JP2004304970A - Switching power supply unit and control method for voltage conversion - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching power supply unit wherein stable direct-current output voltage free from ripple voltage or the like is obtained, the circuitry is simplified, and the cost can be reduced. <P>SOLUTION: The switching power supply unit is so constituted that the following operation is performed: Input voltage is charged into a smoothing capacitor through a reactor; the charging voltage is alternately chopped by a transformer and two switching elements at a predetermined frequency; and alternating voltage of a predetermined frequency is produced on the output side of the transformer, and is rectified and outputted. More specifically, a current is passed through the reactor via one in the on state of the two switching elements. When the state of the switching element in the on state changes to the off state, the energy stored in the reactor is applied in a superposing manner to the capacitor to boost the charging voltage. The boosted charging voltage is input to the input side of the transformer through the other switching element whose state changes from the off state to the on state. Thus, alternating voltage of the predetermined frequency is produced on the output side of the transformer. The alternating voltage is rectified and outputted. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a switching power supply device that chops a DC input voltage at a predetermined frequency by a switching element, rectifies the DC input voltage with an output-side rectifier circuit, and outputs a predetermined DC output voltage, and a voltage conversion control method therefor.
[0002]
[Prior art]
Conventionally, as this kind of switching power supply device, there is a switching power supply device disclosed in the following Patent Document 1, and as shown in FIG. 6, a boost converter (or a pre-converter) is provided in a stage preceding a smoothing capacitor. These are all configured to improve the power factor.
[0003]
[Patent Document 1]
Japanese Patent No. 3082873 [0004]
The conventional circuit shown in FIG. 6 performs full-wave rectification on an AC power supply voltage by a rectifier circuit RC1 including diodes D1 to D4, and supplies the DC output voltage to a smoothing capacitor C1 through a series circuit of a reactor L1 and a diode D5. A transistor TR0, which is configured to charge the smoothing capacitor C1 and has a conduction path (collector / emitter) connected to a connection point between the reactor L1 and the diode D5, is controlled by a control signal of a predetermined frequency sufficiently higher than the AC power supply frequency. When the switching is performed, when the transistor TR0 changes from ON to OFF, the energy generated from the reactor L1 is superimposed on the smoothing capacitor C1 through the diode D5 and charged, and the charging voltage of the smoothing capacitor C1 is boosted from the output voltage of the rectifier circuit. The boosted voltage is applied to the primary winding N1, 2 and chopped by transistors TR1 and TR2, and connected to secondary windings N3 and N4 of transformer T1 from diodes D6 and D7, reactor L2, smoothing capacitor C2, and rectifier circuit RC2 composed of resistor R1. It is configured to output a predetermined DC output voltage.
[0005]
The transistor TR0 is switched at a frequency sufficiently higher than the AC power supply frequency by the control signal output from the first control circuit CONT1. FIGS. 7 (a) to show the waveform of the collector voltage _{V TR0} transistor TR0, shows the waveform of the current _{I TR0} flowing between the emitter and the collector in Fig. 7 (b).
The control circuit CONT1 monitors the charging voltage of the smoothing capacitor C1, and controls the ON time of the transistor TR1 so that the charging voltage becomes a predetermined voltage.
On the other hand, one end of the first winding N1 and the second winding N2 on the primary side of the transformer T1 are connected to each other, and the other end of the first winding N1 is connected to the collector of the transistor TR1. The other end of the second winding N2 of the transformer T1 is connected to the collector of the transistor TR2.
[0006]
The control circuit CONT2 switches the transistors TR1 and TR2 so that the output voltage of the rectifier circuit REC2 on the output side is maintained at a predetermined voltage by a control signal having a frequency slightly different from that of the control circuit CONT1, and the primary side of the transformer T1 is switched. A current obtained by chopping the output voltage of the smoothing capacitor C2 at a predetermined frequency is alternately supplied to the first winding N1 and the second winding N2. Figure 7 (c) to show the waveform of the collector voltage _{V TR2} transistors TR2, shows the waveform of the current _{I TR2} flowing between the emitter and the collector in Fig. 7 (d). The collector voltage and the collector current of the transistor TR2 are out of phase with the transistor TR2, and are omitted in FIG.
Further, since the boost converter and the push-pull type converter operate by independent control circuits, they operate at their own oscillation frequencies. The operation in FIG. 7 is illustrated with the phases adjusted for convenience.
[0007]
[Problems to be solved by the invention]
However, in the conventional device of FIG. 6, a boost converter composed of a transistor TR0 and a control circuit CONT1 provided in the preceding stage of the smoothing capacitor C1 and a push-pull converter using the transistors TR3, TR4 and the transformer T1 in the subsequent stage are used. Since they are operated at different switching frequencies, if the two switching frequencies are close to each other, slight oscillation of one of the switching frequencies causes beat oscillation, and a ripple voltage appears at the output of the rectifier circuit RC1 on the output side. This causes a problem that an external device connected to the output may malfunction.
Further, since two control circuits are provided, there is a problem that the circuit configuration becomes large and the cost increases.
[0008]
The present invention has been made in order to solve such a problem, and an object of the present invention is to obtain a stable DC output voltage that does not generate a ripple voltage and the like, and to further simplify a circuit configuration and reduce costs. And a voltage conversion control method therefor.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a reactor having one end connected to an input terminal of a DC input voltage, and one end connected to a first winding and a second winding on a primary side having one end connected to each other. Transformer having a secondary third winding and a fourth winding, and an output rectifier circuit connected to the other end of the secondary third winding and the other end of the fourth winding. A first diode having an anode connected to the other end of the reactor, a cathode connected to the other end of a first winding on the primary side of the transformer, and an anode connected to the other end of the reactor; A second diode connected to a connection point between the first and second windings on the primary side of the transformer, an anode connected to the other end of the reactor, and a cathode connected to the second side on the primary side of the transformer. A third diode connected to the other end of the winding, the second die A capacitor connected to the cathode of the first diode, a first switching element having a conductive path connected between the cathode of the first diode and the ground potential, and a capacitor connected to the cathode of the third diode and the ground potential. A second switching element having a conductive path connected therebetween; and a control circuit for driving the first and second switching elements with a control signal of a predetermined frequency provided with a period in which the first and second switching elements are turned on alternately. And
A fourth diode having an anode on the second diode side is connected between a cathode of the second diode and a connection point between the first winding and the second winding on the primary side of the transformer. It is characterized by having.
[0010]
In the voltage conversion control method according to the present invention, an input voltage is charged to a smoothing capacitor via a reactor, and the charged voltage is alternately chopped at a predetermined frequency by a transformer and two switching elements. In a switching power supply that generates an alternating voltage, rectifies the alternating voltage, and outputs the rectified voltage, a current flows through the reactor through a switching element that is on between the two switching elements, and the reactor is turned on. When the switching element changes to the off state, the energy stored in the reactor is superimposed and applied to the smoothing capacitor to boost the charging voltage of the smoothing capacitor, and the boosted charging voltage is changed from the off state to the on state. Input to the input side of the transformer via the other switching element Wherein the transformer output side generates an alternating voltage of a predetermined frequency, and outputs rectifies the alternating voltage.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be specifically described with reference to the drawings.
FIG. 1 is a circuit diagram showing an embodiment of a power supply device according to the present invention. In FIG. 1, the same parts as those of the conventional circuit of FIG. 1 are denoted by the same reference numerals.
The switching power supply device of the present embodiment shown in FIG. 1 includes a reactor L1 connected to an output terminal (input terminal of a DC input voltage) of a rectifier circuit RC1, a primary-side first winding N1 connected to one end and a first winding N1. It has a second winding N2 and a third winding N3 and a fourth winding N4 on the secondary side, one end of which is connected to each other. The other end of the third winding N3 on the secondary side and the fourth winding N4 A transformer T1 having the other end connected to the rectifier circuit RC2 on the output side, an anode connected to the other end of the reactor L1, and a cathode connected to the other end of the first winding N1 on the primary side of the transformer T1. A first diode D8, an anode connected to the other end of the reactor L1, and a cathode connected to a connection point between the first winding N1 and the second winding N2 on the primary side of the transformer T1. A diode D5 and the anode are the reactor L A third diode D9 having a cathode connected to the other end of the second winding N2 on the primary side of the transformer T1, and a smoothing capacitor C1 connected to the cathode of the second diode D5. And a first transistor TR1 having a conductive path (emitter-collector) connected between the cathode of the first diode D8 and the ground potential, and between the cathode of the third diode D9 and the ground potential. A second transistor TR2 to which a conductive path is connected, and a control circuit CONT for driving the first and second transistors TR1 and TR2 with a control signal of a predetermined frequency provided with a period in which the transistors TR1 and TR2 are alternately turned on. I have.
[0012]
The difference from the conventional circuit of FIG. 6 is that the transistors TR0 and the control circuit CONT1 are deleted, while diodes D8 and D9 are added.
By connecting the diodes D8 and D9 to the collectors of the transistors TR1 and TR2, when the transistors TR1 and TR2 are ON, the transistors TR1 and TR2 play the role of the conventional booth and the transistor TR0 of the converter, and transfer energy to the reactor L1. Responsible for storing. It has a circuit configuration in which a conventional boost converter and a push-pull converter are combined.
The diode D5 prevents the charging voltage of the smoothing capacitor C1 from flowing backward. The diodes D8 and D9 prevent the current flowing through the first winding N1 and the second winding N2 on the primary side of the transformer T1 from flowing back into the smoothing capacitor C1.
[0013]
The transistors TR1 and TR2 are switched by control signals CS1 and CS2 of the control circuit CONT. The control circuit CONT monitors the output voltage of the rectifier circuit RC2 on the output side, and controls the ON time of the transistors TR1 and TR2 so that the output voltage is kept constant. That is, when the output voltage of the rectifier circuit RC2 drops below a predetermined voltage, control is performed so as to increase the ON time, and when the output voltage exceeds the predetermined voltage, control is performed so as to shorten the ON time. Note that one cycle of switching is constant.
[0014]
Figure 2 is a diagram showing a waveform of a control circuit control signal CS2, CS1 that CONT is output, the collector voltage _V TR2 of the transistor TR2, _{TR1, V TR1,} collector current _{I TR2, I TR1.}
[0015]
Hereinafter, the operation of the embodiment of FIG. 1 will be described with reference to this waveform diagram.
First, as shown in FIGS. 2A and 2B, the control circuit CONT outputs a control signal for turning on the transistors TR1 and TR2 at a predetermined cycle (for example, 20 μs). Thus, the transistors TR1 and TR2 are switched at a frequency sufficiently higher than the frequency of the AC input voltage.
On the other hand, the smoothing capacitor C1 is charged via the diode D5 while the rectified output voltage of the rectifier circuit RC1 on the input side is applied to one end of the reactor L1.
[0016]
As shown in FIG. 2C, when a control signal CS2 for turning on the transistor TR2 at time t1 is input from the control circuit CONT to the base of the transistor TR2, the transistor TR2 turns on, and the reactor passes through the transistor TR2 in the ON state. The current in the path of L1 → diode D9 → transistor TR2 → ground potential and the current in the path of smoothing capacitor C1 → second winding N2 of transformer T1 → transistor TR2 → ground potential flow. FIG. 2D shows the collector current ITR2 in this state. At this time t1, the transistor TR2 is in the ON state, so that the collector voltage VTR2 is at the ground potential as shown in FIG.
Further, a current flows through reactor L1 through the path of diode D9 → transistor TR2 → ground potential, and energy is stored.
[0017]
Is the time t2, when the transistor TR2 is turned OFF by the control signal CS2, the stops flowing in the path of the current, the collector voltage _{V TR2} of the transistor TR2 is increased to the charge voltage of the smoothing capacitor C1, as shown in FIG. 2 (c) I do.
When the transistor TR2 changes from ON to OFF, the energy stored in the reactor L1 is applied to the smoothing capacitor C1 through the diode D5. As a result, the energy accumulated in the reactor L1 is superimposed on the rectified output voltage of the rectifier circuit RC1 and added to the smoothing capacitor C1, and the charging voltage of the smoothing capacitor C1 is boosted to the step-up level L2. To rise. As a result, the collector voltage _{V TR2} of the transistor TR2 is turned OFF also increases until the step-up level L2 as shown in FIG. 2 (c).
[0018]
With the charging voltage of the smoothing capacitor C1 at the step-up level L2, the transistor TR1 is turned on by the control signal CS1 at time t3. Then, a current flows through the path of the output of the smoothing capacitor C1, the first winding N1 of the transformer T1, the transistor TR1, and the ground potential. That is, a current in the direction of arrow B flows through the first winding N1 of the transformer T1. FIG. _2F shows the collector current _ITR1 of the transistor T1 at this time, and FIG. _2E shows the collector voltage _VTR1 .
The current flowing through the first winding N1 of the transformer T1 in the direction of the arrow B is higher than the case where the current is charged only with the rectified output voltage of the rectifier circuit RC1 because the charging voltage of the smoothing capacitor C1 is boosted to the step-up level L2. , The current value is large.
As a result, the DC output voltage of the rectifier circuit RC2 on the secondary side of the transformer T1 becomes proportional to the current value flowing in the arrow B direction through the first winding N1 of the transformer T1.
Further, since the transistor TR1 is ON, a current flows through the reactor L1 through a path from the diode D8 to the transistor TR1 to the ground potential, and energy is stored.
[0019]
Next, at time t4, when the transistor TR1 changes from ON to OFF, the current energy stored in the reactor L1 is applied to the smoothing capacitor C1 through the diode D5. As a result, the current energy accumulated in the reactor L1 is superimposed on the rectified output voltage of the rectifier circuit RC1 and added to the smoothing capacitor C1, so that the charging voltage of the smoothing capacitor C1 is boosted and the step-up level L2 To rise. As a result, the collector voltage _{V TR2} of the transistor TR1 is turned OFF also increases until the step-up level L2 as shown in FIG. 2 (e).
[0020]
While the charging voltage of the smoothing capacitor C1 is at the step-up level L2, the transistor TR1 is turned on by the control signal CS1 at time t5. Then, a current flows through the path of the output of the smoothing capacitor C1, the second winding N2 of the transformer T1, the transistor TR2, and the ground potential. That is, a current in the direction of arrow A flows through the second winding N1 of the transformer T1. The collector current _{I TR1} of the transistor TR1 at this time in FIG. 2 (d), shows the collector voltage _{V TR1} in Figure 2 (c).
The current flowing through the second winding N2 of the transformer T1 in the direction of arrow B is higher than the case where the current is charged only with the rectified output voltage of the rectifier circuit RC1 because the charging voltage of the smoothing capacitor C1 has been boosted to the step-up level L2. , The current value is large.
As a result, the DC output voltage of the rectifier circuit RC2 on the secondary side of the transformer T1 becomes proportional to the value of the current flowing through the second winding N2 of the transformer T1 in the direction of arrow A.
Thereafter, the above operation is similarly repeated.
[0021]
As can be seen from the above, in the present embodiment, the current is supplied to the reactor L1 via the diodes D8 and D9 by utilizing the period in which the transistors TR1 and TR2 are ON, and the current energy for boosting is stored. The stored current energy is superimposed on the smoothing capacitor C1 and added to the smoothing capacitor C1 at the next time when the transistor that has been in the ON state changes to the OFF state, and the charging voltage of the smoothing capacitor C1 is boosted. The voltage is caused to flow through the primary winding (N1 or N2) of the transformer T1 through the transistor that has changed from the OFF state to the ON state, and a predetermined DC voltage is output from the rectifier circuit RC2 on the secondary side of the transformer T1. Things.
[0022]
As described above, only by adding the diodes D8 and D9, the number of control circuits is reduced to one, and the cost can be reduced. In addition, since one control circuit is provided, malfunction such as beat oscillation does not occur, and a stable output voltage can be output from the output.
[0023]
Here, if the time of the current flowing through the reactor L1 becomes long, the reactor L1 may be magnetically saturated, and may not function as the reactor L1. In implementation, it is desirable to select the inductance value of reactor L1 and the switching frequency of transistors TR1 and TR2 so that magnetic saturation of reactor L1 does not occur.
That is, as shown in FIGS. 3E and 3F, if the input voltage of the next cycle is input to reactor L1 before the energy stored in reactor L1 is released (reset), the current of reactor L1 does not become zero. , A phenomenon of continuous flow occurs. This is called a continuous current mode. Further, as shown in FIGS. 3C and 3D, when an input voltage of the next cycle is input immediately after the current of the reactor L1 becomes zero or immediately before it becomes zero, the critical point of the current continuous mode is reached. An operating phenomenon occurs. These phenomena cause magnetic saturation of the reactor L1, and the reactor does not normally function properly.
Therefore, as shown in FIGS. 3A and 3B, the energy stored in the reactor L1 is sufficiently released, and the reactor L1 is operated in the current discontinuous mode in which a current discontinuous period in which a zero current value continues for a certain period can be secured. It is desirable to select the inductance value of the reactor L1 and the switching frequency of the transistors TR1 and TR2 so as to drive. By driving the reactor L1 in the discontinuous current mode, magnetic saturation of the reactor can be reliably prevented, so that the power factor on the input side can be improved.
FIG. 2 (g) shows a current waveform of the reactor L1.
[0024]
In the configuration of FIG. 1, the DC output voltage of the rectifier circuit RC1 for rectifying the AC power supply voltage is input to the reactor L1, but as shown in the second embodiment of FIG. It can also be configured to input. With such a configuration, it can be used as a DC / DC converter.
[0025]
Further, when both the transistors TR1 and TR2 are OFF, a current flowing backward from the primary winding of the transformer T1 to the smoothing capacitor C1 may flow for some reason. However, as shown in the third embodiment in FIG. As described above, the diode D10 is connected between the connection point between the first winding N1 and the second winding N2 of the transformer T1 and the cathode of the diode D5, and the current flowing back to the smoothing capacitor C1 is cut off to thereby provide a transistor. By stabilizing the charging voltage of the smoothing capacitor C1 when both TR1 and TR2 are OFF, the output voltage of the rectifier circuit RC2 on the secondary side can be stabilized.
[0026]
In principle, the switching power supply device of the embodiment described above can be restated as the following voltage conversion control method.
That is, an input voltage is charged to a smoothing capacitor via a reactor, and the charged voltage is alternately chopped at a predetermined frequency by a transformer and two switching elements to generate an alternating voltage of a predetermined frequency at an output side of the transformer. In a voltage converter that rectifies and outputs a voltage, a current flows through the reactor through a switching element that is in an on state of the two switching elements, and a switching element that has been in an on state changes to an off state. The other switching element that superimposes and applies the current energy stored in the reactor to the smoothing capacitor to boost the charging voltage of the smoothing capacitor, and changes the boosted charging voltage from an off state to an on state. Input to the input side of the transformer via the To generate a number of alternating voltage, and outputs the rectified its alternating voltage.
[0027]
【The invention's effect】
As described above, according to the present invention, it is possible to obtain a stable DC output voltage that does not generate a ripple voltage or the like, and further, reduces the number of control circuits from two to one, simplifies the circuit configuration, and reduces cost. Can be done.
[Brief description of the drawings]
FIG. 1 is a circuit configuration diagram showing a first embodiment of a switching power supply device to which the present invention is applied.
FIG. 2 is a waveform chart of each part showing an operation in a normal state in the configuration of FIG. 1;
FIG. 3 is a waveform diagram illustrating a continuous current mode and a discontinuous mode of the reactor in the configuration of FIG. 1;
FIG. 4 is a circuit configuration diagram showing a second embodiment of the present invention.
FIG. 5 is a circuit configuration diagram showing a third embodiment of the present invention.
FIG. 6 is a circuit configuration diagram of a conventional switching power supply device.
FIG. 7 is a waveform diagram illustrating the operation of a conventional switching power supply device.
[Explanation of symbols]
RC1 ... rectifier circuit on the input side, RC2 ... rectifier circuit on the output side, D1 to D4 ... diodes on the input side rectifier circuit, L1 ... reactor, D6 to D7 ... diodes on the output side rectifier circuit, D5, D8, D9 ... diodes. C1: smoothing capacitor, TR1, TR2: transistor, T1: transformer, CONT: control circuit, E: battery, D10: diode.

Claims (3)

In a switching power supply device, a DC input voltage is chopped at a predetermined frequency by a switching element, rectified by an output rectifier circuit, and outputs a predetermined DC output voltage.
A reactor having one end connected to the input end of the DC input voltage,
A primary-side first winding and a second winding having one ends connected to each other, and a secondary-side third winding and a fourth winding having one ends connected to each other, and a secondary-side third winding A transformer having a rectifier circuit on the output side connected to the other end of the fourth winding and the other end of the fourth winding;
A first diode having an anode connected to the other end of the reactor and a cathode connected to the other end of the first winding on the primary side of the transformer;
A second diode having an anode connected to the other end of the reactor, and a cathode connected to a connection point between a first winding and a second winding on the primary side of the transformer;
A third diode having an anode connected to the other end of the reactor and a cathode connected to the other end of the second winding on the primary side of the transformer;
A capacitor connected to the cathode of the second diode;
A first switching element having a conductive path connected between a cathode of the first diode and a ground potential;
A second switching element having a conductive path connected between the cathode of the third diode and ground potential;
And a control circuit for driving the first and second switching elements with a control signal of a predetermined frequency provided with a period in which the first and second switching elements are turned on alternately. A fourth diode having a second diode as an anode is connected between a cathode of the second diode and a connection point between a first winding and a second winding on a primary side of the transformer. The switching power supply device according to claim 1, wherein: An input voltage is charged to a smoothing capacitor via a reactor, and the charged voltage is alternately chopped at a predetermined frequency by a transformer and two switching elements to generate an alternating voltage of a predetermined frequency at an output side of the transformer, and the alternating voltage is generated. In a switching power supply device that rectifies and outputs, when a current flows through the reactor via the on-state switching element of the two switching elements, the on-state switching element changes to the off state. The energy stored in the reactor is superimposed and applied to the smoothing capacitor to boost the charging voltage of the smoothing capacitor, and the boosted charging voltage is changed from the off state to the on state via the other switching element. Input to the input side of the transformer, and output a predetermined frequency to the output side of the transformer. An alternating voltage is generated in the voltage conversion control method and outputting rectifies the alternating voltage.

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