JP3402031B2 - DC power supply - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC power supply for supplying power from an AC power supply to a DC load. [0002] In recent years, harmonic currents generated in power supplies have become a problem. As a countermeasure, there are roughly two types: a method using an active element to make the input current close to a sine wave; and a method using a passive element to shape the input current waveform to increase the power factor. Among them, the former can suppress the higher harmonics more. However, it requires two converters, is costly, and has many disadvantages such as a large size, and it is advantageous to use a passive element of the latter type except for a power supply having a large output. Conventionally, techniques for dealing with harmonics using passive elements include a choke input method which has been used for a long time, and a partial smoothing method represented by, for example, Japanese Patent Application Laid-Open No. 54-158644. . FIG. 8 is a circuit diagram showing an example of a conventional choke input type power supply circuit. In the figure, 1 is an AC power supply, 2 is a rectifier circuit, 3 is a load, 7, 8 are output terminals, 21
Is a capacitor, and 22 is a choke coil. Here, the one without the choke coil 22 is a so-called capacitor input type power supply. The AC power supply 1 is connected to the input terminal of the rectifier circuit 2, and the capacitor 2 is connected to both ends of the output terminals 7 and 8.
1 and a load 3 are connected. This capacitor 21
The smoothed full-wave rectified voltage output from the rectifier circuit 2 is supplied to the load 3. In the choke input method, a choke coil 22 is inserted before the capacitor 21 of the output terminal 7 on the positive electrode side. With this choke coil 22, the power factor can be improved by blunting the input current waveform. However, in this choke input method, the power factor is about 70%, and for example, a high power factor of about 85% cannot be expected. In addition, since a large input current flows through the choke coil 22 when charging the capacitor 21, there is a disadvantage that the choke coil 22 becomes very large and heavy. On the other hand, in the partial smoothing method, the voltage at both ends of the smoothing capacitor is made lower than that of the conventional capacitor input type power supply, so that the period in which the full-wave rectified voltage is higher than the voltage at both ends of the smoothing capacitor. By increasing the length, the conduction angle of the input current is widened and the power factor is improved. FIG. 9 is a circuit diagram showing an example of a power supply circuit of a conventional partial smoothing system. In the figure, the same parts as those in FIG. 8 are denoted by the same reference numerals. 5 and 6 are capacitors, 9 to 11
Is a diode. The example shown in FIG.
This is a circuit described in FIG. 7 in 158644. A capacitor 5 is connected to the output terminals 7 and 8 of the rectifier circuit 2.
And 6 are connected in series with the diode 9 interposed therebetween, and the diode 10 is connected to the diode 9 and the capacitor 6.
And the diode 11 is connected in parallel with the capacitor 5
And the diode 9 are connected in parallel. In this circuit, at the time of charging, two smoothing capacitors 5 and 6 are charged in a series relationship via a diode 9. During discharging, the capacitor 5 and the diode 10 and the diode 11 and the capacitor 6 are discharged in a parallel relationship. At this time, the voltage between both ends of the capacitors 5 and 6 is half that of the conventional capacitor input type power supply. for that reason,
The input current flows until the full-wave rectified voltage output from the rectifier circuit 2 becomes １ ／, and the conduction angle can be increased. FIG. 10 is a circuit diagram showing another example of a conventional power supply circuit of the partial smoothing system. In the figure, the same parts as those in FIGS. 8 and 9 are denoted by the same reference numerals. 31 is a transformer, 32
Is a second rectifier circuit, and 33 is a diode. The circuit shown in FIG. 10 is a similar circuit of the partial smoothing method.
FIG. 6 of JP-A-9-81899. In this circuit, a diode 33 and a capacitor 21 are connected to both ends of output terminals 7 and 8 of the rectifier circuit 2. Further, the voltage is dropped by the transformer 31, full-wave rectified by the second claim circuit 32, and applied to both ends of the capacitor 21. According to such a circuit, charging of the capacitor 21 is performed by the full-wave rectified voltage stepped down by the transformer 31 and rectified by the rectifier circuit 32, and discharging is performed by the full-wave rectified voltage of the rectifier circuit 2. This is done via the diode 33 after the voltage has dropped. Therefore, since the input current flows until the full-wave rectified voltage output from the rectifier circuit 2 falls below the peak voltage of the rectifier circuit 32, the conduction angle of the input current can be widened. In this circuit, the potential of the capacitor 21 can be arbitrarily set by the transformer 31. In such a conventional partial smoothing method, the conduction angle can be wider than in the choke input method.
However, even in this partial smoothing method, when the capacitors 5 and 6 are charged, a current waveform similar to that of the capacitor input type power supply is observed. Therefore, the charging current of the capacitor contains many harmonic components, and the power factor does not improve as expected. In addition, these partial smoothing type power supply circuits use, for example, IEC1000-3-2 which is an international standard and EN1 which is a European standard, due to the harmonic components.
There is also a problem that harmonic regulation such as 000-3-2 cannot be handled. SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has been made to improve the power factor by reducing harmonic components of the charging current of a smoothing capacitor. It is an object of the present invention to provide a DC power supply that can cope with harmonic regulations in international standards and European standards. [0010] The present invention provides a rectifier circuit for rectifying an AC input voltage input from an AC power supply and outputting a rectified voltage, and smoothing the rectified voltage of the rectifier circuit to a load. In a DC power supply device having a smoothing circuit for outputting, the smoothing circuit includes a first smoothing capacitor, a charging circuit, and a second smoothing capacitor.
A smoothing capacitor connected in series in this order between the output terminals of the rectifier circuit, and connected in parallel to the charging circuit and the second smoothing capacitor to discharge the first smoothing capacitor. A first discharging diode, a second discharging diode connected in parallel to the first smoothing capacitor and the charging circuit for discharging the second smoothing capacitor, the charging circuit comprising: A charging diode for charging the first smoothing capacitor and the second smoothing capacitor in series with a rectified voltage from the rectifier circuit, and an impedance circuit for suppressing a maximum value of a charging current. A load current detection circuit for detecting a load current flowing through the circuit, and the impedance circuit is detected by the additional current detection circuit. In accordance with the load current, when the load current is large, the impedance is reduced to improve the conversion efficiency in the power supply, and when the load current is small, the impedance is increased and the power factor is controlled to improve the power factor. It is characterized by the following. FIG. 1 is a circuit configuration diagram for explaining a basic configuration of a DC power supply device according to the present invention. In the figure,
1 is an AC power supply, 2 is a rectifier circuit, 3 is a load, 4 is a smoothing circuit, 5 and 6 are capacitors, 7, 8 are output terminals, 9 to 11
Is a diode, 12 is a charging circuit, and 13 is a resistor.
The rectifier circuit 2 performs full-wave rectification on the AC input voltage input from the AC power supply 1 and outputs a full-wave rectified voltage _VIN . The smoothing circuit 4 smoothes the full-wave rectified voltage V _IN output from the rectifier circuit 2 and outputs an output voltage _VDC to the load 3. The smoothing circuit 4 includes smoothing capacitors 5 and 6
, A charging circuit 12 and diodes 10 and 11. The capacitor 5, the charging circuit 12, and the capacitor 6 are connected in series in this order, and are connected to the output terminals 7, 8 of the rectifier circuit 2. The diode 10 is connected in parallel with the charging circuit 12 and the capacitor 6, and conducts when the capacitor 5 is discharged. Also, the diode 11
Is connected in parallel with the capacitor 5 and the charging circuit 12, and becomes conductive when the capacitor 6 discharges. The charging circuit 12 includes a diode 9 and a resistor 13 connected in series as an impedance circuit. Diode 9 conducts when capacitors 5 and 6 are charged. Note that the resistor 13 may be arranged on either side of the diode 9. Since the resistor 13 acts to suppress the current during charging, it also has the effect of suppressing the inrush current when AC is applied. This eliminates the need for a rush current limiting circuit using a triac, which is generally found in a capacitor input type power supply, and also eliminates the so-called secondary rush current when the triac is conducting. Next, an example of the operation of the DC power supply device described with reference to FIG. 1 will be described. FIG. 2 is an explanatory diagram of a charging current, and FIG.
Is an explanatory diagram of a discharge current, and FIG. 4 is a waveform diagram of a voltage and an input current of each unit. In FIG. 4, (a) is the voltage waveform of the full-wave rectified voltage V _IN , (b) is the voltage waveform between the terminals of the capacitors 5 and 6, (c) is the waveform of the sum of the voltages between the terminals of the capacitors 5 and 6, ( d) is the voltage waveform of the output voltage VD _CV , (e)
Indicates the input current waveform. A indicates the discharging period of the capacitors 5 and 6, B indicates the period during which the smoothing circuit 4 does not function, and C indicates the charging period of the capacitors 5 and 6. First, at the time of charging the capacitors 5 and 6, the charging is performed by a series circuit of the capacitor 5, the resistor 13, the diode 9, and the capacitor 6, as indicated by an arrow in FIG. Therefore, each of the capacitors 5 and 6 is charged with half the voltage of the capacitor in the case of a conventional capacitor input type power supply. FIG. 4B shows the voltage between the terminals of the capacitors 5 and 6. FIG. 4C indicated by a broken line shows the sum of the voltages between the terminals of the capacitors 5 and 6.
It corresponds to the voltage charged to the smoothing capacitor by the conventional capacitor input type power supply. Since the capacitors 5 and 6 are in a serial relationship at the time of charging, the charging is performed while the full-wave rectified voltage V _IN exceeds the sum of the voltages between the terminals of the capacitors 5 and 6. This period is shown as period C in FIG. As the battery is charged, the voltage between the terminals of the capacitors 5 and 6 rises.
Is the full-wave rectified voltage V _IN . The output voltage _VDC during this period C is also the full-wave rectified voltage V _IN . In this period C, capacitors 5 and 6
, A large input current flows, and the waveform becomes as shown in a period C in FIG. However, since the maximum value of the charging current is suppressed by the resistor 13, a steep large current does not flow as in the related art, and generation of a high frequency can be suppressed. The peak value of the charging current can be controlled by the constant of the resistor 13. Now, after a lapse of time, when the full-wave rectified voltage V _IN becomes lower than the sum of the voltages between the terminals of the capacitors 5 and 6,
Naturally, the capacitors 5 and 6 are not charged. At this time, in the conventional capacitor input type power supply, energy is supplied from the capacitor to the load 3, but in the present invention, a series circuit of the capacitor 5 and the diode 10 and a series circuit of the diode 11 and the capacitor 6 as shown in FIG. Are discharged in a circuit connected in parallel. Therefore, during a period in which the full-wave rectified voltage V _IN is higher than the voltage between the terminals of the capacitors 5 and 6 shown in FIG. 4B, energy is supplied to the load 3 by the input current. This period is period B shown in FIG. The output voltage _VDC in this section B is the full-wave rectified voltage V _IN . Also, the waveform of the input current differs depending on the state of the load.
_Since the product with _DC becomes constant, the waveform becomes as shown in FIG. Further, when the full-wave rectified voltage V _IN decreases and becomes lower than the voltage between the terminals of the capacitors 5 and 6, the capacitors 5 and 6 start discharging and supply energy to the load 3. As described above, capacitors 5 and 6 as shown in FIG.
Discharge is performed by the parallel relationship of. At this time, since the discharge is performed without passing through the resistor 13, the loss at the time of the discharge is small. The period during which the capacitors 5 and 6 discharge is the period A shown in FIG. The output voltage V _DC during this period A
Is the voltage between the terminals of the capacitors 5 and 6. Also, the input current in this period A is 0 A naturally. The discharge of the capacitors 5 and 6 is performed when the full-wave rectified voltage V _IN
6 until the voltage exceeds the inter-terminal voltage. As described above, the waveform of the output voltage _VDC is, as shown in FIG. 4D, the full-wave rectified voltage V _IN shown in FIG. 4A and the capacitor shown in FIG. The trace of the higher voltage between the terminals 5 and 6 is obtained. When the load 3 is a constant power load, the input current waveform is the input current waveform shown in FIG. In the conventional capacitor input type power supply, the input power supply is in a period C in FIG.
Therefore, the conduction angle of the input current is widened, and the peak of the input current in the period C is also suppressed by the resistor 13, so that the high-frequency component is reduced and the power factor is significantly improved. Understand. FIG. 5 is a graph showing the load characteristics of the power factor when the constant of the resistor 13 is changed in the DC power supply device described with reference to FIG. The DC power supply used for the measurement of the graph shown in FIG.
It is. In FIG. 5, ○ indicates a graph when the resistance 13 is 0Ω, □ indicates a resistance of 22Ω, and Δ indicates a resistance of 33
The graph at the time of Ω is shown. As can be seen from FIG. 5, the power factor of the DC power supply device in which the resistor 13 is inserted is much better than that of a conventional power supply circuit in which the resistor 13 is 0Ω, that is, the conventional power supply circuit without the resistor 13. The resistor 1 shown in FIG.
3 is 22Ω and 33Ω, the output current is 1 to 1.5A
Thus, a power factor of 85% or more is obtained. FIG. 6 is a circuit diagram showing a first embodiment of the DC power supply according to the present invention. In the figure, the same parts as those in FIG. 14 is a choke coil. In the first embodiment, the choke coil 14 is inserted in the charging circuit 12 in series. With the choke coil 14, the capacitors 5,
At the time of charging of the capacitor 6, that is, during the period C in FIG. 2, the charging current waveforms of the capacitors 5 and 6 are smoothed to increase the conduction angle of the charging current. Unlike the conventional choke input type power supply, not all the input current flows through the inductance element, but only the charging current of the capacitors 5 and 6, so the winding diameter is smaller than that of the choke used in the conventional choke input method. It is possible to reduce the size of the choke and expect high reactance with the same shape. The order of arrangement of the diode 9, the resistor 13, and the choke coil 14 in the charging circuit 12 is arbitrary. FIG. 7 is a circuit diagram showing a second embodiment of the DC power supply according to the present invention. In the figure, the same parts as those in FIG. Reference numeral 15 denotes a variable impedance circuit, and reference numeral 16 denotes a load current detection circuit.
In the DC power supply device described with reference to FIG. 1, as shown in FIG. 5, it can be seen that the power factor increases as the load increases and the output current increases. On the other hand, the conversion efficiency of the DC power supply device decreases because the power consumption of the resistor 13 during charging of the capacitors 5 and 6 increases as the load increases. Therefore, the second embodiment shows an example in which the variable impedance circuit 15 is provided in the charging circuit 12 in order to balance the power factor and the efficiency.
The variable impedance circuit 15 changes the impedance based on the detection result of the load current by the load current detection circuit 16. For example, when the load current is large, the impedance can be reduced to improve the conversion efficiency of the power supply, and when the load current is small, the impedance can be increased to improve the power factor. The method of detecting the load current in the load current detection circuit 16 is not limited. For example, the load current can be easily detected from the voltage across the current detection resistor of the switching FET. Of course, the control of the impedance of the variable impedance circuit 15 can be fine or coarse depending on the requirements of the load 3. According to the present invention, in addition to the resistors, choke coils, variable impedance circuits, or combinations thereof described in the above-described embodiments, any impedance element is applied to the impedance circuit in the charging circuit 12. Is also good. For example, in some cases, the impedance can be controlled without detecting the load current by using a thermistor or the like, if required by the load side. In each of the above embodiments, a bridge type full-wave rectifier circuit is shown as a rectifier circuit. However, the present invention is not limited to this. And various rectifier circuits. As is apparent from the above description, according to the present invention, by providing the impedance circuit which operates only when charging the smoothing capacitor, the peak of the input current during charging is suppressed, By reducing the current, it is possible to configure a DC power supply device capable of complying with, for example, harmonic regulation according to the international standard IEC1000-3-2 or the European standard EN1000-3-2. In addition, since the inrush current at the time of AC input is suppressed by the impedance in the charging circuit, the inrush current suppression circuit and the like provided in the previous stage of the conventional rectifier circuit can be omitted, and the cost can be reduced. A DC power supply can be realized. Furthermore, by performing the discharging of the smoothing capacitor in parallel, there are various effects such as the conduction angle of the input current can be widened. As the impedance circuit, in addition to the resistor,
An inductance element as described in the second aspect can be used. With this inductance element, 2
The conduction angle of the charging current of the individual smoothing capacitors can be widened, and the harmonic current can be further reduced. Here, since only the charging current of the two smoothing capacitors flows through this inductance element, it may be smaller than the choke used in the conventional choke input method, or high reactance can be expected with the same shape. According to the DC power supply device of the third aspect,
By providing a circuit for detecting the state of the load and changing the impedance of the impedance circuit according to the load, there is an effect that a DC power supply device having both a power factor and a conversion efficiency can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit configuration diagram for explaining a basic configuration of a DC power supply device of the present invention. FIG. 2 is an explanatory diagram of a charging current in the DC power supply device of FIG. FIG. 3 is an explanatory diagram of a discharge current in the DC power supply device of FIG. FIG. 4 is a waveform diagram of voltages and input currents of respective units in the DC power supply device of FIG. FIG. 5 is a graph showing load characteristics of a power factor when the constant of the resistor 13 is changed in the DC power supply device of FIG. FIG. 6 is a circuit configuration diagram showing a first embodiment of the DC power supply device of the present invention. FIG. 7 is a circuit configuration diagram showing a second embodiment of the DC power supply device of the present invention. FIG. 8 is a circuit diagram illustrating an example of a conventional choke input type power supply circuit. FIG. 9 is a circuit diagram showing an example of a conventional power supply circuit of a partial smoothing system. FIG. 10 is a circuit diagram showing another example of a power supply circuit of a conventional partial smoothing system. [Description of Signs] 1 ... AC power supply, 2 ... Rectifier circuit, 3 ... Load, 4 ... Smoothing circuit, 5,6 ... Capacitor, 7,8 ... Output terminal, 9-11
... Diode, 12 ... Charging circuit, 13 ... Resistance, 14 ...
Choke coil, 15 ... variable impedance circuit, 16
... Load current detection circuit.

Claims (1)

(57) [Claim 1] A rectifier circuit for rectifying an AC input voltage input from an AC power supply and outputting a rectified voltage, and smoothing the rectified voltage of the rectifier circuit and outputting the rectified voltage to a load. In a DC power supply device provided with a smoothing circuit, the smoothing circuit connects a circuit in which a first smoothing capacitor, a charging circuit, and a second smoothing capacitor are connected in series in this order, between output terminals of the rectifier circuit, A first discharging diode connected in parallel to the charging circuit and the second smoothing capacitor for discharging the first smoothing capacitor, and connected in parallel to the first smoothing capacitor and the charging circuit; The second
A second discharging diode for discharging the smoothing capacitor, and the charging circuit charges the first smoothing capacitor and the second smoothing capacitor in series with a rectified voltage from the rectifier circuit. A charging diode, and an impedance circuit that suppresses the maximum value of the charging current, and a load current detection circuit that detects a load current flowing through the load is provided, and the impedance circuit is an additional current detection circuit. According to the detected load current, when the load current is large, the impedance is reduced to improve the conversion efficiency in the power supply, and when the load current is small, the impedance is increased and the power factor is controlled to improve the power factor. A DC power supply device, characterized in that: