JP3127979B2 - DC 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 DC power supply capable of improving a power factor.

[0002]

2. Description of the Related Art When a DC power supply of a switching power supply is constructed by connecting a rectifying and smoothing circuit to a commercial AC power supply, a charging current flows through a smoothing capacitor only in a peak region of a sine wave AC voltage, and an input current waveform and power The rate gets worse. In order to solve this kind of problem, a power factor improving circuit may be provided in a stage preceding the switching regulator circuit. However, if the power factor correction circuit and the switching regulator circuit are separately provided, the power supply device becomes large and expensive.

In order to solve this kind of problem, it is conceivable to share a switch with a power regulator and a switching regulator as shown in FIG. In the DC power supply device of FIG. 1, a commercial AC power supply is connected to AC power supply terminals 1 and 2 via a high frequency filter (not shown), and a bridge type rectifier circuit 3 including diodes D1, D2, D3 and D4. Is connected between the one output terminal and the other output terminal (ground), a reactor (inductance circuit element) 4, a diode 5, and a primary winding 7 of an output transformer 6.
And a series circuit of a switch 8 comprising a field effect transistor. A diode 9 is connected between the output terminal of the reactor 4 and an upper end of the switch 8, and a smoothing capacitor 10 is connected between a cathode of the diode 5 and a lower terminal of the rectifier circuit 3. Transformer 6-2
The secondary winding 11 is connected to an output rectifying / smoothing circuit including an output rectifying diode 12 and an output smoothing capacitor 13. Note that the diode 12 has a direction of turning on when the switch 8 is off. A pair of DC output terminals 14
a and 14b are connected to both ends of the capacitor 13.

The switch 8 is set to a repetition frequency (for example, 20 kHz) higher than the frequency of, for example, 50 Hz of the AC power supply terminals 1, 2.
The control circuit 15 for performing the on / off operation in z) includes resistors 16 and 17 as voltage detecting means connected between the output terminals 14a and 14b, and one of the input terminals is connected to the resistors 16 and 17
And the other input terminal is connected to the reference voltage source 18.
, A triangular wave generator 20 that generates a triangular wave at a switching cycle, one input terminal is connected to the output of the error amplifier 19, and the other input terminal is connected to the triangular wave generator 20, Voltage comparator 21 whose output terminal is connected to the control terminal (gate) of switch 8
Consisting of The error amplifier 19 outputs a voltage corresponding to the difference between the detection voltage and the reference voltage, and the comparator 21 compares the triangular wave with the error output to form a PWM pulse, and sends this to the switch 8.

In the circuit shown in FIG. 1, while the switch 8 is on, a current flows through a circuit including the reactor 4, the diode 9, and the switch 8, and energy is stored in the reactor 4. During the off period of the switch 8, the diode 5 is turned on by the output voltage of the rectifier circuit 3 and the voltage (accumulated energy) of the reactor 4, and the capacitor 10 is charged.
When the switch 8 is turned on while the capacitor 10 is charged, a current flows through the reactor 4 in a circuit of the reactor 4, the diode 9 and the switch 8, and the capacitor 10, the primary winding 7 and the switch 8 are closed as a DC power supply. Current also flows through the circuit. At this time, since a downward voltage is generated in the secondary winding 11, the output rectifying diode 12 is kept off, and magnetic energy is accumulated in the transformer 6.
After that, during the OFF period of the switch 8, the capacitor 10 is charged as described above and the transformer 6 is turned off.
, The output rectifying diode 12 is turned on, and a charging current flows through the capacitor 13. The capacitor 10 functioning as a DC power supply is charged to a voltage higher than the peak of the output voltage of the rectifier circuit 3 (about twice the power supply voltage) by the boosting action of the reactor 4.

When the output voltage of the circuit shown in FIG. 1 becomes lower than a desired value, the duty ratio of the PWM wave increases, and the ON time width of the switch 8 increases. Conversely, when the output voltage becomes higher than the desired value, the duty ratio of the PWM wave becomes smaller, and the ON time width of the switch 8 becomes shorter.

[0007]

Since the capacitor 10 is charged higher than the power supply voltage, an expensive and large capacitor with a high withstand voltage is required.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a DC power supply capable of reducing the size and cost and improving the power factor.

[0009]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a rectifier circuit connected to an AC power supply terminal, a reactor having one end connected to one output terminal of the rectifier circuit, and An intermittent switch having one end connected to the other end of the reactor and the other end connected to the other output terminal of the rectifier circuit; a primary winding of an output transformer connected to one end of the switch; A power supply capacitor connected in parallel to a series circuit of a secondary winding and the switch; a secondary winding of the transformer; a rectifying and smoothing circuit connected to the secondary winding; And a control circuit for turning on and off the switch at a repetition frequency higher than the frequency of the applied AC voltage. In addition, as described in claim 2, it can be connected to the tap (intermediate terminal) of the primary winding of the reactor. Further, a DC bias power supply can be connected in series with the reactor. Further, the DC bias power supply may be constituted by a capacitor and a diode for charging the capacitor using the voltage of the primary winding. Further, as described in claim 5, a diode for charging the bias power supply capacitor can be connected between the power supply side terminal or tap (intermediate terminal) of the reactor and one end or tap of the primary winding. Further, as described in claim 6, a diode and a capacitor switch for performing a resonance operation can be provided.

[0010]

According to the present invention, the power supply capacitor is not directly connected to the output stage of the reactor but is connected through the primary winding of the transformer. Therefore, the voltage of the sum of the output voltage of the rectifier circuit and the voltage of the reactor obtained during the off period of the switch is divided and applied to the primary winding and the capacitor. Therefore, the voltage of the power supply capacitor is lower than that of the conventional circuit of FIG. 1, and the power supply capacitor can be reduced in size and cost. Since the amplitude of the current flowing through the reactor changes in accordance with the amplitude of the AC power supply voltage, the waveform improving effect and the power factor improving effect can be obtained in the same manner as in the conventional circuit. When a DC bias power supply is provided, the charging voltage of the power supply capacitor can be increased, and a current can flow through the reactor even during a period in which the amplitude of the AC power supply voltage is low. As described in claims 4 and 5, the charging of the power supply capacitor is performed by 1
By using the voltage of the next winding, the charging circuit can be simplified. According to the sixth aspect, the effect of reducing switching loss due to resonance can be obtained.

[0011]

First Embodiment Next, a DC power supply according to a first embodiment of the present invention will be described with reference to FIGS. However, FIG.
In FIG. 5, the same reference numerals are given to substantially the same portions as those in FIG. 1, and the description thereof is omitted. The DC power supply of FIG. 2 omits diodes 5 and 9 from the circuit of FIG. 1 and connects the upper end of the capacitor 10 to the reactor (inductance) 4 without connecting the diode 5 to the primary winding 7 only. , Are formed in the same manner as in FIG. Therefore, in the circuit of FIG. 2, the capacitor 10 is connected to the reactor 4 via the primary winding 7.
It is connected to the.

[0012]

[Operation] As shown in FIG. 3A, the comparator 21 outputs a comparison output pulse between the triangular wave V1 supplied from the triangular wave generation circuit 20 and the voltage V2 supplied from the error amplifier 19 as shown in FIG. appear. When this pulse is supplied to the gate of the switch 8, the switch 8 performs an ON / OFF operation (intermittent operation) in response thereto, and a drain current Id flows as shown in FIG. 3C during the ON period.

During the ON period of the switch 8, a current flows through the circuit of the rectifier circuit 3, the reactor 4, and the switch 8. If the capacitor 10 is already charged, the capacitor 1
A current also flows in the closed circuit of 0, primary winding 7 and switch 8. When a current flows from the top to the bottom of the primary winding 7, a downward voltage is generated in the secondary winding 11, so that the diode 12 is kept off and energy is stored in the transformer 6. The current I1 flowing through the reactor 4 is shown in FIG.
3 (E), the peak value increases with a slope, and this peak value is equal to the output voltage Vin of the rectifier circuit 3 shown in FIG. 3 (D).
It changes according to the amplitude of. During the off period of the switch 8, the rectifier circuit 3, the reactor 4, the primary winding 7, and the capacitor 10
Current flows through the circuit. No charging current flows through the reactor 4 during a period when the charging voltage of the capacitor 10 is higher than the sum of the output voltage Vin of the rectifier circuit 3 and the voltage of the reactor 4. Since the sum of the output voltage Vin of the rectifier circuit 3 and the voltage of the reactor 4 during the off period of the switch 8 is applied to the series circuit of the primary winding 7 and the capacitor 10, a very high voltage is not applied to the capacitor 10. During the OFF period of the switch 8, the diode 12 is turned on, and a current based on the discharge of the stored energy of the transformer 6 and the charging current of the capacitor 10 flows through the diode 12 to the smoothing capacitor 13 and the load. The control for keeping the voltage between the output terminals 14a and 14b constant is the same as that of the circuit of FIG.

As is apparent from the above description, since the capacitor 10 is not charged to a high value, the miniaturization, the withstand voltage, and the cost can be achieved. Also, AC power supply terminals 1, 2
3E is connected to a high-frequency filter (not shown) to smooth the waveform shown in FIG. 3 (E), and has a waveform close to a sine wave with a good power factor.

[0015]

Second Embodiment Next, a DC power supply according to a second embodiment of the present invention will be described with reference to FIG. However, in FIG. 4, substantially the same parts as those in FIGS. 1 and 2 are denoted by the same reference numerals, and description thereof will be omitted. 4 is the same as FIG. 2 except that the output terminal of the reactor 4 is connected to the intermediate tap of the primary winding 7 of the transformer 6.

When the connection point of the reactor 4 is shifted to the tap of the primary winding 7 as shown in FIG. 4, a part of the primary winding 7 is connected between the reactor 4 and the switch 8, so that the switch 8 The current I1 flowing through the reactor 4 during the on-period becomes smaller. On the other hand, the charging voltage of the capacitor 10 increases. Therefore, the voltage of the capacitor 10 can be adjusted. Since the circuit of FIG. 4 has basically the same configuration as the circuit of FIG. 2, it has the same operation and effect.

[0017]

Third Embodiment Next, a DC power supply according to a third embodiment will be described with reference to FIG. However, in FIG. 5, substantially the same parts as those in FIGS. 1 and 2 are denoted by the same reference numerals, and description thereof will be omitted. The circuit of FIG. 5 is the same as that of FIG. 2 except that a bias power supply capacitor 22 and a diode 23 are added to the circuit of FIG. The bias power supply capacitor 22 is connected between the reactor 4 and one end of the primary winding 7, the diode 23 is connected between one end of the capacitor 22 and the tap of the primary winding 7,
2 has a direction of charging such that the right end is a positive electrode.
Since the capacitor 22 is charged with the downward voltage of the primary winding 7 and the capacitor 22 is connected in series to the reactor 4, the voltage of the rectifier circuit 3, the voltage of the reactor 4, and the voltage of the bias power supply capacitor 22 are output. Sum is primary winding 7
And the capacitor 10 in a series circuit.
Can be charged higher than in FIG. The period during which the sum voltage is higher than the voltage of the capacitor 10 is shown in FIG.
Therefore, the power factor improving effect is greater than that of the circuit of FIG. The basic circuit configuration of FIG.
Therefore, the circuit of FIG. 5 has the same operation and effect as FIG.

[0018]

Fourth Embodiment A DC power supply according to a fourth embodiment shown in FIG. 6 is obtained by shifting the positions of the capacitor 22 and the diode 23 shown in FIG. ing. That is, the condenser 22 is connected to the reactors 4 and 1
It is connected between the tap of the next winding 7. Since the circuit configuration of FIG. 6 is obtained by adding the capacitor 22 to the circuit of FIG. 4 as in FIG. 5, it has both the effect of the circuit of FIG. 4 and the effect of the capacitor 22 of FIG. Note that diode 2
As shown by the dotted line in FIG.
Can be moved to the top of

[0019]

Fifth Embodiment A DC power supply according to a fifth embodiment shown in FIG. 7 is different from the DC power supply shown in FIG.
It is configured identically. The diode 23 is connected between an intermediate tap of the reactor 4 and an upper end of the primary winding 7. Thereby, the bias capacitor 22 can be charged with the smoothing action of the reactor 4. Note that the anode of the diode 23 is moved to the left end of the reactor 4 as shown by a dotted line, the cathode of the diode 23 is connected to the tap of the primary winding 7,
Can be connected to the tap of the primary winding 7 as shown by the dotted line. Since the circuit of FIG. 7 is basically the same as the circuit of FIG. 5, it has the same operation and effect.

[0020]

Sixth Embodiment Next, a DC power supply according to a sixth embodiment will be described with reference to FIGS. However, in FIG. 8, substantially the same parts as those in FIG. 4 are denoted by the same reference numerals, and the description thereof will be omitted. The circuit of FIG. 8 is the same as that of FIG. 4 except that a resonance capacitor Cx and a resonance switch Qx formed of a field effect transistor are added to the circuit of FIG. A series circuit of the resonance capacitor Cx and the switch Qx is connected in parallel to the intermittent switch 8.
Since the two switches 8 and Qx are both insulated gate type field effect transistors whose sources are connected to a substrate (bulk), as shown in FIG.
S2 has diodes D1 and D2 in antiparallel, and further has stray capacitances C1 and C2 in parallel with main switches S1 and S2. However, the diodes D1, D2 and the capacitor C1
, C2 can be connected as individual components.

The control circuit 24 for controlling the resonance switch Qx is used to turn on the switch Qx during the off period of the control signal Vg1 shown in FIG. 10B obtained from the control circuit 15 of the intermittent switch 8. FIG. 10 shows the control signal Vg2.
This occurs as shown in FIG. Note that there is a pause period during which both the first and second control signals Vg1 and Vg2 are turned off.

FIG. 10 shows the state of each part in FIG. 8. (A) and (C) show the voltage between the terminals (drain-source voltage) V1 and Vq of the switch 8 and Qx.
(B) and (D) show the control signals Vg1 and Vg2 applied to the gate of the switch 8 and Qx, and (E) and (F) show the main signals S1 and S2 of the switch 8 and Qx shown in FIG. (G) shows the resonance capacitors Cx.
The voltage Vcx of FIG.

The circuit of FIG. 8 has the same effect as that of FIG. 4 and also has the effect of reducing switching loss due to the partial resonance operation.

In the circuit of FIG. 8, t1 to t2 of FIG.
During the ON period of the switch 8 shown in FIG.
While a current flows through the closed circuit of the next winding 7 and the switch 8,
A current flows through the closed circuit of the rectifier circuit 3, the reactor 4, and the switch 8. When the intermittent switch 8 is controlled to be turned off at time t2, a current flows through the stray capacitance C1 of the switch 8 shown in FIG. 9, and the current is gradually charged. Therefore, the voltage V1 of the intermittent switch 8 becomes t2 as shown in FIG.
It gradually increases in the period from t3 to t3. Thereby, zero volt switching at the time of turn-off is achieved, and switching loss is reduced. When the charging of the stray capacitance C1 is completed at time t3, the capacitor 10, the primary winding 7, and the capacitor C
x and the main switch S2 of the resonance switch Qx or the diode D2, a current flows, and the rectifier circuit 3, the reactor 4, a part of the primary winding 7, and the capacitor C
Current flows through a closed circuit consisting of x and the main switch S2 or diode D2. Next, the capacitor Cx enters the discharging mode, and the capacitor Cx, the primary winding 7 and the capacitor 10
And a main switch S2, a current flows in the opposite direction (upward), and a current also flows in a closed circuit including the rectifier circuit 3, the reactor 4, the primary winding 7, and the capacitor 10. Note that since the capacitor Cx has a relatively large capacitance, this voltage Vcx is maintained at a substantially constant DC voltage as shown in FIG. Dripping. When the switch Qx is turned off at time t4, the stray capacitance C1 of the intermittent switch 8 is reversely charged, and this voltage, that is, the voltage V1 of the intermittent switch 8, decreases as shown in FIG. Capacity C1
Flows through a closed circuit of the capacitor 10, the capacitor C1, and the primary winding 7. As a result, the electric charge of the capacitor C1 is returned to the capacitor 10 or the capacitor 13 on the secondary side. At time t5, the intermittent switch 8 is turned on. When the current I1 flows through the switch 8, the voltage of the switch 8 is almost zero volt, and the switching loss is reduced.

The circuit of the capacitor Cx and the switch Qx can be added to the circuits of FIGS. 2, 5, 6, and 7. Thus, the same operation and effect as those in FIG. 8 can be obtained.

[0026]

[Modifications] The present invention is not limited to the above-described embodiment, and for example, the following modifications are possible. (1) The switch 8 can be a semiconductor switch such as a bipolar transistor. (2) The polarities of the rectifier circuit 3 and the switch 8 can be reversed. (3) The bias capacitor 22 can be used as a battery power source. Also, a tertiary winding for charging the capacitor 22 is provided in the transformer 6, and this voltage can be rectified by a diode and applied to the capacitor 22. The voltage of the capacitor 22 can be variably controlled. (4) In each embodiment, as shown in FIG. 11, the polarity of the windings 7 and 11 of the transformer 6 can be set to the forward type, and the diode 12 can be turned on during the ON period of the switch 8. . In this case, a smoothing reactor L0 and a diode D0 are added. (5) In each embodiment, as shown in FIG. 12, the secondary winding 11 of the transformer 6 can be a center tap type and can be rectified by the two diodes 12a and 12b. In this case, the diode 12a is turned on during the on period of the switch 8, and the diode 12b is turned on during the off period. (6) In each embodiment, as shown in FIG.
In this circuit, a diode D0 and a reactor L0 can be added. This improves the smoothness when the switch 8 is turned on. (7) In each embodiment, as shown in FIG.
A smoothing reactor L0 can be added to this circuit.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a conventional DC power supply device.

FIG. 2 is a circuit diagram illustrating a DC power supply device according to a first embodiment.

FIG. 3 is a waveform chart showing a state of each unit in FIG. 2;

FIG. 4 is a circuit diagram showing a DC power supply device according to a second embodiment.

FIG. 5 is a circuit diagram showing a DC power supply device according to a third embodiment.

FIG. 6 is a circuit diagram illustrating a DC power supply device according to a fourth embodiment.

FIG. 7 is a circuit diagram showing a DC power supply device according to a fifth embodiment.

FIG. 8 is a circuit diagram showing a DC power supply device according to a sixth embodiment.

9 is an equivalent circuit diagram of a part of FIG.

FIG. 10 is a waveform chart of each part in FIG. 8;

FIG. 11 is a diagram illustrating a transformer secondary-side circuit according to a modified example.

FIG. 12 is a diagram showing a transformer secondary circuit according to another modification.

FIG. 13 is a diagram showing a transformer secondary-side circuit of still another modification.

FIG. 14 is a diagram showing a transformer secondary-side circuit of still another modification.

[Explanation of symbols]

 4 Reactor 6 Transformer 8 Switch 10 Capacitor

Claims (6)

(57) [Claims] A rectifier circuit connected to an AC power supply terminal; a reactor having one end connected to one output terminal of the rectifier circuit; one end connected to the other end of the reactor; An intermittent switch connected to the other output terminal of the rectifier circuit; a primary winding of an output transformer connected to one end of the switch; and a parallel connection to a series circuit of the primary winding and the switch. A power supply capacitor, a secondary winding of the transformer, a rectifying / smoothing circuit connected to the secondary winding, and the switch at a repetition frequency higher than a frequency of an AC voltage applied to the AC power supply terminal. DC power supply device having a control circuit for controlling ON / OFF of the power supply. 2. The DC power supply according to claim 1, wherein the other end of the reactor is connected to a tap of the primary winding instead of being connected to one end of the switch. 3. The DC power supply device according to claim 1, wherein a DC bias power supply is connected in series with the reactor. 4. The DC power supply according to claim 3, wherein said DC bias power supply comprises a bias capacitor serving as a bias power supply, and a diode for charging said bias capacitor by a voltage of said primary winding. apparatus. 5. The DC bias power supply comprises: a bias capacitor connected between the other end of the reactor and one end of the switch or a tap of the primary winding; and one end or tap of the reactor and the first capacitor. 4. The DC power supply device according to claim 3, further comprising a diode connected between a terminal or a tap of the next winding on the power supply capacitor side. 6. A stray capacitance connected in parallel to the on / off switch or an individual capacitor connected in parallel to the on / off switch, and a built-in or individual capacitor connected in antiparallel to the on / off switch. A first resonance diode; a resonance switch connected in parallel to the intermittent switch via a capacitor; and a resonance switch having a direction opposite to that of the first resonance diode. A built-in or individual second resonance diode connected in parallel to the intermittent switch, from a point slightly after the start of the off-period of the intermittent switch to a point slightly before the end of the off-period of the intermittent switch. A DC power supply according to any one of claims 1 to 5, further comprising a control circuit for turning on the resonance switch.