JP2984519B2 - Switching power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching type stabilized DC power supply having an AC input.

[0002]

2. Description of the Related Art FIG. 8 shows a first configuration of a conventional AC input switching power supply. A conventional AC input switching power supply comprises a commercial AC power supply 1, a full-wave rectifier 2, diodes 3, 4, 5, 6, a smoothing capacitor 7, a transformer 8, and its primary winding. 9, a secondary winding 10, a switch element 11, a rectifying and smoothing circuit 12, a load 13, and a control circuit 14. The operation of the first configuration of this conventional AC input switching power supply is as follows. The input of the commercial AC power supply 1 is rectified by a full-wave rectifier 2 and smoothed by a smoothing capacitor 7 to a DC having little ripple. By turning on and off at a frequency higher than the input commercial AC frequency, an AC voltage is applied to the primary winding 9 of the transformer 8 and its output is applied from the secondary winding 10 of the transformer 8 to the rectifying and smoothing circuit. Rectified and smoothed, and load 1 as a DC output voltage.
Give to 3. Here, the control circuit 14 detects the output voltage of the rectifying / smoothing circuit 12, and turns on and off the switch element 11 so that the output voltage becomes a predetermined voltage. As described above, this configuration has a function of replacing the input of the commercial AC power supply 1 with a stable DC voltage and outputting the DC voltage.

(3) FIG. 9 shows a second configuration of a conventional AC input switching power supply. 8, the same components as those of FIG. 8 are denoted by the same reference numerals, and the description thereof will be omitted. The difference from the configuration of FIG.
The boost chopper circuit 15 includes an inductor 16, a switch element 17, a diode 18, and a control circuit 19 for the boost chopper circuit 15. The control circuit 19 of the boost chopper circuit 15 is a control circuit that controls the output voltage of the boost chopper circuit 15, that is, the voltage of the smoothing capacitor 7 to a constant value. The operation of the second conventional configuration is such that the switching element 17 repeats the operation of turning on and off at a frequency higher than the input commercial AC frequency, storing the current in the inductor 16 at the time of on, and discharging the current at the time of off. The waveform of Iin (2) is approximated to a sine wave of a voltage waveform. Therefore, a power supply having a high power factor can be configured.

[0004]

However, the conventional two configurations have the following problems. FIG. 10 shows operation waveforms of the first configuration of the conventional AC input switching power supply.
In the figure, Vin (1) indicates the output voltage of the full-wave rectifier 2 with respect to the voltage of the commercial AC power supply 1, and Iin (1) indicates the waveform of the input current from the commercial AC power supply 1. As can be seen from the figure, the first configuration has a problem that the input current is surged and the power factor is extremely low. FIG. 11 shows operation waveforms of the second configuration of the conventional AC input switching power supply. In the figure, Vin (2) indicates the output voltage of the full-wave rectifier 2 with respect to the voltage of the commercial AC power supply 1, and Iin (2) indicates the waveform of the input current from the commercial AC power supply 1. As can be seen from the figure, in the second configuration, the line connecting the peak values of the input current approximates the sine wave of the input voltage, so that the line immediately before the full-wave rectifier 2
Immediately after that, if a low-pass filter for removing high-frequency ripple is used, the input current can be made approximately sinusoidal,
A power supply with a high power factor can be realized.

However, as shown in FIG. 9, a boost chopper circuit 15 is used to increase the power factor, and the inductor 16 and the diode (4) 18 are different from the conventional first configuration. , The switch element 17 and the control circuit 19 are required, and the control circuit is divided into two systems. Further, since the step-up chopper circuit 15 is used, the output voltage of the step-up chopper circuit 15, that is, the voltage of the smoothing capacitor 7 becomes higher than the commercial AC input voltage V. Since the switching element having a high withstand voltage must be used and has a large on-resistance, the voltage generated between the terminals of the switching element 11 when the switching element 11 is turned on increases, and the power consumed there increases to increase the switching power supply. However, there is a problem that the efficiency of the method is reduced.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has as its object to provide a high power factor, high efficiency AC input switching power supply having a simple structure comprising a set of switch elements and a control circuit. And

[0007]

According to the present invention, a smoothing capacitor is connected between output terminals of a full-wave rectifier connected to an AC power supply, and a primary winding of a transformer is connected between the terminals of the smoothing capacitor. The rectifying and smoothing circuit 35 is connected to the secondary winding 29 of the transformer 27, and power is supplied to a load 40 connected to the output terminal of the rectifying and smoothing circuit 35. In a switching power supply, an inductor 26 and a control winding 31 of the transformer are connected in series between the full-wave rectifier 21 and the smoothing capacitor 32.

[0008]

FIG. 1 shows an embodiment of the present invention. The configuration of the present embodiment comprises a commercial AC power supply 1, a full-wave rectifier 21, a first diode 22, a second diode 23, a third diode 24 constituting the full-wave rectifier 21, 4th Dio
(5) inductor 26, transformer 27 and its primary winding 28, secondary winding 29, tertiary winding 30, control winding 31, smoothing capacitor 3
2. Fifth diode 33, switch element 34, rectifying / smoothing circuit 35, and sixth diode 3 constituting the same.
6, a seventh diode 37, an inductor 38, a capacitor 39, a load 40, and a control circuit 41.

This operation is as follows. Transformer 27
The primary winding 28 has N1, the secondary winding 29 has N2, the tertiary winding 30 has N3, and the control winding 31 has N.
4, and the potentials at points a, b, and c in FIG. 1 are Va, Vb, and Vc, respectively. Here, if N1 = N4,
When the switch element 34 is on, the voltage of the smoothing capacitor 32, that is, Vb, is applied to the primary winding 28 of the transformer 27. At this time, V is applied to the fourth winding 31 of the transformer 27.
Although a voltage of b × N4 / N1 is generated, since N1 = N4, this is almost equal to Vb. So, a
The voltage Va at the point becomes zero volts when the voltage Vb generated in the control winding 31 of the transformer 27 is subtracted from the voltage Vb of the smoothing capacitor 32. That is, when the switch element 34 is on, a
The potential at the point is always zero volts. When the switch element 34 is turned on, the current flows in the circuit first from the smoothing capacitor 32 to the primary winding 28 of the transformer 27, to the secondary winding 29, and to the rectifying and smoothing circuit 35. Load 40
, And returns to the primary winding 28 of the transformer, flows through the switch element 34, and thereby transmits the energy of the smoothing capacitor 32 to the load 40. Further, when the switch element 34 is on, the voltage Va at the point a is always zero volt, so that the input voltage Vin (3) is applied to the inductor 26, the inductance of the inductor 26 is L26, and the current flowing through the inductor 26 is IL. (on), and the time after the switch element 34 is turned on is t.

(Equation 1) Flows through the inductor 26. This current first flows through the control winding 31 of the transformer (6) 27, and as a result, flows through the primary winding 28 of the transformer 27 and then through the switch element 34. With such a current flow, the commercial AC power supply 2
Zero energy is stored in inductor 26.

Next, when the switch element 34 is off, the tertiary winding 30 of the transformer 27 is used to reset the transformer.
And a current flows into the smoothing capacitor 32 via the diode 33. At this time, the voltage Vb of the smoothing capacitor 32 is applied between the terminals of the tertiary winding 30 of the transformer 27.
As a result, the voltage VN4 (off) generated in the control winding 31 of the transformer 27 becomes

(Equation 2) Becomes Therefore, the voltage Va (off) at point a is

(Equation 3) This result → the input voltage Vin is applied to the inductor 26.
The difference voltage from (3), that is,

(Equation 4) Is applied, and the current flowing through the inductor 26 decreases. When the switch element 34 is turned off, the current flows in the circuit. First, the current for resetting the transformer 27 is supplied from the tertiary winding 30 of the transformer 27 via the diode 33. The current of the inductor 26 flows into the smoothing capacitor 32 via the control winding 31 of the transformer 27 while the switch element 34 is off, and at the same time, the control winding of the transformer 27 is turned off. As a result of flowing through the line 31, a corresponding current flows from the tertiary winding 30 of the transformer 27 through the diode 33 into the smoothing capacitor 32. That is, with such a current flow, when the switch element 34 is in the OFF period, the excitation energy of the transformer 27 is sent to the smoothing capacitor 32 to reset the transformer 27, and at the same time,
The energy stored in the inductor 26 is sent to the smoothing capacitor 32. At the same time as the above operation, the control circuit 41 controls the switching element 34 by changing the ON and OFF periods so that the output voltage of the rectifying / smoothing circuit 35 becomes a predetermined voltage. (7)

FIG. 7 is an operation waveform diagram of each part of the embodiment of the present invention (FIG. 1). As described above, the input voltage Vin (3) is connected between the terminals of the inductor 26 while the switch element 34 is on. Is applied, and when the switch element 34 is off,

(Equation 5) Is applied, first, the current of the inductor 26 when the switch element 34 is on is as described above.

## EQU1 ## Where Vin (3) is the commercial input voltage, L26 is the inductance of the inductor 26,
t is the time from when the switch element 34 is turned on, and is set so that the current of the inductor 26 becomes zero amperes immediately before the switch element 34 is turned on. Therefore,
When the switching power supply of the circuit of the present invention is performing a steady operation, the ON width ton of the switch element 34 is considered to be substantially constant in a commercial AC cycle.
If the peak value of the current of the inductor 26 during one cycle of turning on and off at a high frequency is IL (peak1),

(Equation 6) Becomes Therefore, Vin (3) is a sine wave, and it can be seen from the above equation that the line connecting the peak value IL (peak) of the current of the inductor 26 is also a sine wave. Next, when the switch element 34 is turned off, the inductor 26

(Equation 7) Becomes Here, Vin (3) is the commercial input voltage, Vb is the voltage of the smoothing capacitor 32, and N3 is the tertiary winding 30 of the transformer 27.
Is the number of turns of the four control lines 31 of the transformer 27. Therefore, a time toff-1 from the time when the switch element 34 is turned off to the time when the current of the inductor 26 becomes zero amperes.
Is represented by the following equation.

(Equation 8) (8) Therefore, the sum of ton and toff-1 is

(Equation 9) The current waveform at this time is as shown in FIG. Therefore,
If the current of the inductor 26 is set so as to be always reset to zero amperes in the cycle of high-frequency switching, the inductor 2
The average value IL (ave) of the current 6 is expressed by the following equation, where to is the period of high-frequency switching.

(Equation 10) Here, Vin (3) is a commercial input voltage and is a sine wave.
When Vb is set to be 1.5 to 2 times or more larger than Vin (3), IL (ave) in the commercial cycle becomes approximately a sine wave. That is, for the current of the inductor 26 increasing and decreasing at a high frequency, immediately before the full-wave rectifier 21 or
Immediately thereafter, by using a low-pass filter for removing high-frequency ripple, the commercial input current waveform can be made approximately a sine wave, and the power factor can be increased.

In the above embodiment, the power factor is improved only by adding the control winding of the inductor 26 and the transformer 27 to the conventional AC input switching power supply. Further, the voltage applied to the inductor 26 while the switch element is off is a conventional AC input switching voltage.
In contrast to the difference voltage between the smoothing capacitor and the input voltage,
In the embodiment, since the input voltage is subtracted from the sum of the voltage of the smoothing capacitor and the voltage generated in the control winding of the transformer, the voltage of the smoothing capacitor required to reset the current of the inductor 26 is equal to that of the embodiment. In this case, the voltage generated in the control winding of the transformer can be made lower than that of the conventional AC input switching power supply. That is, a switch element having a low withstand voltage and a small on-resistance can be used as the switch element, and the efficiency of the switching power supply can be increased.

(9) FIG. 2 shows another embodiment of the present invention. In the figure, the same components as those of FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. 1 is different from the configuration of FIG.
Is connected between the terminals of the smoothing capacitor 32 via a diode 33, whereas the tertiary winding 30 of the transformer 27 is connected via a diode 33 in FIG. That is, it is connected between the terminals of the rectifying / smoothing capacitor 35.

2 differs from FIG. 2 in that when the switch element 34 is turned off, the inductor 2 in FIG.
6 flows into the smoothing capacitor 32 via the control winding of the transformer 27 and simultaneously flows through the control winding of the transformer 27. As a result, a corresponding current flows from the tertiary winding 30 of the transformer 27 to the diode. 33, the energy stored in the inductor 26 flows into the capacitor 39 of the rectifying / smoothing circuit 35, that is, while the switch element 34 is turned off by such a current flow, the smoothing capacitor 32 It is sent to the capacitor 39 of the rectifying / smoothing circuit 35. Other operations are the same as those in FIG. 1, and the same effects are obtained.

FIG. 3 is a circuit diagram showing another embodiment of the present invention, in which the tertiary winding 30 and the diode 33 of the transformer 27 are omitted. The switching capacitor 34 is turned on while the switch element 34 is on. Energy is stored in the transformer 27, and when the switching element is off, the energy stored in the transformer 27 is sent to the load via the rectifying and smoothing circuit 45, and at the same time, the current of the inductor 26 is As a result of flowing into the smoothing capacitor 32 via the control winding 31 of the transformer 27 and simultaneously flowing through the control winding 31 of the transformer 27, a current corresponding thereto flows from the secondary winding 29 of the transformer 27 to the capacitor of the rectifying and smoothing circuit 45. It flows into 47. That is, while the switch element 34 is off, the energy stored in the inductor 26 is sent to the smoothing capacitor 32 and the capacitor 47 of the rectifying and smoothing circuit 45. Other operations are the same as those in FIG. 1, and the same effects are obtained. (10)

FIG. 4 is a circuit diagram of another embodiment of the present invention. In this embodiment, a capacitor 50 is connected between the terminals of the switch element 34 as compared with FIG. This operation is performed after the exciting current of the transformer 27 is reset to zero amperes while the switch element 34 is off, and before the switch element 34 is turned on before the exciting inductance of the transformer 27 and the capacitor 50 resonate. Since the voltage between terminals of the switching element 34 is reduced to near zero volt, the switching loss at the time of turning on the switching element can be reduced.

FIG. 5 shows another embodiment of the present invention, in which a capacitor 48 is connected in series with the control winding 31 of the transformer 27, and a diode 49 is connected in parallel with the series circuit. When the switch element 34 is ON, the current of the inductor 26 is
Flows through the control winding, the primary winding 28, and the switching element 34, the capacitor 48 starts to have a voltage. When the voltage becomes higher than the voltage of the smoothing capacitor 32, the current of the inductor 26 Through the capacitor 49 and into the smoothing capacitor 32. That is, although the switching element 34 is on, the inductor 26
The boosting time becomes shorter as the input voltage Vin (4) becomes higher. Also, while the switch element 34 is off, the current of the inductor 26 is
9, the exciting current from the control winding of the transformer 27 flows through the capacitor 48 and the diode 49, and the capacitor 48 is turned on when the switch element 34 is turned on. Is charged in the opposite direction and the voltage drops. That is, in this embodiment, the boosting time of the inductor 26 becomes shorter as the input voltage Vin (4) becomes higher.
Even in a continuous mode that does not return to zero amps during the period when 4 is off, the input current waveform Iin (4) becomes a waveform substantially corresponding to a sine wave, and the power factor increases.

(11) FIG. 6 is a circuit example of another embodiment of the present invention.
From the positive side of the smoothing capacitor 32, a series circuit of the first switch element 51, the primary winding 28 of the transformer 27, and the second switch element 52 is connected between the terminals of the smoothing capacitor. A connection point between the switch element 51 and the primary winding 28 of the transformer 27 and the smoothing capacitor 3
A first diode 54 is connected to the negative side of the second switching element 52 and a connection point between the primary winding 28 of the transformer 27 and the second switch element 52 and the positive side of the smoothing capacitor 32. The point is that the second diode 53 is connected. In this circuit example, the first switch element 51 and the second switch 52 are simultaneously turned on or off at the same time, so that the smoothing capacitor 3 is turned on while the two switches are on.
2 is applied to the primary winding of the transformer 27, and the energy of the smoothing capacitor 32 is sent from the primary winding 28 of the transformer 27 to the load 40 via the secondary winding 29 and the rectifying and smoothing circuit 35. . At the same time, the current of the inductor 26 flows from the quaternary winding 31 of the transformer 27 via the first switch element 51, the primary winding 28 of the transformer 27, and the second switch element 52. On the other hand, when the switch elements 51 and 52 are off, the excitation energy of the transformer
Is a path from both terminals of the primary winding 28 of the transformer 27 to the smoothing capacitor 32 via a first diode 54 and a second diode 53, respectively. Can be The current of the inductor 26 is
Smoothing capacitor 3 via control winding 31 of transformer 27
2 and at the same time, a current flows through the control winding 31 of the
7 through the first diode 54 and the second diode 53 to the smoothing capacitor 32.

[0019]

As described above, according to the present invention, the switching element 34 is different from the conventional AC input switching power supply.
In addition, the control circuit 41 can easily increase the power factor as it is in the related art, and can set the voltage of the smoothing capacitor 32 low compared to the second configuration of the conventional AC input switching power supply. Therefore, a switching element having a low withstand voltage and a small on-resistance can be used, and the efficiency of the switching power supply can be improved.

[Brief description of the drawings]

 1 is a circuit diagram of one embodiment of the present invention. FIG. 2 is a circuit diagram of another embodiment of the present invention. FIG. 3 is a circuit diagram of another embodiment of the present invention. FIG. 4 is a circuit diagram of another embodiment of the present invention. FIG. 6 is a circuit diagram of another embodiment of the present invention. FIG. 7 is an operation waveform diagram of each part of the embodiment of the present invention (FIG. 1). FIG. 8 is a conventional circuit diagram. FIG. 9 is a conventional circuit diagram. Operation waveform diagram Figure 11 Operation waveform diagram of each part of conventional circuit (Figure 9)

[Explanation of symbols]

 2, 21 Full-wave rectifier 16, 26, 38 Inductor 8, 27 Transformer 28 Primary winding 29 Secondary winding 30 Tertiary winding 31 Control winding 32 Smoothing capacitor 11, 17, 34 Switch element 35 Rectifying smoothing circuit 40 load

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H02M 7/00-7/40 H02M 3/00-3/44

Claims (6)

(57) [Claims] 1. A smoothing capacitor is connected between output terminals of a full-wave rectifier connected to an AC power supply, and a series circuit of a primary winding of a transformer and a switch element is connected between terminals of the smoothing capacitor. A rectifying / smoothing circuit is connected to the secondary winding to supply power to a load connected between the output terminals of the rectifying / smoothing circuit, and at the same time, detect an output voltage of the rectifying / smoothing circuit to obtain a predetermined voltage. As described above, in a switching power supply including a control circuit for controlling the switching element, a switching power supply characterized by connecting an inductor and a control winding of the transformer in series between the full-wave rectifier and the smoothing capacitor. . 2. The switching power supply according to claim 1, wherein a capacitor is connected between the terminals of the switching element. 3. The switching power supply according to claim 1, wherein a capacitor is provided in series with the control winding, and a diode is connected in parallel with a series circuit of the control winding and the capacitor. 4. A smoothing capacitor is connected between output terminals of a full-wave rectifier connected to an AC power supply, and a first switch element, a primary winding of a transformer, and a second switch element are connected between the terminals of the smoothing capacitor. Connected in series, and
A rectifying / smoothing circuit is connected to the next winding, and power is supplied to a load connected between output terminals of the rectifying / smoothing circuit, and at the same time, an output voltage of the rectifying / smoothing circuit is detected so that the voltage becomes a predetermined voltage. A switching power supply having a control circuit for controlling the switch element, wherein an inductor and a control winding of the transformer are connected in series between the full-wave rectifier and the smoothing capacitor; Between the connection point of the primary winding and the negative side of the smoothing capacitor, a first
A switching power supply, wherein a second diode is connected between a connection point between the primary winding and the second switch element and a positive side of the smoothing capacitor. 5. A smoothing capacitor is connected between output terminals of a full-wave rectifier connected to an AC power supply, and a series circuit of a primary winding of a transformer and a switching element is connected between terminals of the smoothing capacitor. A rectifying / smoothing circuit is connected to the secondary winding to supply power to a load connected between the output terminals of the rectifying / smoothing circuit, and at the same time, detect an output voltage of the rectifying / smoothing circuit to obtain a predetermined voltage. As described above, in a switching power supply provided with a control circuit for controlling the switching element, the secondary winding of the transformer is connected between the terminals of the smoothing capacitor via a diode, and the full-wave rectifier and the smoothing capacitor are connected. A switching power supply, wherein an inductor and a control winding of the transformer are connected in series between capacitors. 6. A smoothing capacitor is connected between output terminals of a full-wave rectifier connected to an AC power supply, and a series circuit of a primary winding of a transformer and a switching element is connected between terminals of the smoothing capacitor. A rectifying / smoothing circuit is connected to the secondary winding to supply power to a load connected between the output terminals of the rectifying / smoothing circuit, and at the same time, detect an output voltage of the rectifying / smoothing circuit to obtain a predetermined voltage. As described above, in a switching power supply provided with a control circuit for controlling the switch element, a tertiary winding of a transformer and a series circuit of a diode are connected between output terminals of a rectifying and smoothing circuit, and the full-wave rectifier and the smoothing circuit are connected to each other. A switching power supply, wherein an inductor and a control winding of the transformer are connected in series between capacitors.