switch element 2 that is the switch element of the second flyback converter are alternately shown in FIG. The polarity of the tertiary winding 12c is selected so that the ON period of the second switch element 2 does not overlap with the ON period of the first switch element 13. 6 is selected.
[0010]
The voltage of the capacitor 5 changes exponentially with respect to the voltage generated in the tertiary winding 12c as shown in FIG. The ON period of the second switch element 2 is given by t2 in the figure. That is, when the voltage of the capacitor 5 reaches the threshold value of the control electrode of the third switch element 4, the third switch element 4 is turned on and the second switch element 2 is turned off. By appropriately selecting the voltage of the number of turns 12c and the values of the capacitor 5 and the resistor 6, the second switch element 2 can be turned off before the first switch element 13 is turned on.
[0011]
【Example】
FIG. 1 is a circuit showing an embodiment of the first aspect of the present invention.
[0012]
In FIG. 1, the first switch element 13 is repeatedly turned on and off by pulses output from the oscillation control circuit 14, and supplies a constant DC voltage to the load 17 through the first transformer 12.
[0013]
The second switch element 2 is repeatedly turned on / off by a pulse generated in the tertiary winding 12c wound around the first transformer 12, but the phase is reversed from the on / off state of the first switch element 13. The ON period of the second switch element 2 is limited by the third switch element 4, the capacitor 5 and the resistor 6, and is turned off before the first switch element 2 is turned on.
[0014]
The currents flowing through the first switch element 13 and the second switch element 2 are out of phase and do not overlap each other, so that the conduction angle of the input current is widened and the ripple component is reduced. Also, on the secondary side, current flows alternately through the first diode 15 and the second diode 7, so that the conduction angle is widened and the ripple component is reduced.
[0015]
In FIG. 1, the impedance element 3 may be a resistor, but may be a circuit in which a capacitor and an inductor are combined in addition to the resistor.
[0016]
In FIG. 1, MOSFETs are selected for the first switch element 13 and the second switch element 2, and bipolar transistors are selected for the third switch element 4. However, these may be replaced with different types of switch elements. Is possible.
[0017]
In FIG. 1, the oscillation control circuit 14 may be fixed in frequency or may be self-excited oscillation.
[0018]
FIG. 2 is a circuit diagram showing an embodiment of the second aspect of the present invention.
[0019]
In FIG. 2, a circuit composed of the second transformer 1 and the second switch element 2 is connected to an AC power source 8 via a center tap diode 9. This improves the power factor because current flows over an angle of 360 ° of the alternating current phase.
[0020]
【The invention's effect】
Conventionally, the power range in which the flyback converter can be applied has been considered to be 200 W due to cost limitations. However, since the ripple component included in the input current is greatly reduced by the present invention, both the primary side and the secondary side are included. The load on the electrolytic capacitor is reduced, and it can be applied to a power supply of 200 W or more at the same cost as a half bridge or a full bridge. In addition, when the secondary voltage exceeds 24V, the flyback method may be preferred rather than the limitation of the withstand voltage of the secondary diode. It can be expected as an alternative method.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an embodiment of the invention as set forth in claim 1;
FIG. 2 is a circuit diagram showing an embodiment of the invention as set forth in claim 2;
FIG. 3 is a waveform diagram of FIG. 1;
4 is a waveform diagram of FIG. 1. FIG.
FIG. 5 is a circuit diagram showing an example of a conventional method.
6 is a waveform diagram of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 2nd transformer 1a Primary winding 1b Secondary winding 2 2nd switch element 3 Impedance element 4 3rd switch element 5 Capacitor 6 Resistance 7 2nd diode 8 AC power supply 9 Center tap diode 10 Full wave rectifier 11 First smoothing capacitor 12 First transformer 12a Primary winding 12b Secondary winding 12c Tertiary winding 12d Secondary winding 13 First switch element 13a Switch element 13b Switch element 14 Oscillation control circuit 15 First Diode 16 second smoothing capacitor 17 load 18 reactor 19 diode 20a capacitor 20b capacitor 21 DC power supply

Claims (2)

An alternating current power supply, a full wave rectifier that converts an alternating current supplied from the alternating current power supply into a direct current, a first smoothing capacitor that accumulates the direct current converted by the full wave rectifier and converts it into a direct current voltage; A first circuit of the first transformer connected in parallel to the first smoothing capacitor and a series circuit composed of a first switch element and electromagnetically coupled to the primary winding of the first transformer. The wound secondary winding , the first diode connected in series to the secondary winding of the first transformer, and the first AC voltage generated in the secondary winding of the first transformer A second smoothing capacitor that charges a component that passes through the diode, a load that supplies the voltage of the second smoothing capacitor, and a voltage of the first smoothing capacitor to keep the voltage of the second smoothing capacitor constant. Oscillation control to control oscillation In a flyback converter having a path, a second transformer having a primary winding and a secondary winding is connected with one end of the primary winding connected to one terminal of the first smoothing capacitor and the other end. Each terminal is connected to the other terminal of the first smoothing capacitor via a second switch element, and one end of the secondary winding is connected to one terminal of the second smoothing capacitor via a second diode. In addition, another end is connected to the other terminal of the second smoothing capacitor, a tertiary winding electromagnetically coupled to the primary winding of the first transformer is wound, and the impedance element is connected to the one end. The other end of the second switch element is connected to the source of the second switch element, a transistor is connected between the gate and the source of the second switch element, and the base of the transistor And Jitter and a capacitor is connected between said third winding of the switching power supply device, wherein a resistor is connected between the base of the terminal and the transistor impedance elements are connected. The switching power supply device according to claim 1, wherein one end of the primary winding of the second transformer is connected to each terminal of the AC power supply via a center tap diode.

Images